Cycle 8 Abstract Catalog (based on Phase I Submissions) Generated on: Thu Dec 17 12:25:22 EST 1998 ================================================================================ Proposal Category: GO Scientific Category: FIELD STELLAR POPULATIONS ID: 8095 Title: Accurate proper motions of Galactic halo populations PI: Rodrigo Ibata PI Institution: European Southern Observatory We propose to use the superb spatial resolution of the WFPC2 camera to obtain second epoch exposures in the fields of several Galactic halo globular clusters and dwarf satellite galaxies. The proper motions of these populations will thereby be determined to unprecedented accuracy, approximately an order of magnitude better than has been previously possible. This will improve our understanding of the shape and distribution of the dark matter halo of the Milky Way, it will allow better scrutiny of formation models of the halo, it will allow us to investigate the dynamical evolution of the Galactic satellites, and it will help constrain the dynamics of foreground Galactic components. Stellar populations studies of the Galactic halo objects can be (in some cases, substantially) improved, since contaminants from foreground stellar populations and background galaxian populations will be excluded from color-magnitude diagrams and luminosity functions. Furthermore, we may also discover high redshift supernovae. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8096 Title: The interstellar medium near to and beyond the Galactic Center PI: Francis Keenan PI Institution: Queen's University of Belfast We have recently identified a B-type supergiant, LS 4825, which lies on the far side of the Galaxy, at a Galactocentric distance of R_G = 12 kpc, and whose sightline passes within 1 kpc of the Galactic Center. Optical ionCa2 and ionNa1 interstellar observations of LS 4825 reveal a miriad of intermediate and high velocity clouds, several of which arise from gas near to and beyond the Galactic Center. We now propose to obtain medium resolution STIS spectra, primarily to observe the ultraviolet interstellar lines towards LS 4825. These data will allow us to determine the abundances of important elements such as Mg, Si, S, Cr, Mn, Fe, and Zn (and possibly C, N, and O) in interstellar gas as a function of Galactocentric distance, from the Solar position all the way in to the Galactic Center and beyond, which is vital for testing the competing models for the chemical evolution of our Galaxy. A secondary aim of the STIS observations will be to study the ultraviolet stellar absorption lines in LS 4825, which will provide reliable element abundances for this star, and hence the chemical composition of the interstellar medium at R_G = 12 kpc on the far side of the Galaxy. This will be compared with results at R_G = 12 kpc on the near side, to investigate the azimuthal dependence of the Galactic abundance gradient. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8097 Title: C IV High Velocity Clouds: Remnants of the Local Group? PI: Kenneth Sembach PI Institution: The Johns Hopkins University We have recently studied two high velocity (V_LSR<-100 km s^-1) clouds (HVCs) in the direction of Mrk 509 that have unusual ionization properties. The clouds exhibit strong C IV absorption with little or no detectable low ion (C II, Si II) absorption or H I 21cm emission. Our Cycle 6 program to study the properties of the HVCs toward Mrk 509 in detail revealed that they are likely very low density, low pressure gas clouds in the Local Group (or distant Galactic halo) subject to the extragalactic ionizing background. Their ionization properties resemble those of the outer diffuse halos of damped LyAlpha absorbers and the low N(H I) metal line absorption systems seen in the spectra of high redshift quasars. These ``C IV-HVCs'' present important opportunities for relating the properties of nearby intergalactic gas (or an extended Galactic halo) to the properties of gas in higher-z systems. Here, we request STIS spectra to study the ionization properties of C IV-HVCs along the PKS 2155-304 and PG 1116+215 sight lines. We will compare their properties with those of the C IV-HVCs toward Mrk 509 to test the hypothesis that these clouds are remnants from the formation of the Local Group. The results have implications for the origin of HVCs, the processes that distribute and ionize diffuse gas in the Local Group, the extent of the Galactic halo, and the interpretation of high-z quasar absorption line systems. ================================================================================ Proposal Category: GO Scientific Category: AGN PHYSICS ID: 8098 Title: Fe II emission lines as a chronometer for high-redshift quasars PI: Francis Keenan PI Institution: Queen's University of Belfast We request STIS observations of the symbiotic nova RR-TEL to give complete coverage of ionFe2 emission lines in the 1150--9800 Angstrom\ wavelength range. We have embarked on a long-term program to fully simulate the physical conditions within ionFe2-emitting gas, and predict the resulting spectrum. The first steps of generating the initial atomic database and incorporating it into the photoionization code Cloudy, are complete. Analysis of the ionFe2 lines from RR-TEL using Cloudy will allow us to check the reliability and completeness of the atomic data and processes considered, to investigate the sensitivity of emission to temperature and density variations, and to assess the importance of blending. Although emission lines from ionFe2 are observed from a wide variety of astronomical objects, including protostellar disks, novae, supernovae, and quasars, these lines have been notoriously difficult to interpret because of the great complexity of the Fe^+ energy level structure. We now have the tools to quantify the abundances in these objects and, once calibrated against the RR-TEL data, we will apply the same technique to deduce iron abundances from ionFe2 emission in high-redshift quasars. This, in conjunction with predictions of stellar evolution and galactic nucleosynthesis, will result in a chronometer measuring the redshift when the universe passed through an age of 1 Gyr, thus constraining several cosmological parameters. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8099 Title: Imaging the Circumstellar Environments of the Cool Hypergiants PI: Roberta Humphreys PI Institution: University of Minnesota The cool hypergiants are evolved massive stars that lie just below the empirical upper luminosity boundary in the HR Diagram, with spectral types ranging from late A to M. Our recent observations of two of these stars have yielded surprising results about their circumstellar environments including evidence for bi-polarity, equatorial disks, and multiple high mass loss events. To fully understand their mass loss histories, we need to sample these stars at a variety of stages during their brief evolution as cool hypergiants. We propose high resolution imaging of 8 of the most luminous known cool stars. The presence or lack of fossil shells, equatorial ejecta, jets and other structures in their circumstellar environments will be a record of their current and prior mass loss episodes. Each star has been selected on the basis of its infrared emission, strong molecular emission, or peculiar spectroscopic variations to give us a snapshot of different steps in their evolution across the top of the HR Diagram. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8100 Title: Calibration of Nearby Type Ia Supernovae as Standard Candles: The Next Step PI: Abhijit Saha PI Institution: National Optical Astronomy Observatories We propose to continue our calibration experiment for M( max) of type Ia supernovae (SNe Ia) by determining Cepheid distances to their parent galaxies. To date we have completed (citeic4182a -- citengc4639) the calibration for 6 SNe Ia, from Cycles 1, and 3 -- 5. Our results from Cycle 6 on a seventh SN Ia, SN 1989B in NGC 3627, are ready to be submitted citengc3627. Cepheid- calibrated luminosities of two additional SNe Ia have become available from external data. HST observations of NGC 4527 (SN 1991T) and a few test exposures of NGC 1316 (SNe,1980N and 1981D) are planned for Cycle 7. Although there are now a total of 9 SNe Ia with Cepheid-calibrated absolute magnitudes M( max) in B and V, resulting values of H_0 in the literature range from 55 citeschaefer98 to 69 citeMKF98. The discrepancy depends on the exclusion of some of the calibrators for various reasons, the inclusion of questionable objects, and/or differences in second-parameter corrections. The only way out of this dilemma is to obtain a statistically robust sample of SNe Ia with reliable Cepheid distances. --- We request 2 * 34 orbits during Cycle 8 for the discovery and two-passband photometry of the Cepheids in the two target galaxies NGC 3982 (SN 1998aq) and NGC 1316 (SNe,1980N and 1981D), based on 2 orbits each for 12 epochs in F555W and 2 orbits each for 5 epochs in F814W. ================================================================================ Proposal Category: GO Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8101 Title: High Resolution Imaging of the Core of Maffei 1, the Nearest Normal Massive Elliptical Galaxy PI: Ronald Buta PI Institution: University of Alabama We propose to obtain high resolution optical images of the center of the galaxy Maffei 1, which is the nearest normal intermediate to giant elliptical galaxy. Recent studies have shown that Maffei 1 is much larger (D_0 = 25^ ) and brighter (V_T^0 = 6.4) than previously thought, and that it is only 2.7 +/ - 0.6 Mpc distant. This is one-sixth the distance to the Virgo and Fornax Cluster ellipticals, and 1 pixel in the Planetary Camera (PC) field covers only 0.5--0.7 pc. Thus, with HST, we have the opportunity of studying the core of a normal massive elliptical galaxy (M_V = -20.7) at sub-parsec spatial resolution. Besides revealing the profile of light in the core, which is invaluable for assessing the extent to which dissipation affected evolution, our images will be used to search for evidence of a central concentration of mass, including an accretion disk that might surround a supermassive black hole. Because of the proximity of Maffei 1, we will be able to identify a central black hole of considerably less mass ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8102 Title: FGS astrometry of the extrasolar planet of Gl 876 PI: Thierry Forveille PI Institution: Observatoire de Grenoble We propose astrometric observations with FGS1R in POS mode to confirm the recent radial velocity detection of an extra-solar planet around the M4 dwarf Gliese 876, by a totally independent method, and to determine the actual mass of the planet without the unknown 1/sini factor of the radial velocity methods. This will be the first extra-solar planet whose mass is actually determined from first principles. ================================================================================ Proposal Category: GO Scientific Category: BINARY STARS ID: 8103 Title: A Global Picture of White Dwarfs in Cataclysmic Variables PI: Paula Szkody PI Institution: University of Washington During the past 6 yrs, we have demonstrated that UV spectra of 4 unique non- magnetic Cataclysmic Variables in quiescence provide accurate temperatures, rotation rates, chemical abundances of the photosphere and Einstein redshift masses of the accreting white dwarfs in these systems. We are now in a position to advance to a broader and deeper understanding of fundamental tangential accretion physics and a global understanding of the accreting white dwarf as a function of its evolutionary history by extending our analyses to 16 systems that are carefully selected to ensure detection of their underlying white dwarfs. Applying the STIS spectral advantages of high sensitivity and resolution to this large sample, we can refine the distribution of temperatures, rotational velocities and composition as a function of orbital period and system type, and determine the correlation of accretion belts with missing or weak boundary layers and anamolous compositions. The physical insights from these simplest and most observable systems should apply in the broader context of equatorial accretion flows onto central compact objects in a variety of disk accreting systems (T Tauri stars, X-ray binaries, disk accreting symbiotics, Algols with transient disks). ================================================================================ Proposal Category: GO Scientific Category: AGN PHYSICS ID: 8104 Title: Constraints on the Evolution of Powerful Radio Galaxies PI: Christopher O'Dea PI Institution: Space Telescope Science Institute Recent work has identified the GHz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources as the most likely candidates for the progenitors of the large scale powerful classical double (3CR FR2) sources. WFPC2 LRF images have revealed the presence of bright emission line gas aligned with and in projection co-spatial with the radio source. Ground based observations of broad and highly structured OIIILambda 5007 lines strongly suggest that the radio source is dominating the emission line kinematics. We propose to observe 3 CSS sources with STIS long-slit spectroscopy in order to determine the kinematics and physical properties of the emission line gas interacting with the radio source. We will use diagnostic line ratios to estimate the temperature and density of the gas. From the velocity field, we will derive constraints on the expansion velocity of the radio source and on the radio source lifetime, both of which are fundamental parameters needed to constrain the evolution of powerful radio sources. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8105 Title: Global Change on Pluto? PI: James Elliot PI Institution: Massachusetts Institute of Technology Pluto and Triton, two bodies that likely formed in the solar nebula (rather than a pre-planetary nebula), hold the promise of telling us much about early conditions in the outer solar system. Pluto and Triton are remarkably similar in size and density, and each suffered an early catastrophic event: Triton's retrograde orbit indicates that it was captured by Neptune, while Pluto's binding with Charon also required a large dissipation of energy. The low probability of such events for two isolated bodies implies that Pluto and Triton have remained from a much larger Kuiper belt population that existed in the past. Observation of a stellar occultation by last year with the FGS has shown that (i) Triton has been undergoing a period of global warming, and (ii) Triton has a much deeper troposphere than previously thought. A similar observation of an occultation by Pluto is proposed to probe whether it is undergoing global change as well. In addition to observing the occultation, we propose astrometric observations that will be critical for deploying portable telescopes and for interpreting Earth-based occultation observations, even if the HST proves not to be within the occultation path. ================================================================================ Proposal Category: GO Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8106 Title: The mass of the black hole in Cygnus A PI: Clive Tadhunter PI Institution: University of Sheffield, Although supermassive black holes are thought to be the main power source for the jets and active components of radio galaxies, the relationship between the masses of the black holes, the bulges of the host galaxies, and the radio activity are not understood with any certainty. Part of the problem has been the lack of suitable dynamical tracers in the nuclei of the radio source host galaxies. However, using HST imaging observations we have recently detected a high surface brightness disk structure at the centre of the archetypal powerful radio galaxy Cygnus A. We now propose to use STIS measurements of the emission line kinematics in the disk to measure the mass of the core of the galaxy, and thereby test the idea that powerful radio sources are only associated with the most massive black holes (M_bh > 10^9 M_\odot) in the host galaxies with the most massive galaxy bulges. Requiring only 5 orbits of HST time, this project is fundamental to our general understanding of the energy generation mechanisms in powerful radio galaxies. These observations will represent the first attempt to map the kinematics of the ionized gas in detail on a sub-kpc scale in a powerful FRII radio galaxy. Given the requirement for high spatial resolution long-slit spectroscopy across the core of the galaxy, this project can only be done with STIS on the HST. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8107 Title: What is the Nature of the Cold Medium in Cooling Flow Clusters? Clues from <~ PI: Christopher O'Dea PI Institution: Space Telescope Science Institute X-ray spectra of a significant fraction of cooling flow (CF) clusters of galaxies indicate the presence of large columns of ``cold'' absorbing material. The physical nature of the absorbing medium remains a mystery. Searches for H I in this medium using the 21 cm hyperfine structure line, and for molecular gas traced by CO yielded null results at the required levels. The LyAlpha absorption cross section is >= 10^7 times larger than for the 21 cm line, and it can therefore be used as a much more sensitive probe of H I in clusters. This method was applied to the Perseus CF cluster using a medium resolution (~ 250 km s^-1) HST spectrum, yielding an upper limit on the H I column about three orders of magnitude smaller than implied by X-ray spectra. We propose to obtain higher resolution (~ 40 km s^-1), spatially extended spectra of the Ly-alpha\ emission line filaments in three CF clusters with the brightest known LyAlpha fluxes. These spectra will allow us to probe H I columns about 10^7 smaller than deduced from the excess X-ray absorption in these clusters (>= 10^20 cm^-2), and thus put very strong constraints on the nature of the cold absorbing medium and its covering factor. If substantial amounts of cold gas do exist in the ICM, this would have important implications for our understanding of cooling flows, the physics of the ICM, galaxy formation and evolution, and LyAlpha forest systems. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8108 Title: Search for Origin of Supersonic Turbulence Observed in the Upper Equatorial Atmosphere of Jupiter PI: Claude Emerich PI Institution: CNRS-Institut d'Astrophysique Spatiale It is now clear that Jupiter, like the Sun, sustains a coronal region at the top of its atmosphere. H-Ly-alpha\ spectra measured by GHRS in the Jovian Ly- alpha\ bulge region, evidenced a non thermal line broadening, implying supersonic atomic motions and variability on a time scale of about one minute. Such an atmospheric turbulence was suggested by Ben Jaffel et al. 1993 to explain the Jovian Ly-alpha\ bulge by an enhancement of the H-Ly-alpha\ resonance cross-section rather than by a local increase of the H density. Sommeria et al. 1995 proposed then a model of thermospheric circulation reproducing the main characteristics of the bulge and explaining the heating excess observed in the Jovian upper atmosphere. This temperature excess was also explained by Yelle (1996) invoking heating from gravitational waves dissipation. To put new constraints on these models, and to find out potential alternative explanations, we propose to use STIS to make high- resolution H-Ly-alpha\ line profile maps in four crucial regions of the planet. Recent cycle 7 STIS auroral observations of J. Clarke et al., demonstrated its capability to provide a wealth of new information on spatial, spectral and scale height distributions, allowing to refine our understanding of the physical processes that drive this highly perturbed region of the Jovian atmosphere, using only a few HST orbits. ================================================================================ Proposal Category: GO Scientific Category: AGN PHYSICS ID: 8109 Title: Determination of the SED for TON S180: A Direct Probe of the Big Blue Bump PI: Jane Turner PI Institution: Goddard Space Flight Center The Seyfert 1 galaxy, TON S180, is the brightest AGN in the extreme UV regime, there is a low Galactic column along the line-of-sight and no evidence for intrinsic absorption. This offers a rare opportunity to obtain the spectral- energy-distribution (SED) of the source, including data from the vital soft X- ray to UV range which is generally difficult to observe due to absorption of those photons by Galactic material. TON S180 has a strong soft X-ray excess, and may be the best case in which to confirm the presence of a Big Blue Bump (BBB). The existence of a BBB in the EUV continuum is extremely controversial. For example, although the SEDs derived from QSO spectra appear to be power-laws, photoionization models based on these fits greatly underpredict the strength of the He II emission lines. This apparent deficit of He II ionizing photons could be explained if a BBB were indeed present. We request a STIS observation of TON S180, to be made simultaneous with our approved AXAF and FUSE observations. The combined data will allow us to determine the SED and test the presence of a BBB, addressing the photon deficit problem in detail. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8110 Title: Supernova Remnants in a Cloudy Interstellar Medium PI: You-Hua Chu PI Institution: University of Illinois Small cloudlets in the interstellar medium (ISM) may have a marked effect on the physical structure and evolution of supernova remnants (SNRs). The effects of evaporating cloudlets in a SNR interior have been modeled and are an important factor leading to McKee & Ostriker's three-phase model of the ISM. The cloudlets themselves are only now becoming observable through high- resolution instruments such as the Hubble Space Telescope's Wide Field and Planetary Camera (WFPC2). We propose WFPC2 observations of the three SNRs, N49, N206, and N63A, which appear to be the best candidates for the examination of the physical structure of SNRs in a cloudy ISM. These WFPC2 images can be combined with complementary observations in other wavelength regimes to identify cloudlets inside remnants; trace SNR shock fronts; determine the physical parameters of interior cloudlets and compare them to those of the hot interior; and investigate the evaporation of shocked cloudlets into the hot cavities of the SNRs. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8111 Title: CS 22892--052: A Rosetta Star for the Age and Early History of the Galaxy PI: Christopher Sneden PI Institution: University of Texas We propose to observe the ultra-metal-poor Galactic halo star CS 22892--052 and to produce the most complete abundance distribution of the heaviest stable elements, including platinum, osmium and lead, of any star outside of the Sun. These HST abundance data will then be used to estimate the initial abundance of the long-lived radioactive element thorium and, in comparison with its observed abundance, will be used to determine the age of this very old star. These studies, using radioactive chronometers in stars, provide an age estimate for the Galaxy independent of globular cluster and cosmological ages. Our proposed observations of CS 22892--052 will also provide significant new information about the early history of the Galaxy, specifically the nature of the earliest generations of stars and the types of nucleosynthetic processes that occurred in those stars. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8112 Title: Probing the Galactic Halo and Beyond with Young Supernovae PI: George Sonneborn PI Institution: NASA/Goddard Space Flight Center We propose a Target of Opportunity program to obtain STIS echelle spectra of a bright new supernova (V<14) to characterize the ionization state, gas-phase abundances, depletion on dust grains, metallicity, and gas kinematics in the Galactic halo, the ISM and halo of the SN's host galaxy, and, if the properties of the sightline are favorable, in the intervening intergalactic medium. The principal spectral region for this study is the far ultraviolet (\wl <1700Angstrom), which provides a comprehensive set of lines to study the hot, warm, and cool phases of the ISM. Near-UV spectra will provide Zn II and Cr II line profiles with which to assess gas-phase depletion. New core- collapse supernovae, with their strong, nearly featureless UV continua, provide outstanding opportunities to obtain high-quality absorption line spectra of the gas on the line of sight to the SN, but only if the observations are executed within ~2 weeks of outburst. Our team has the experience and extensive ground-based support to rapidly assess the suitability of each newly-discovered supernova for this program and provide all the necessary data to efficiently implement the proposed observations, as demonstrated by our successful low resolution observations of SN 1998S in Cycle 7. ================================================================================ Proposal Category: SNAP Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8113 Title: Dust and Ultraviolet Light in the Local Universe PI: Marie Treyer PI Institution: Astrophysikalisches Institut Potsdam Ground-based spectroscopy of a flux-limited sample of galaxies imaged at 2000 Angstrom\ with the FOCA balloon-borne camera has allowed us to derive a new estimate of the local star formation rate (SFR) in a manner directly comparable to that utilised for high redshift galaxies (Treyer et al. 1998). Although UV radiation is a more sensitive tracer of instantaneous star formation than optical light, the inferred SFR is significantly more sensitive to unknown effects of dust scattering and absorption. Even modest dust corrections would imply the strong evolution claimed in the 099\ about a dozen distinct frequencies (0<=\ell<=2). These frequency measurements will enable us to determine stellar mass, age, and helium abundance, while refining existing measurements of other parameters. Hipparcos parallaxes coupled with a detailed spectroscopic analysis will overconstrain stellar models, allowing a test of the underlying physics (the onset of core convection, for example). This study will herald a new era of practical asteroseismology, and serve as a benchmark for future space missions dedicated to stellar seismology. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8116 Title: Spectroscopy of the Rapidly-Evolving, Chemically Inhomogeneous Planetary Nebula BD+30 3639 PI: J. Patrick Harrington PI Institution: University of Maryland BD +30^degrees3639 is one of the most important and extensively observed of all planetary nebulae. One of the few PNe with X-ray emission from the shocked stellar wind, it is an approved AXAF target. ISO observations led to the unexpected discovery of crystalline silicates in this carbon-rich nebula. This, and other evidence, shows that BD+30 has undergone rapid chemical evolution, and is likely to show abundance anomalies and gradients in the ionized gas. We propose to obtain several long-slit near-UV and optical spectra of BD+30. This will enable us to map the C/O ratio with high spatial resolution (~ 0.2"). We will also obtain co-spatial determinations of the temperature and density, map the behavior of the enigmatic C II 4267 recombination line, and perhaps track the Si/C ratio. We propose 2nd-epoch observations to our earlier (1994) WFPC2 images to measure the angular expansion. To map the velocity field of BD+30 -- crucial to get its distance from the angular expansion -- we will take echelle spectra in the C II Lambda2326 line. Such detailed mapping is necessary in light of the discovery of high-velocity outflows, not only in molecular gas (CO, H_2), but even optical lines. These observations will complete a comprehensive picture of a PN which can open a window onto the final dredge-up and mass-loss phase of AGB evolution. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8117 Title: Saturn's FarUV Aurora and Polar Hazes PI: John Trauger PI Institution: Jet Propulsion Laboratory We propose to carry out a coordinated program of STIS imaging and spectroscopy in the FUV and NUV during one full rotation of the planet in order to capture a complete picture of the south auroral emission region on Saturn. FUV imaging and chapman-profile modeling is our lever to characterize emissions from above the homopause, while FUV and NUV spectroscopy and radiative transfer modeling will describe the atmospheric phenomena driven by particle radiation that penetrates below the homopause. The proposed observation is a direct extension of a program of WFPC2 and STIS imaging begun in Cycles 6 and 7. Very little is presently known about the range of possible morphologies and temporal behaviors in the Saturn aurora. One complete rotation is required to sort out the planet-fixed and local-time-fixed characteristics, and to provide spectra with sufficient S/N to reliably constrain the radiative transfer modeling. ================================================================================ Proposal Category: SNAP Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8118 Title: A Snapshot Survey of Galactic Globular Clusters PI: Giampaolo Piotto PI Institution: Universita di Padova HST observations of crowded centers of globular clusters (GCs) have produced intriguing discoveries of new phenomena, most of which are not understood theoretically. We propose here a continuation of a Cycle 7 snapshot proposal, to extend such work to a much larger portion of the Galactic GC system. Up to now <20\ observed, with results that have been so fruitful that we propose to complete the original target list, continuing to observe the centers in B and V with WPFC2. We request a proprietary period of only 3 months. Our color- magnitude diagrams will include all stars down to ~ 1^ m below the main- sequence turnoff, allowing us to address many outstanding questions, such as: How does the frequency of confirmed or suspected stellar interaction products e.g., blue stragglers, horizontal branch (HB) tails depend upon the local stellar density and the cluster dynamical state? How common are the strange HB morphologies recently discovered by HST in several GCs, and are they confined to the central regions? How often do metal-rich GCs have a hot HB, and does it correlate with the cluster dynamics? We will also improve the core parameters for a number of GCs, and constrain their dynamical states. This survey will produce a fundamental data set of Galactic GCs, which will be useful for a large number of studies in the years to come, and be a part of the legacy of HST. ================================================================================ Proposal Category: GO Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8119 Title: Measuring the black hole mass in Centaurus A, the nearest active galaxy PI: Ethan J. Schreier PI Institution: Space Telescope Science Institute We will use STIS to measure the mass of the black hole at the center of NGC5128 (Cen A), the nearest active galaxy. The presence of a super-massive black hole, comparable to that of M87, is suggested by the jet, the extent of the radio lobes, and the presence of strong nuclear radiation extending to hard X-rays and Gamma-rays. A 1" (~ 17pc) radius ionized accretion disk at the nucleus of Cen A was discovered in PaAlpha using HST NICMOS (Schreier et al. 1998); we have now (1998 August) also seen the disk in Fe IILambda1.643Mu m. Recent near-IR ground based spectra (Blum, 1998 private communication) reveal broadened lines near the nucleus, consistent with a central mass ~eq 10^9 M_\odot. These and other observations demonstrate that notwithstanding the high dust extinction at the center of NGC5128, a number of lines in the ~eq0.9 -2.2Mu m range can be used to study the mass distribution. HST's spatial resolution is required to yield a good mass determination. S IIILambda 9532Angstrom\ is the shortest wavelength line which is seen to be present and is readily accessible to STIS. Observing with the G750L low-dispersion grating of STIS through the 0arcs1 wide slit, we will thus use the S III emission line as a gas tracer to measure the rotation curve of the disk, measure the mass distribution in the central few parsecs of the galaxy, and determine the mass of the black hole. ================================================================================ Proposal Category: GO Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8120 Title: Determination of Circumstellar Cloud Mass Loss Rates with STIS Spectra PI: C. R. O'Dell PI Institution: Rice University We propose to resolve the question of whether or not the circumstellar disks around young low mass stars in clusters containing O type stars are rapidly destroyed by photoevaporation. The answer will determine whether or not the conditions necessary for planet formation are common or rare in the massive star clusters where most stars are created. At the present there is a conundrum arising from the fact that most of the circumstellar disks survive in the Orion Nebula Cluster even though the theoretical models predict that the intense radiation field should have destroyed them in times short compared with the estimated age of the cluster. We propose to obtain STIS high resolution spectra which will allow direct measurement of any photoevaporative flow off disks around two young low mass stars near \tc\ Ori. These results will test existing theories for photoevaporation and directly tell us how long these disks can survive. Only the HST and STIS have the right combination of spatial and spectral resolution to adequately reject the contaminating light from the Orion Nebula itself and allow clear determination of the emission coming from the young stellar object. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8121 Title: Proper Motions and Variability of HH Objects Near the Orion Nebula PI: C. R. O'Dell PI Institution: Rice University The Orion nebula possesses at least three systems of HH objects, each with very different characteristics. No other source shows such a variety of outflow phenomena, and we seek to understand why this is so. An essential parameter in understanding these systems and the individual shocks is their spatial motions. A recent groundbased Fabry-Perot study has provided radial velocities for all of the brightest members, but proper motion information is uncertain and available for only a few. The existence of earlier WFPC2 images presents an opportunity to produce accurate proper motions through repeating those observations in Cycle 8. The proposed observations will clarify how shocks sweep up material in the dense H II and Photodissociation Regions, and pinpoint locations of photometric variability within the shocked cooling zones. The timing for this is optimal since the sample of current proper motions indicates that the 4.7-6.0 year time interval will allow accurate results; the results should be obvious and unambiguous. By rotating the field for one of the pointings we'll be able to obtain the first HST images in O I and S II in one of the richest regions of the nebula. The product of this investigation will be proper motions and temporal variability for all of the HH objects in the region, and an O I and S II survey of an unstudied region. ================================================================================ Proposal Category: GO Scientific Category: FIELD STELLAR POPULATIONS ID: 8122 Title: The evolution of galaxies -- mining the stellar content of the two most local Blue Compact Dwarf Galaxies PI: Regina Schulte-Ladbeck PI Institution: University of Pittsburgh We propose to exploit the unique, high spatial resolution of the WFPC2 to obtain deep color-magnitude diagrams (CMDs) of two newly recognized very nearby (D<3 Mpc) blue compact dwarf galaxies (BCDs). The CMDs will be modeled to extract the star-formation histories; in particular, we will use red-giant stars to determine WHEN these galaxies first started to make the bulk of their stellar population. This will provide an important alternative to galaxy counts for testing the predictions of dwarf galaxy evolution. BCDs are very small, nearby, starbursting systems which (at least in some cases) also contain an older stellar population. The star-formation history of BCDs is a key to understanding the enigmatic evolution of dwarf galaxy populations -- for example, the faint blue excess, thought to be due to low-mass galaxies experiencing a short epoch of star formation at redshifts 0.5m_\odot; (4) measure the rotation of the cluster in the plane of the sky; (5) measure the absolute proper motion of the cluster; and (6) possibly measure the proper motion of the Small Magellanic Cloud. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8161 Title: Boron in the Magellanic Clouds: A Novel Test of Light Element Formation PI: Kim Venn PI Institution: Macalester College Observations of boron abundances in the Magellanic Clouds will provide a novel test of the assertion that boron is produced primarily through spallation reactions between cosmic rays and ambient interstellar nuclei. The lower metallicities and especially the lower cosmic ray flux of the Small Magellanic Cloud, as inferred from Gamma--ray observations, imply that, if spallation is the dominant production mechanism, boron should be significantly underabundant in the Clouds relative to its local Galactic value. Only spectroscopy from space can provide the necessary boron abundances. In this proposal, we are requesting HST STIS observations to detect the B III resonance lines in one LMC and two SMC main-sequence B stars. Only STIS can observe these NUV lines, especially with the resolution and S/N required for reliable boron abundance determinations. The main-sequence stars selected for this project show no signs of stellar mixing (which could destroy B), thus they can be used to determine an accurate, present-day, boron abundance. This abundance will be compared with that predicted by simple models of galactic chemical evolution using the inferred cosmic ray fluxes and interstellar abundances of target nuclei. ================================================================================ Proposal Category: GO Scientific Category: DISTANT GALAXIES ID: 8162 Title: Identifying the hidden phases of galaxy evolution PI: Simon Lilly PI Institution: Department of Astronomy, University of Toronto Deep surveys in the sub-mm waveband are revealing a population of very luminous dusty galaxies at high redshifts, 0.5 < z < 3, which are; (a) as a population, producing stars at a rate as large or larger than the optically selected galaxy population at high redshifts and thus presumably producing a substantial (and perhaps dominant) fraction of all stars that have ever been produced; and (b) doing so, individually, in systems with bolometric luminosities (i.e. star-formation rates) that are very much larger than typically seen in the optically-selected population. Together, these suggest that the sub-mm sources represent a major phase of galaxy evolution that is not represented in the optically-selected samples. We are engaged in a major study of this population using SCUBA on the JCMT. Existing HST images are playing a crucial role in this work - both in revealing disturbed morphologies of the identifications and in simply identifying the optically faintest sources. But at present our HST images only cover a modest fraction of our two main survey areas, limiting the number of sub-mm sources that can be identified and studied in detail. We propose to observe additional fields in our survey areas to overcome this limitation. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8163 Title: Trapezium Systems and Stellar Jets in 30 Doradus PI: Nolan R. Walborn PI Institution: Space Telescope Science Institute 30 Doradus is the nearest and best resolved extragalactic starburst, hence a paradigm for the phenomenon. Recent NICMOS observations of the new stellar generation being triggered by the outflows from R136 establish 30 Dor as a prime region for investigation of massive-star formation as well. Since 1"\ already subtends 50,000 AU at 50 kpc, HST makes unique contributions to the study of 30 Dor. A recent groundbased spectral-classification study has provided new insights into the stellar content of 30 Dor, but many of the targets are resolved into multiple systems in the available WFPC2 images. We propose to obtain spatially resolved STIS blue spectroscopy of some of the newly found multiple systems, which is essential to determine accurate stellar tempertures and masses. Several systems each in the new and previous stellar generations are included. The HST spatial resolution also reduces the contamination of the stellar spectra by the nebular emission lines, which is a critical advantage. We also propose dithered PC nebular-line images of the young Trapezium systems Knots 1-3, which interact strongly with the surrounding interstellar medium, forming several parsec-scale jets. Finally, we shall do two WFPC2 pointings with continuum filters, to complete the coverage of the field, which currently limits the search for multiple systems and the illuminating comparisons with IR and other data. ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8164 Title: A Search for Intergalactic Globular Clusters in A1185 PI: Michael J. West PI Institution: Saint Mary's University The origin of the anomalously rich globular cluster populations surrounding many supergiant elliptical galaxies remains one of the great unsolved problems in the study of extragalactic globular cluster systems. A number of authors have suggested that the intrinsic globular cluster populations of such galaxies may have been augmented by large numbers of intergalactic globular clusters which are not bound to individual galaxies but, instead, roam freely throughout the cores of clusters of galaxies. Although there is now considerable circumstantial evidence in support of this view, efforts to detect intergalactic globular clusters directly have thus far been thwarted by the complication that most galaxy clusters have a supergiant elliptical galaxy residing at their dynamical centre, which makes it impossible to separate bona fide intergalactic globulars from the galaxy's own intrinsic population. To avoid this difficulty, we propose to search for intergalactic globulars in the rich, nearby cluster Abell 1185, since its brightest member galaxy is offset from the X-ray centroid by ~eq 4^ (150 kpc). A series of deep WFPC2 images centered on the peak of the X-ray distribution in Abell 1185 should reveal a population of intergalactic globular cluster if it exists. The detection (or non-detection) of such globular clusters will provide important new constraints on galaxy interactions and evolution in clusters. ================================================================================ Proposal Category: GO Scientific Category: QUASAR ABSORPTION LINES ID: 8165 Title: Pervasive Hot Gas Hidden in Galaxy Groups: A Substantial Baryon Reservoir? PI: Edward Jenkins PI Institution: Princeton University Observatory We propose to use STIS to search for hidden and pervasive hot gas in the intracluster media of groups of galaxies. Cosmological simulations predict that at z ~ 0, most groups of galaxies should be embedded in large filaments and sheets of shock heated gas at 10^5 -- 10^6 ^degreesK. This hot gas may contain a substantial fraction of the baryons in the universe at the present epoch, but its quantity and existence is not firmly established because gas in this temperature range is difficult to detect in x-ray emission. However, it can easily be detected via absorption lines of highly ionized species such as O VI. We propose to observe H1821+643 and PG1116+215 to search for O VI and broad H I LyAlpha absorption due to the intracluster media of thirteen known galaxy groups pierced by the sight lines. Toward H1821+643, we have already discovered O VI absorption associated with a galaxy group at z = 0.225 using low resolution HST GHRS spectra, but we could not determine if the O VI absorber is collisionally ionized or photoionized. With the vastly improved resolution and sensitivity provided by STIS, we will be able to identify the ionization mechanism in this absorber by (1) searching for broad H I absorption in collisionally ionized gas or narrow H I indicative of photionized gas, (2) measuring C II/C III/C IV and Si II/Si III/Si IV, and (3) examining the velocity widths of low and high ionization stages. ================================================================================ Proposal Category: GO Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8166 Title: WFPC2 Narrow--Band HAlpha Imaging of the Edge-on Galaxy NGC4631 PI: Q. Daniel Wang PI Institution: Northwestern University Observations of nearby edge-on disk galaxies are essential to determine the role that the disk/halo interaction has in galaxy evolution. Located in a direction of exceptionally low Galactic extinction, NGC4631 is particularly suitable for a multi-wavelength investigation of extra-planar gas components. In fact, NGC4631 is one of the most well studied late-type disk galaxies. Broad-band optical, near-infrared, near-UV, and far-UV observations have been (or will be) taken with HST\ and \fuse. We have obtained \axaf\ observing time to conduct a spatially-resolved X-ray spectroscopic observation of the galaxy. Here we propose for HST\ WFPC2 narrow--band H-alpha\ imaging of the galaxy's active central region. This image will enable us to resolve various narrow filaments of warm ionized gas that extend more than 2 kpc away from the mid- plane of the galaxy. Based on the geometry, filling factor and line intensity of the filaments and their correlation with X-ray-emitting gas, we will study their origins (chimney walls, blisters, condensations of cooled hot gas, shocks, etc). The results will be invaluable for our understanding of similar extra-planar gas observed in the Milky Way and other galaxies. ================================================================================ Proposal Category: GO Scientific Category: DISTANT GALAXIES ID: 8167 Title: WFPC2 Imaging of a Galaxy at z = 5.34 and its Field PI: Daniel Stern PI Institution: University of California, Berkeley We propose to obtain deep WFPC2 images of a galaxy at z=5.34 and its surrounding field. The galaxy, 0140+326 RD1, was the first spectroscopically confirmed object at z > 5 and among the few confirmed objects at z > 5 currently. Our goals are to (1) map the Ly-alpha line--emitting region, (2) study the restframe UV continuum morphology, (3) search for companion Ly-alpha --emitting sources, and (4) study the stellar population and dust extinction in this distant system in conjunction with recently obtained NICMOS F160W images. If this galaxy is a truly primeval object in the process of forming its first generation of stars, its morphological properties can provide critical information on the earliest phases of galaxy formation. Ongoing, deep, multi--wavelength, ground--based efforts make this an ideal field for HST to underlinesimultaneously provide high--resolution morphological information on several other timely issues in extragalactic astronomy: the proposed WFPC2 pointing contains several sub--mm sources detected in a deep (~ 40 ksec) program with SCUBA; the most distant known radio galaxy, 6C 0140+326 at z=4.41; 2 confirmed and several candidate Lyman--break galaxies at z ~gt 4; and several unusually red galaxies. The observations proposed here cannot be accomplished from ground--based facilities, as their success depends upon the high spatial resolution and low sky background only attainable with HST. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8168 Title: The Optical Counterpart of the Soft Gamma-ray Repeater 1900+14 PI: Shri Kulkarni PI Institution: California Institute of Technology The soft gamma-ray repeaters (SGR), of which only four are known, are likely an exotic class of neutron star known as magnetars with ultra-strong surface magnetic fields (10^14-10^15 G). We have recently detected a radio synchrotron nebula or "afterglow" toward SGR 1900+14 which is powered by the particle outflow that accompanied a period of intense high energy bursting activity. The discovery of this afterglow has allowed a sub-arcsecond position to be determined for this source. HST observations are essential to overcome the crowding which is present along this line of sight. We request STIS time to identify the optical counterpart of SGR 1900+14 in hopes that it may shed further additional light on the fascinating SGR phenomena. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8169 Title: HST-Galileo Io Campaign PI: Fran Bagenal PI Institution: University of Colorado Io plays a central role in the Jovian system, yet the mechanisms that couple its volcanoes, the tenuous \sots atmosphere, the escaping corona and the plasma torus remain elusive. In 1999 there is the unique opportunity to combine HST observations with the Galileo close flybys of Io. A team comprising 40 experienced Io observers, modellers and theorists have come together to propose a campaign of HST observations that will address 4 critical issues concerning Io's enigmatic behavior: 4 pt noindento What do the compositions of plumes and surface deposits reveal about Io's volcanism? noindento How is Io's SO_2 atmosphere affected by volcanic activity? noindento How does Io's atmosphere interact with the surrounding plasma environment? What are the unidentified atmospheric emitters detected by Galileo? noindento What powers the Io torus emissions? 4 pt The team proposes an observing campaign of 12 targets over 35 HST orbits using WFPC2 and STIS to address these 4 tasks. On their own these HST observations will answer many issues of the emissions from Io's surface and plumes, atmosphere, corona and plasma torus. The synergy of combined HST and Galileo observations provides a powerful scientific opportunity that will not be repeated in the foreseeable future. ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8170 Title: Kinematics of the Young Star Clusters and the Gas in the Antennae Galaxies PI: Bradley Whitmore PI Institution: Space Telescope Science Institute We propose to follow up on our discovery of over 1000 young star clusters in ``The Antennae'' (NGC 4038/4039) by obtaining long-slit and slitless spectra of a representative sample of clusters with STIS. These young clusters have the luminosities, colors, and radii expected of young globular clusters and must have formed during the ongoing merger. Because of their proximity and early stage of merging, the disks of NGC 4038/4039 form an ideal laboratory to study cluster formation in progress. While we have GHRS spectra of two bright clusters, the greater sensitivity and two-dimensional capabilities of STIS will allow us to systematically study the kinematics of the stellar and gaseous components at unprecedented spatial resolution over a large fraction of the galaxy. In particular, we will be able to determine whether the velocity dispersion of the clusters increases with age, as would be expected as the process of ``violent relaxation'' turns two disk systems into an elliptical galaxy. In addition, more accurate measurements of ages from the long-slit spectra will provide an important consistency check on our earlier work using UBVI photometry and H Alpha\ imaging, and will make a variety of new studies possible (e.g., a search for evidence of propagating star formation). ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8171 Title: HST Far-UV Imaging and Spectra of Jupiter's Aurora During the Galileo Extended Mission PI: John T. Clarke PI Institution: University of Michigan This proposal is for far-UV imaging and spectroscopy of Jupiter's auroral emissions concentrating on the nature of the satellite auroral footprints in Jupiter's atmosphere. These observations will be scheduled close in time with Galileo spacecraft measurements of Jupiter's magnetospheric properties and UV emissions during the GEM mission's final orbits through 1999. In our cycle 7 program to study Jupiter's aurora, we have recently identified 1) an extended trail of auroral emission in the wake region beyond Io's magnetic footprint, and 2) auroral emissions from Ganymede's magnetic footprint on Jupiter. Given the emphasis of the GEM mission on the major satellites, we plan to concentrate in cycle 7 on more detailed studies of the electromagnetic interactions between the satellites and Jupiter. The images that we will obtain will also allow us to continue our study of Jupiter's auroral morphology, including updating the magnetic field model and studying dynamic behavior reflected in persistent latitudinal motions of the auroral oval in the morning and afternoon sectors. Because Galileo can only obtain limited dynamic range images of the visible nightside aurora under special circumstances, the HST observations are key to the interpretation of the Galileo magnetospheric and auroral data. ================================================================================ Proposal Category: GO Scientific Category: QUASAR ABSORPTION LINES ID: 8172 Title: STIS Deep DLA Imaging Survey II PI: Palle M\oller PI Institution: European Southern Observatory, Garching Using STIS we will obtain deep images of 20 high--z damped Ly-alpha galaxies at 1.86, as close as 0.4" (~ 1.4 h^-1 kpc) to the quasar line of sight. The damped Ly-alpha galaxies contain nearly all neutral gas in the Universe, so at high redshift they are the reservoirs from which today's stars formed. However quasar absorption--line studies do not provide sizes or morphologies, so they could be either large disks, or small e.g. more numerous proto--galactic subunits. Deep imaging can resolve this issue, and HST is required because the galaxies are very faint, and lie typically within 1" of the quasar. Our STIS survey is aimed at measuring impact parameters, UV continuum sizes, and star--formation rates of high--z DLA galaxies. With NICMOS we extended this study to the near--IR with deep H--band imaging of 20 DLA galaxies. These observations will provide the crucial rest--frame UV-- optical colors and optical sizes and morphologies. This proposal is to now complete STIS imaging of the NICMOS sample. The HST imaging together with ground--based spectroscopy will unify absorption--line studies and faint galaxy imaging studies, providing a comprehensive picture of the history of assembly, star formation, gas consumption, and chemical enrichment in the DLA galaxies. ================================================================================ Proposal Category: GO Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8173 Title: Alignment and evolution of redshift one radio galaxies PI: Philip Best PI Institution: Sterrewacht Leiden vspace*-2mm The galaxies associated with powerful distant radio sources are the most massive ellipticals known at early cosmic epochs, and are also uniquely important for understanding the physics of AGN and the interactions between the radio source and its environment. Our HST observations of a complete sample of powerful 3CR radio galaxies at redshift z ~ 1 reveal detailed small--scale structures aligned along the radio axis of these sources. In combination with deep emission line studies, we have shown that the properties of the host galaxies change dramatically throughout the lifetime of the radio source, being dominated in the small sources by the effects of the shocks associated with the radio activity. To allow quantitative measurements of the on-going physical processes and the nature of the surrounding environment, the importance of the radio beam power must be determined. To tackle this issue, in cycle 6 we began a project using WFPC2, imaging 5 galaxies from a complete subsample of 11 lower radio power 6C sources. The first results show that the 6C galaxies also possess aligned optical emission, but at lower flux densities than the 3CR galaxies. Comparison with our new VLA data shows radio--optical correlations on kpc scales. We now propose to finish the WFPC2 observations of our complete VLA subsample. This larger sample of galaxies over a wide range of radio sizes will allow an investigation of the evolution of the host galaxy properties following the passage of lower power radio jets. ================================================================================ Proposal Category: GO Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8174 Title: Internal Velocity Distribution in Globular Clusters, II PI: William van Altena PI Institution: Yale University We propose to determine the internal velocity distribution of the globular clusters NGC 6205 (M13) and NGC 6656 (M22) in their cores and, for NGC 6656, as a function of distance from the cluster center, and thus also infer its mass distribution. In addition to measuring the velocity dispersion and any anisotropy to 1 km s^-1 for various classes of stars, ( e.g. giants, dwarfs, blue stragglers), we hope to better quantify the suspected rotation (and hence cluster inclination) apparent in both of these clusters' radial velocity data. We will also derive kinematic distances for the two clusters by comparison to existing radial velocity data. These distances would be good to 1-3\ if the radial velocity data were of the expected accuracy of the proper motions. Instead, we will be limited by the radial velocities to 6\ accuracy, which should still have considerable impact on the derived luminosities of the RR Lyrae stars and their role in the cosmological distance scale. The HST Astrometry Science Team obtained GTO first-epoch exposures of the above clusters and three others (NGC 104, NGC 6752, and NGC 7078). The HST AST and its collaborators were granted Cycle 7 GO time to observe these latter three clusters and those observations are currently pending. In this proposal, we are requesting second-epoch exposures under GO time for the remaining two clusters, NGC 6205 and NGC 6656. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8175 Title: A Survey of Gravitational Lenses as Cosmological Tools III PI: Emilio Falco PI Institution: Smithsonian Astrophysical Observatory Gravitational lenses are powerful tools for studying cosmology, galactic structure, and galaxy evolution. Such studies require large, uniform sets of photometric observations and must be conducted from space because typical image separations are ~1". CASTLES ( CfA- Arizona- Space- Telescope- LEns- Survey) is an ongoing survey of known lensed systems. Some of its goals are: to create a complete, uniform high-resolution photometric sample of the known galaxy-mass lenses; to obtain redshift estimates for all lens galaxies which lack spectroscopic redshifts; to find any source or lens components that have escaped detection and determine their photometric properties; to obtain precise astrometric data for all source components to improve lens models and estimates of H_0; and to investigate the wide field environments of the lens galaxies and their role in lensing. We propose to obtain WFPC2 V and I images of the 14 new lens systems discovered after previous CASTLES proposals; to re- image 13 lens systems with inadequate non-CASTLES observations; to image 2 systems that were excluded from CASTLES due to orbit cutbacks; and to obtain WFPC2 I images of 5 binary quasars. We again would waive any proprietary period for our data. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8176 Title: Confirmation and Characterization of Brown Dwarfs and Giant Planets from NICMOS 7226/7227 PI: Glenn Schneider PI Institution: University of Arizona A systematic search for giant planet and brown dwarf companions to stars in the solar neighborhood is a cornerstone of the NICMOS IDT's Environments of Nearby Stars (EONS) program. A carefully selected candidate list of 74 stars is currently being observed using the NICMOS coronagraph at 1.6Mum. We have found 8 objects as faint as H=20, up to 13 magnitudes fainter than their primaries with separations less than 5", which have very high probabilities of being true substellar companions. For the stars in our sample this covers minimum physical separations of 1.2-50 AU at the inner spatial detection limit. The lower mass limit depends on age, distance, and spectral type, but is as low as 3-5 M(Jupiter) for many of our targets. We are now requesting time for critical spectrographic observations to characterize the physical nature of the putative companions we have discovered. Our proposed observations will address fundamental questions such as: Is there a continuity of objects across the substellar mass spectrum bridging the main sequence to planetary objects? What is their frequency of occurrence? At what distances are they found from their primaries? And, what implications will these discoveries have for our understanding of stellar/planetary formation mechanisms? ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8177 Title: Investigating Type Ia Supernovae and an Accelerating Universe PI: Brian Schmidt PI Institution: Mt. Stromlo & Siding Spring Observatories The results from the high-z supernova groups that the Universe is accelerating rests entirely on the observation that the distant SN Ia are 0.25 magnitudes fainter than expected for an empty Universe. While both groups have argued that this magnitude offset is not due to quantifiable systematic effects, it is critical to test this assumption in new ways. We propose to use WFPC2 to obtain rest frame U and B photometry for four z~ 0.85 SN Ia. These observations will be coupled to ground-based rest frame V photometry and spectra. These data, combined with previous samples, will extend the D_L vs. z diagram for SN Ia to z~0.85, and allow us to discriminate the redshift dependence of supernova apparent magnitudes in an accelerating Universe from that expected to result from systematic effects such as age of the stellar population, chemical evolution, a drift in the properties of dust, and weak gravitational lensing. Evolution of SN Ia is a primary concern and it is only by careful object by object comparison that subtle effects will be apparent. We therefore also propose to use WFPC2 to obtain rest frame B and V photometry for four z~ 0.5 SN Ia. These data will be combined with extensive Keck spectra and rest frame U and R photometry obtained from the ground. The four z~ 0.5 objects will have light curves and spectra of comparable quality to nearby SN Ia, and will provide a basis for a detailed comparison. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8178 Title: Tracking the Evolution of the Homunculus and Outer Debris in Eta Carinae PI: Jon A. Morse PI Institution: University of Colorado We request Cycle 8 and Cycle 10 WFPC2 images of Eta Carinae in order to track the expansion of high-velocity material ejected during one or more giant outbursts of the central supermassive star. These images will increase the time baseline from 2 to 6 years of high-resolution Planetary Camera data for measuring proper motions and monitoring photometric changes in the debris field. Assuming a distance to Eta of ~ 2300 pc, we will be able to trace transverse motions of the debris of \ltsim 20 km s^-1 with the full 6 year time baseline. PC1 images in red and blue continuum filters will be used to track the expansion of the dusty bipolar lobes of Eta's ``Homunculus'' and equatorial skirt of ejecta. WF3 emission-line images will be used to trace motions of the outer debris field ~ 10'' - 40'' from the central star. This investigation will resolve the recent controversy surrounding the kinematic ages of the Homunculus lobes versus the equatorial skirt; whether or not these structures are co-eval has enormous implications for models of the outburst that created the Homunculus. We also can uniquely address issues of hydrodynamic expansion and wind-wind interactions through a time series of exposures of this textbook bipolar system. Because many groups around the world who are working on different facets of Eta Carinae will be interested in these images, we waive the proprietary rights to the dataset in order to maximize its usage. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8179 Title: THE COMPOSITION AND EVOLUTION OF EXTREMELY HOT DA WHITE DWARFS PI: Martin Barstow PI Institution: University of Leicester We propose high S/N (15:1 to 30:1) STIS far UV observations of the hottest known DA white dwarfs. With temperatures in the range 70,000-130,000K, these stars represent an important but little understood link between the H-rich central stars of planetary nebulae (CPN) and the general population of DA white dwarfs. Stellar temperatures are extremely difficult to determine in this range and depend upon knowledge of the photospheric composition, which is also a mystery. Consequently, their relationship to the cooler DA stars remains undefined. Far UV measurements of the abundances of heavy elements are essential for an ultimate determination of the stellar temperature. Coupling STIS data with an analysis of the Lyman lines obtained with planned FUSE observations, it will be possible to determine the physical parameters of these objects and finally track their evolution along the DA cooling sequence. In addition, we will search for evidence of mass outflow, in the form of blueward asymmetries in the heavy element line profiles, which is believed to cause departures from the compositions predicted by radiative levitation theory but which has been observed in only two DA white dwarfs. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8180 Title: The Lyman continuum radiation from galaxies PI: Jean-Michel Deharveng PI Institution: Laboratoire d'Astronomie Spatiale The amount of ionizing radiation released into the intergalactic medium by star formation is a poorly known but crucial parameter. This parameter would tell how the galaxies can complement the contribution of quasars for ionizing the IGM, especially at the epoch of re-ionization when the number density of quasars appears to decline. Direct measurements of the Lyman continuum radiation from galaxies are difficult and scarce. Indirect evaluations using models or theoretical arguments are plagued by the uncertainties on the Lyman continuum (\Lyc) escape fraction. We would like to take advantage of the ultraviolet sensitivity of the G140L grating of STIS to detect (or set significant upper limit on) the \Lyc\ radiation of star-forming galaxies in the redshift range 0.35 -- 0.6. We have selected four objects with an H Beta\ flux (or equivalent) that warrants the detection of a \Lyc\ escape fraction as low as 5\ ================================================================================ Proposal Category: SNAP Scientific Category: HOT STARS ID: 8181 Title: Resolving Sirius-like Binaries PI: Martin Barstow PI Institution: University of Leicester Space-based UV and EUV surveys have revealed a new population of detached binary systems, comprising main-sequence primaries that dominate the optical light, with hot white-dwarf secondaries that are revealed only at short wavelengths. We propose a snapshot survey in order to search for resolved, Sirius-like systems among these candidates. Subsequent determinations of the visual orbits of the resolved binaries with HST will provide dynamical measurements of the white-dwarf masses. Since there are only a very few dynamically determined white-dwarf masses at present, this programme could lead to a doubling or tripling of the number known. As a result, this sample will yield direct observational data on the white dwarf mass-radius and initial-mass ash final-mass relations and provide important tests of the respective theoretical models. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8182 Title: The Extent of Metal Transport in the Low Redshift Intergalactic Medium PI: John Stocke PI Institution: University of Colorado, Boulder We propose to detect or at least place strong upper limits on the abundance of C IV in 7 strong (280-740 mAngstrom\ equivalent width) low-redshift LyAlpha absorption systems along the line of sight to the bright quasar H1821+643. This quasar lies in an extensively surveyed field, so that all LyAlpha absorbers are known to be within 10^2-10^3 kpc of a neighboring luminous galaxy. We will be sensitive to C IV absorption at the 15-30 mAngstrom\ level, well below the average C IV equivalent width associated with low- redshift LyAlpha absorbers of this strength, as inferred by line-stacking techniques using FOS data. The C IV measurements will begin to map the extent of the metals associated with galaxies or with the large-scale environment in which they form. Measurements of higher Lyman series lines scheduled for FUSE or already available will constrain the H I column density and hence the metallicity. As a result, initial studies of the metallicity gradient of the intergalactic medium (IGM) at large distances from luminous galaxies will be possible. Such studies are possible only at the lowest redshifts, where we know the locations of the LyAlpha clouds from HST spectroscopy and the galaxies from ground-based redshift surveys. ================================================================================ Proposal Category: GO Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8183 Title: Morphology of the most massive galaxies in the early universe PI: George Miley PI Institution: Sterrewacht Leiden High redshift radio galaxies (HzRGs) are fundamentally important probes of galaxy and cluster formation. They are amongst the most massive galaxies in the early Universe and located in dense cluster environments. Our previous WFPC2 data have revealed that HzRGs are remarkably clumpy on a sub-kiloparsec scale, reminiscent of simulations of forming massive ellipticals. Surprisingly our NICMOS images often show clumpy aligned morphologies unlike those expected from an old elliptical population. There is a wide diversity in HST morphologies and colour distributions for the 9 objects for which we have both WFPC and NICMOS images. We propose to observe obtain WFPC2 images of 10 additional z ~ 2 radio galaxies for which we have NICMOS but no WFPC2 images. The new data will be used to (i) determine the range of clumps colour distributions, thereby constraining the formation history and the nature of the radio/optical alignment effect (ii) compare them with the colours of Lyman --break galaxies (iii) compare them with dust properties and the surmised axis of the jet orientation (iv) confirm relationships between clumpiness and other HzRG properties indicated by our present small sample. These observations will comprise part of a multiwavelength study of HzRGs, involving SCUBA on the JCMT as well as Keck and the VLT. ================================================================================ Proposal Category: GO Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8184 Title: The Origin of cD Envelopes PI: Patrick C\^ote PI Institution: California Institute of Technology Approximately 20\ Located at the dynamical centers of their host cluster or subcluster, these supergiant elliptical galaxies show extended, diffuse stellar envelopes which trace the gravitational potential of the surrounding cluster. A leading model for their formation involves the growth of cD envelopes through mergers and/or tidal stripping of other cluster galaxies. Unfortunately, the envelopes have extremely low surface brightness, making direct observational tests of this model using either spectroscopy or broadband colors virtually impossible. On the other hand, globular clusters (GCs) are ideal tracers of the underlying stellar populations of cD envelopes. Since the mean metallicity of GCs is known to depend strongly on the total luminosity of the galaxy in which they form, an inescapable implication of cD envelope formation through mergers or tidal stripping is that the total luminosity of the envelope progenitor galaxies must be imprinted in the metallicities of the GCs now associated with these galaxies. We propose to use the superb imaging capabilities of HST to measure colors, and hence metallicities, for several hundred GCs surrounding six nearby cD galaxies. Our short program will triple the number of cDs having accurate GC metallicity distributions, and will provide the first strong constraints on the luminosities of the progenitors of cD envelopes. ================================================================================ Proposal Category: GO Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8185 Title: Optical Nuclear Hotspot in NGC 1068 PI: Robert Antonucci PI Institution: University of California, Santa Barbara Early HST observations by Lynds Etal\ revealed a nuclear optical ``hotspot" with FWHM ~ 0.''25, now known to be displaced ~ 0.''1 from the most probable location of the `hidden' nucleus. The nature of the hotspot is mysterious and will be addressed by a high SNR STIS spectrum, combined with existing polarimetric observations. ================================================================================ Proposal Category: GO Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8186 Title: The Properties of Gaseous Halos Around Disk Galaxies PI: Joel Bregman PI Institution: University of Michigan Gaseous halos are key components in the structure and evolution of spiral galaxies and here we propose to advance our understanding of these phenomena through absorption line studies of the halo gas around the LMC and the edge-on galaxy NGC 891. In the LMC we will determine the spatial extent of the halo and the mass of highly ionized gas by measuring the CIV line strength against three bright background AGNs at different disk locations. For the edge-on system NGC 891, we will observe an AGN that we discovered whose sightline passes through the X-ray, radio, and HAlpha halos, only 5 kpc from the disk. By observing the Mg II and Fe II resonance absorption lines, we will measure the filling factor, density, and pressure of this halo material and determine the mass of gas that cools at this height above the disk. ================================================================================ Proposal Category: GO Scientific Category: DISTANT GALAXIES ID: 8187 Title: STIS Imaging of the Deep NICMOS Parallel Fields: Building on the NICMOS Legacy PI: Patrick McCarthy PI Institution: Observatories of the Carnegie Institution of Washington We propose to use the STIS/CCD to image 15 high latitude field imaged with NICMOS as part of the public parallel program. The STIS images will yield visual morphologies to magnitudes of 24.5 and quantitative measures of image structure to 26.5 or fainter in two orbits. These data will allow us to 1) derive the morphologies of a sample of HAlpha selected L^* galaxies at 0.7 < z < 1.9, 2) assess the impact of patchy extinction on the population of very red galaxies, and 3) compare the rest-frame visible and UV morphologies of a large number of galaxies over a wide range of luminosities and colors to understand the degree to which optical selection biases our view of galaxy evolution. This modest investment of observing time will complement the Hubble Deep fields and will greatly enhance the value of the NICMOS, STIS and WFPC2 archive of faint galaxy data. ================================================================================ Proposal Category: SNAP Scientific Category: STELLAR EJECTA ID: 8188 Title: Snapshot Spectroscopic Diagnostic Survey of the Symbiotic Stars PI: Charles D. Keyes PI Institution: Space Telescope Science Institute We propose to obtain G140L and G230L STIS spectra and nearly contemporaneous ground-based optical spectra of as many as possible of the known symbiotic stars for which no usable ultraviolet data exist. Currently, reliable fundamental parameters are available for only 10 percent of the approximately 150 known or suspected symbiotics. For the components of many individual systems, we will determine physical parameters such as Zanstra temperatures, emission line diagnostic electron temperatures and densities, and limits on red giant wind velocity laws and mass-loss rates. More importantly, we will be able to establish meaningful statistical limits on the nature of hot component sources of ionization and fundamental wind parameters, which are vital steps toward understanding the accretion hydrodynamics and the evolutionary status of symbiotic systems. ================================================================================ Proposal Category: GO Scientific Category: DISTANT GALAXIES ID: 8189 Title: The Source of Gamma Ray Bursts and the Nature of their Hosts PI: Andrew Fruchter PI Institution: Space Telescope Science Institute We propose to use the unique high-resolution optical and ultraviolet capabilities of HST to investigate the physics of gamma-ray bursts (GRBs) and the nature of their host galaxies. Our approach is three-pronged: 1) rapid ultraviolet spectroscopy obtained within days of several outbursts will allow us to probe the physics of the relativistic fireball and constrain the density of the surrounding medium and the dust extinction in the host to the fireball, and in many cases will provide the redshift of the GRB; 2) ultraviolet spectroscopy and imaging will allow us to obtain redshifts of host galaxies which cannot be found by Keck or the VLT (due to a lack of strong visible lines in the redshift range 1.3 < z < 2.4), permitting us to measure the rate of GRBs as a function of cosmological time; 3) optical images of the hosts taken both shortly after outburst and up to a year later will permit a study of the morphology of the hosts, determination of the position of the burst on the host to 100 pc accuracy, and examination of the late time behavior of the afterglow. The morphology and astrometry will provide a crucial discriminant between models for the creation of GRBs; the long-term behavior of the light- curve probes the density of the host ISM and the energetics of the fireball. This comprehensive set of observations will provide new insights into the astrophysics of GRBs and their high redshift host galaxies. ================================================================================ Proposal Category: GO Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8190 Title: The Nuclei of `Warm' Ultraluminous Infrared Galaxies -- Superstarbursts or AGN PI: David Sanders PI Institution: University of Hawaii We propose high resolution spectroscopy with STIS of four of the nearest `warm' ultraluminous infrared galaxies (ULIGs) that were discovered in the IRAS database, and for which we have recently obtained WFPC2 images in B,I filters. These objects are thought to represent a critical evolutionary link between ULIGs and optically selected QSOs. Recent observations also suggest that these objects were much more numerous at high redshifts (z = 1-4), and that they may account for a substantial fraction of the far- infrared/submillimeter as well as X-Ray background.. Our Cycle 5 PC observations show that the nuclear regions (<1-2^ ) of all of these objects appear to contain a population of massive star clusters (M ~ 10^6-10^8\ M_\odot), plus one or two `super knots' that are either the most massive star clusters yet observed (M > 10^10\ M_\odot ================================================================================ Proposal Category: GO Scientific Category: DISTANT GALAXIES ID: 8191 Title: The Faintest Radio Galaxies: Interacting Starbursts at z<1 PI: James Lowenthal PI Institution: University of Massachusetts We propose deep WFPC2 imaging and STIS slitless spectroscopy of two of our ultra-deep VLA fields. Those 4- and 6-cm maps have 1-Sigma levels of 3 and 11 Mu-Jy, respectively, comparable to VLA observations of the HDF, and show 14 and 9 sources in statistically complete samples. Keck spectroscopy and imaging to B, R, I ~26.5 have identified most of the sources as compact, luminous starbursting and interacting galaxies at redshifts z es1; about 25\ at z>1.5. Our goals here are: (1) identify the remaining sources; (2) pinpoint regions of star formation; (3) quantify the incidence of interaction using spatially-resolved kinematics; (4) quantify morphologies; and (5) constrain the evolution of these faintest of radio sources. Only the HDF and one other field have such deep VLA, HST, and Keck data, and there is strong evidence that field-to-field variations are significant. WFPC2 images with F814 will provide the resolution needed to measure morphologies on sub-kpc scales, identify interaction-induced star-formation, and distinguish AGN from non-AGN components. Slitless spectroscopy with STIS will reveal faint emission-line sources invisible in our Keck images and will provide spatially- resolved kinematics, necessary to disentangle the starforming components in interacting systems. The VLA fields extend over some 8\min\ each, so both WFPC2 and STIS can be used simultaneously. ================================================================================ Proposal Category: SNAP Scientific Category: FIELD STELLAR POPULATIONS ID: 8192 Title: A Snapshot Survey of Probable Nearby Galaxies PI: Patrick Seitzer PI Institution: University of Michigan The census of galaxies in the Local Volume of space is very incomplete, particularly at the faint end. We propose a snapshot survey to use the high spatial resolution of HST to determine whether selected galaxies are nearby on the basis of resolution into stars, and the magnitudes and colors of the brightest stars. Our sample is chosen from the survey by team members Karachentsev & Karachentseva (KK98) of some 260 nearby dwarf galaxy candidates. Our F555W & F814W snapshot survey will concentrate on the 75 candidates most likely to be within 4 Mpc. One HST orbit per galaxy results in a distance from the magnitude of the tip of the red giant branch (TRGB) and is sufficiently deep to identify the brightest stellar population. Keck, VLT, and other large telescopes will be used for spectroscopic follow-up for abundances and kinematics. As an example of the science to follow from this survey, consider the incompleteness of the dwarf galaxy census of the Local Group. Comparisons with the composite luminosity function of nearby groups indicate that there may be as many as ~ 30 faint Local Group members yet to be discovered. If only 10\ to be Local Group members, the luminosity function of the Local Group will no longer appear truncated. ================================================================================ Proposal Category: GO Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8193 Title: Comparing the Hosts of High-z Radio-Quiet Quasars to Lyman Break Galaxies PI: Timothy M. Heckman PI Institution: The Johns Hopkins University The underlying causes of the rapid cosmological evolution of the quasar population are a mystery around which are woven many different strands of contemporary cosmology. Progress on this problem would have important implications for understanding the early heating of the IGM, the formation and early evolution of galaxies, and of course the quasar phenomenon itself. We have begun a program with HST to image the host galaxies of a carefully- selected sample of five high-z (z ~ 2 to 3) radio-quiet quasars in order to compare the photometric and structural properties of the host galaxies to those of the field population of normal star-forming galaxies at similar redshifts (the `Lyman break' galaxies). We have already obtained deep H-band NICMOS (rest-frame visible) images of this sample, and find that the host galaxies are similar to the Lyman break galaxies in terms of their compact sizes and moderate luminosities. In the present proposal we request time to obtain WFPC2 images in order to extend this comparison into the crucial rest- UV spectral window, where the young stellar population can be most directly probed. This information is essential to begin to understand the long- hypothesized relationship between quasars and galaxy-building in the early universe. We emphasize that if the quasar host galaxies have UV sizes and luminosities similar to typical Lyman break galaxies, we will be able to detect them. ================================================================================ Proposal Category: GO Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8194 Title: Evolution of high-redshift Seyfert Galaxies PI: Guenther Hasinger PI Institution: Astrophysikalisches Institut Potsdam The ROSAT Deep Survey covers an area of 0.3 deg^2 in the direction of the Lockman Hole and has found a source density of ~ 1000 deg^-2 with fluxes above 10^-15 cgs. Spectroscopic identifications of optical counterparts at the Keck telescope are complete to an X-ray flux limit of 2 \cdot 10^-15 cgs and optical magnitudes of R<23.5^m. Approximately 70\ 0.08 to 4.45. This is the highest AGN surface density detected in any waveband. The X-ray luminosity function of AGN shows substantial density evolution, resulting in a significantly larger space density of low-luminosity AGN (mainly Seyferts) in the redshift range 1 < z <2, than expected from the conventional pure luminosity evolution models. We have selected a statistically complete sample of Seyfert galaxies from the ROSAT Deep Survey. The galaxies have a redshift range of 0.9--1.9; this is the most distant available Seyfert sample. We propose to image these objects with broad-band WFPC2 filters in order to investigate the evolution of their morphology and environments. The observations will provide insights into the Seyfert phenomenon at intermediate redshift and will complement similar HST studies of normal galaxies, clusters and quasars. ================================================================================ Proposal Category: GO Scientific Category: FIELD STELLAR POPULATIONS ID: 8195 Title: The Stellar Halo and the Metallicity Distribution Function in the Giant Elliptical NGC 5128 PI: Gretchen Harris PI Institution: University of Waterloo We propose to measure the metallicity distribution function (MDF) of the halo stars in the nearby (d ~ 3.9Mpc) giant elliptical galaxy NGC 5128 by direct (V,I) color-magnitude photometry of its old red-giant stars. Because NGC 5128 is 2 magnitudes closer than any other giant E galaxy, it gives us a unique opportunity to study the enrichment history at a level of detail that is impossible for any other such galaxy. In a previous highly successful Cycle 5 program, we obtained a deep color-magnitude study of the halo in a field projected ~eq 21 kpc from the center of NGC 5128, which shows that the MDF is extremely broad but dominated by an old and metal-rich (Fe/H ~eq -0.6 up to 0.0) stellar population. In Cycle 8, we propose to measure two more fields: a very remote one at 40 kpc, and a second one in the inner halo at 7 kpc. At the distance of NGC 5128, the photometric limits of the WFPC2 camera reach almost 3 magnitudes in I down the red giant branch, allowing the construction of an accurate MDF. All our target fields are located well away from the dust lanes and thus not affected by internal reddening or the presence of young stars. Combined with our Cycle 5 data, these three halo fields will allow us to study the MDF and metallicity gradient through the halo, and connect these to enrichment history models. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8196 Title: High Spatial Resolution UV/Optical Spectroscopy of H II Regions in the Magellanic Clouds PI: Donald Garnett PI Institution: University of Arizona We propose to obtain high signal/noise UV/optical spectra of several H II regions in the SMC and LMC with STIS to make definitive measurements of the abundances of C and N in the Clouds, and to study the temperature, density, and ionization structures of the nebulae at 10^17 cm resolution. We will measure gas-phase C/O and N/O ratios from UV emission lines of C III, N III, and O III, which can provide very reliable abundance determinations. The new C/O and N/O measurements will be used to address apparent discrepancies between C and N abundances in the H II regions and those derived in luminous stars in the Clouds. N III measurements will provide the first reliable N abundances in the Clouds, and resolve disagreements between optical and IR abundance determinations. We will look at the magnitude of spatial variations in C/O and N/O to study the efficiency of mixing of PN ejecta in the ISM. Measurements of Si III Lambda1883 will yield accurate Si/O ratios and a better understanding of grain depletions in a variety of environments. Our H II region sample overlaps that of an ISO IR spectroscopy program, which will provide complementary information on several ions not observable in the optical/UV spectrum. High spatial resolution mapping of physical conditions and ionization will enable us to develop photoionization models of greatly improved accuracy for the Magellanic Cloud regions. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8197 Title: Detection of ^11B/^10B: Part II PI: Douglas Duncan PI Institution: University of Chicago HST observations (e.g. Duncan Etal 1992; 1997) have led to new theories of how cosmic rays (CRs) rich in CNO near massive stars form the light elements Li, Be, and B (e.g. Ramaty Etal 1996, 1998). The neutrino process in SN, which has never been experimentally verified, should also produce boron, but only ^11B, yielding a very different isotopic ratio than CR spallation. The boron isotope ratio, \bele/\bten, can provide a definitive test of both these theories, but its galactic evolution is completely unknown. Our previous GHRS echelle observation of the moderately metal-poor (Fe/H=-1.0) star HD76932 placed a limit on its B isotope ratio, but not a definite value, because possible blending from an unknown spectrum line could not be ruled out (Rebull Etal 1998). The discovery of a halo star greatly depleted in B (Primas Etal 1998b) provides a wonderful opportunity to make the result definite. By comparing two similar (Fe/H ~ -1.6) stars, which have very different amounts of B, we can rule out or measure any blends. This should give a definite result for \bele/\bten\ at metallcity Fe/H ~ -1.6, an epoch when massive star SN should have dominated galactic nucleosynthesis. Furthermore, we can then use our blending knowledge to reanalyze HD76932, getting a definite result for its \bele/\bten\ ratio as well. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8198 Title: Understanding the Starburst-like Dust in the Small Magellanic Cloud PI: Karl Gordon PI Institution: Louisiana State University The similarities between the ultraviolet extinction found in the star forming bar of the Small Magellanic Cloud (SMC) and starburst galaxies has highlighted the importance of understanding the dust extinction in the SMC. The behavior of the UV extinction in the SMC is unlike that seen in any other Local Group galaxy. In a recent study, it was shown that the traditional (no 2175 Angstrom\ bump, high far-UV rise) SMC extinction curve is seen in the SMC's star forming bar, while outside of this bar a much more Galactic (2175 Angstrom\ bump, weaker far-UV rise) extinction curve is seen. These results are tentative due to the fact that only four extinction curves are known with certainty in the entire SMC. We propose to determine the ultraviolet extinction curves toward three additional stars stars in the SMC. These sightlines were chosen to be located near differing levels of star formation activity. In addition to helping understand the origin of the UV dust extinction in starburst galaxies, study of the spatial variation of UV extinction in the SMC also holds the promise of helping to understand the origin of the 2175 Angstrom\ bump. Understanding the behavior of dust in starburst regions is important as the differences between the extinction corrections for the Milky Way and the SMC is a factor of 10 at 1500 Angstrom. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8199 Title: Local Cosmology: The Nearby Flow Field and its Structure PI: Marc Davis PI Institution: University of California It is a curious fact that very little data are available to constrain the velocity field of galaxies in the local neighborhood (<= 500 km/sec). Although tremendous progress has been made in recent years in mapping the large-scale gravitational field (out to scales of cz ~ 10,000 km/sec), the major impediment to constraining the local flow is the lack of a consistent set of distances to nearby galaxies. Locally the deviations from a pure Hubble flow have been predicted to be large and measurable, as much as 1 magnitude( ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8200 Title: Globular Cluster Systems in Three Giant Coma Ellipticals PI: William Harris PI Institution: McMaster University In our previous imaging programs in Cycles 4 and 5, we have investigated the luminosity functions, metallicities, and specific frequencies of the globular cluster systems in three Coma giant ellipticals: the central cD NGC 4874, and two normal giants NGC 4881 and IC 4051. These three have turned out to be surprisingly and sharply different in globular cluster specific frequency, metallicity distribution, and spatial structure. In certain cases, they display a unique combination of factors which we have seen in no other galaxies (such as extremely high specific frequency in a normal and non- central cluster elliptical; distinctly unimodal metallicity distributions; or enormously large core radius). These Coma ellipticals present serious challenges to virtually every one of the current formation scenarios for globular cluster systems. Coma is the densest and richest cluster of galaxies in which globular cluster populations lie within reach of the HST cameras. We propose to investigate this rich proving ground further by deep V,I WFPC2 imaging of three more of its giant ellipticals: the central (non-cD) supergiant NGC 4889, the outlying cD NGC 4839, and another normal luminous gE in the core region, NGC 4926. These targets will considerably extend the range of parameter space that we have sampled in the systematics of globular cluster populations. ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8201 Title: The Ultraviolet Properties of Ultra-Luminous Infrared Galaxies PI: Gerhardt R. Meurer PI Institution: The Johns Hopkins University Ultraluminous Infrared Galaxies (ULIRGs) are the most luminous galaxies known in the local universe, and are predominantly powered by massive star formation. ULIRGs are the only type of star forming galaxies in the local universe with bolometric luminosities approaching those of the Lyman-dropout systems and SCUBA sub-mm detections at z~ 3. However, very few observations of ULIRGs exist at ultraviolet (UV) wavelengths to compare to these high-z detections. Here we propose imaging a modest size sample of ULIRGs in the UV with STIS. This will extend the observations of these objects into the wavelength range where massive stars dominate the intrinsic spectrum. We will then be better able to compare the rest-frame UV morphology and overall SEDs of ULIRGs to the high-z systems. We will test whether transmitted UV light traces star formation and whether the UV SED reddens with dust absorption as is the case for UV selected starbursts. We will assess what impact ULIRGs make on rest-frame UV surveys of galaxies. Our images combined with archival optical to near IR images will build on the HST heritage allowing key issues concerning the physics of ULIRGs to be addressed. These include the relative importance of clustered versus diffuse star formation, the mechanism of star formation feedback, and whether and how UV light escapes these dusty systems. ================================================================================ Proposal Category: SNAP Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8202 Title: Bright Quasar Close Lensing Search PI: Michael Gregg PI Institution: University of California, Davis We propose a second generation snapshot survey of bright quasars, optimized to find lenses with component image separations < 1". Most models of the lens components predict distributions which peak at separations in the range 0arcs5 to 1", yet the observed distribution of lenses peaks at 1arcs3. The lack of observed systems with close separations is difficult to reconcile with a geometrically flat universe, preferred by theory (inflation) and the observational determinations of the cosmological constant from type Ia supernovae. The survey will improve over the earlier pre-refurbishment snapshot survey of quasars (Bahcall et al.\ 1992; Maoz et al.\ 1993) in two important respects. With the restored PSF, new images will be considerably more sensitive to the presence of both close separation and faint lens components, and because STIS reaches 2 magnitudes fainter than the PC, the snapshot images can be kept to short exposures, containing the typical trailing under gyroscopic guiding to less than a pixel (<0arcs05). ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8203 Title: Dwarf busting in Abell 868 PI: Simon Driver PI Institution: University of St Andrews We request 24 orbits to obtain a deep mosaic (6 * 4-orbit pointings) of the central region of A868, a rich Abell cluster which we have imaged comprehensively from the ground. The objective is to identify and characterise the morphological nature of the dwarf galaxy population(s) responsible for the steep upturn seen in this cluster's luminosity function. While similar upturns have been reported in many clusters, the specifics of the dwarf population remain unknown as these objects cannot be resolved from the ground. What type of dwarf galaxies are they ? Is there more than one population contributing ? How are they clustered ? By obtaining deep high-resolution HST WFPC2 imaging over a central strip of 7.5' * 3.75' we will be able to measure morphologies, light-profiles and the clustering properties of the dwarf population(s) down to M_I = -16 mags (H_o=75kms^-1Mpc^-1). Although we shall primarily concentrate on the dwarf galaxies, we will also recover the cluster's morphological luminosity distributions for elliptical, spirals and irregulars over a broad absolute magnitude range (-24 < M_I < -16 mags) as well as the more quantitative bivariate brightness distribution (-24 < M_I < - 16 mags, 17.0 < mu_e^I < 25 mags per sq arcsec). Comparing these results to those recently derived for the general field will provide an insight into the environmental influences on morphology and surface brightness. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8204 Title: Calibration of the Wind Momentum--Luminosity Relationship in Cyg OB2 PI: Artemio Herrero PI Institution: Instituto de Astrof'\isica de Canarias We propose to improve the calibration of the Wind momentum -- Luminosity Relationship of hot stars at solar metallicity by adding new objects with well determined distances, stellar parameters and wind momenta. We propose to acquire STIS low-resolution FUV spectra of O- and B-supergiants belonging to the same OB association to determine their terminal wind velocities. We selected stars in Cyg OB2, for which we alredy have optical observations and have performed analyses (or which are currently under way) with our model atmospheres codes to determine their stellar parameters and mass loss rates. A precise calibration of the WLR using objects of the solar neighbourhood is crucial for future applications of the method to determine extragalactic distances out the Virgo and Fornax clusters of galaxies. ================================================================================ Proposal Category: GO Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8205 Title: UV Spectroscopy of Infalling Cometary Material in Solar- Type Pre-Main Sequence Stars PI: Carol Grady PI Institution: National Optical Astronomy Observatories, STIS Group Models for the formation of the Solar System predict that an intermediate stage in planet formation was the assembly of material in the disk into planetesimals, and that this should be a common step in the evolution of planetary systems. Planetesimals are difficult to detect directly except by activity in renewing the small grain population in mature (e.g. t>100 Myr) planetary disks, or by the presence of cometary activity. Cometary activity can provide a marker for the presence of planetesimals in younger systems where much of the dust is a remnant of the original protoplanetary disk. The presence of such cometary activity has been inferred from redshifted absorption features in the optical & UV spectra of Beta Pic and a large number of younger, intermediate-mass pre-Main Sequence stars. However, if the interpretation of these features as the aggregate comae of swarms of star- grazing bodies is correct, similar activity must be present and remotely detectable in the disks of young, solar analogs. We propose using HST STIS to obtain the first UV spectroscopic observations of infall activity in the disks of young, Solar-type stars, supplemented by a comparison intermediate- mass star. The data will be used to determine whether infall activity around young Suns evolves on the same time scale as for disks around more massive and luminous stars. ================================================================================ Proposal Category: GO Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8206 Title: The Structure of the Accretion Flow on pre-main-sequence stars PI: Erik Gullbring PI Institution: Stockholm Observatory We propose to test an essential prediction of the magnetospheric accretion model for T Tauri stars. STIS echelle spectra will be used to search for the relatively narrow high-temperature emission lines that must result from the magnetospheric accretion shock, but are not expected in the previous, alternative boundary layer model. By combining the results from high temperature (10^5 K) lines, accessible only with HST, with optical lines and optical-UV continuum emission, we will develop physically self-consistent models of accretion shock structure. The geometrically distribution of the emitting gas as derived from our results will test theories of mass-loading of magnetic field lines at the magnetosphere-disk interface. Analysis of the UV emission lines will also provide improved calibrations between ultraviolet continuum emission and accretion luminosities, and thus improve estimates of mass accretion rates for T Tauri stars. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8207 Title: The Ofpe/WN stars in M33: understanding Wolf-Rayet star formation in different environments PI: Luciana Bianchi PI Institution: The Johns Hopkins University We propose to obtain STIS Ultraviolet spectra of seven Ofpe/WN9 stars (``slash stars'') in M 33 discovered from ground-based (KPNO, MMT) classification spectra of the 400 UV-brightest stellar sources measured in the Ultraviolet Imaging Telescope images (Massey, Bianchi, Hutchings & Stecher 1996). The purpose is to derive stellar parameters (T_eff, Luminosity, Radius, Mass, element abundances, mass-loss rate, and wind velocity) by modeling wind and photospheric line profiles. The measured stellar quantities will be compared (a) with our previous HST observations of O supergiants and WNL stars in M33, and (b) with archive spectra of Ofpe/WN9 stars in the Galaxy and the LMC. The program will provide constraints on the evolutionary scenarios for Ofpe/WN9 interpretations, clarify on the formation of Wolf-Rayet stars, and will extend our comparison of massive populations in Local Group galaxies to another, important class of objects. WFPC2 imaging parallel to the primary spectroscopy in UBV and FUV filters will allow to substantially extend our study of the hot massive star population and populous stellar clusters in this galaxy. ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8208 Title: Galaxy Interactions, Tidal Debris, and the Origin of Intracluster Light in the Coma Cluster PI: Michael Gregg PI Institution: University of California, Davis We propose to obtain deep WFPC2 and parallel STIS images of three extended, low surface brightness objects that we have recently discovered in the Coma cluster; these objects are tidal debris being stripped from galaxies and added to the general cluster background. These images will enable direct study of the brightest blue and red supergiants, globular clusters, and star forming regions which may be present, or will place strong limits on the numbers of such objects and any recent star formation. We also propose similar observations of two spirals in the core of Coma: both are losing their ISM to the hot cluster gas and one is the source of one of the low surface brightness tidal features. By imaging these galaxies, we will get a high resolution look at the interaction between the cluster and interstellar media, as well as any ram-pressure induced star formation. The tidal features in Coma appear to be adding material to the background light and cD galaxy envelopes at a significant rate; determining the nature of the added stellar population and the interactions which produce it are critical to understanding the formation and evolution of cD galaxies and clusters. ================================================================================ Proposal Category: GO Scientific Category: BINARY STARS ID: 8209 Title: The Complex Circumstellar Environment of the Massive Contact Binary RY Scuti PI: Robert D. Gehrz PI Institution: University of Minnesota RY Scuti is a very massive and luminous evolved contact binary system. The combined luminosity of the stellar components is near the Eddington limit, resulting in complex, time variable mass-loss and mass-transfer in the system's common envelope. It is surrounded by an unusual nebula that is only a few arcseconds in extent. Our previous ground-based infrared observations have shown a compact dust torus in the equatorial plane of the system. Our recent HST/WFPC2 images have revealed a set of ionized rings at the inner edge of this dust torus, as well as several other complex structures within 1" of the star. We propose to obtain STIS spectra that will spatially resolve the spectrum of the star from its compact nebula for the first time. This will allow us to investigate the complex mass loss winds responsible for the formation of the nebula. We also propose to duplicate our successful HAlpha images in order to investigate possible variability of the nebula resulting from eclipses in the binary system. Finally, we propose to image RY Scuti in SIII, which will probe the excitation conditions in the nebula when compared with our HAlpha image. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8210 Title: HST Imaging of Bipolar Proto-Planetary Nebulae and Circumstellar Arcs PI: Bruce Hrivnak PI Institution: Valparaiso University Proto-planetary nebulae (PPN) provide the best opportunity to test theories of asymptotic giant branch mass loss (symmetric/asymmetric, continuous/episodic) and the processes which shape planetary nebulae. These remain among the outstanding unsolved problems in stellar evolution. We propose to use WFPC2 to observe several new PPN which display evidence of being bipolar, to study this phenomena. These will be modeled using our newly-developed axially-symmetric, 2-D, dust, radiation-transfer code. We have previously used WFPC2 to image 4 new bipolar PPN, and have successfully modeled their structures and spectral energy distributions. This proposal will extend this study to additional PPN and give important evidence on how common is the bipolar structure. In addition, we have found concentric arcs, seen previously in the Egg Nebula, to exist in 2 additional bipolar PPN. This has important implications for the mass loss mechanism. We will investigate the existance of these arcs in additional bipolar PPN by obtaining deep images. ================================================================================ Proposal Category: GO Scientific Category: BINARY STARS ID: 8211 Title: An Ultraviolet Census of Counterparts to Highly Luminous X-ray Sources in M31 Globular Clusters PI: Bruce Margon PI Institution: University of Washington The cores of certain globular clusters in our Galaxy contain some of the most extraordinary stars known, identified by their intense, near-Eddington limited X-ray emission. Essentially all are X-ray bursters, emitting L_x>10^4 L_\odot in a few seconds. At least one, and probably two, of these sources are the shortest binary period stars known anywhere: NGC 6624 contains a double- degenerate binary with an 11 minute orbital period. HST has enabled the optical identification and study of counterparts to a half-dozen of these sources in the Milky Way, but the systems prove to have a wide range of optical luminosities and orbital periods, with few obvious patterns emerging. However, one common characteristic of these sources is intense flux at 1400 Angstrom, a wavelength where the 10^5 cluster stars virtually disappear. The Andromeda Nebula is known to contain dozens of bright globular cluster X-ray sources. We propose here a modest, first imaging reconnaissance of globular cluster X-ray source counterparts in M 31 at 1400 Angstrom, with a goal of materially increasing the number of X-ray clusters with counterparts, and further exploring an odd dispersion of L_X/L_1400 seen in galactic clusters. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8212 Title: Reconciling the SBF and SNIa Distance Scales PI: Edward A. Ajhar PI Institution: National Optical Astronomy Observatories We propose to use WFPC2 to measure surface brightness fluctuation (SBF) distances to host galaxies of well-measured type Ia supernovae (SNIa) in order to resolve the discrepancy between H_0 values determined from the SBF distances and from SNIa distances. Currently, SBF distances yield H_0 ~ 80kmsMpc, and SNIa distances yield H_0 ~ 60. While both of these distance estimators provide excellent internal error consistency (near 5\ systematic errors are preventing these methods from providing consistent values for the Hubble parameter. Given that there are so few reliable methods for determining distances over large ranges, it is imperative that we understand the discrepancy between the SBF and SNIa methods. Only then can these methods converge on the true value of H_0. ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8213 Title: Globular Clusters of Low Surface Brightness Galaxies PI: Bryan Miller PI Institution: Leiden Observatory We propose to investigate globular cluster (GC) systems in giant low surface brightness (LSB) galaxies. The primary goals of the project are to determine the number of GCs in two nearby LSB galaxies and to estimate their ages. LSB spirals tend to be more isolated, more gas rich, and have had more quiescent star formation than their high surface brightness (HSB) cousins. LSB galaxies have either been forming stars very slowly for a Hubble time or have formed within the last few Gyr. Thus, their star formation histories may be very different from those of HSB galaxies. We will use the ages of the GCs to estimate the cluster formation histories of LSBs. The colors and magnitudes of their GCs will allow us to date the clusters and put constraints on when the galaxies started to form. Thus, we may be able to distinguish whether they are very slowly evolving or very young. We will also compare the specific globular cluster frequency (number per unit luminosity) and the shape of the GC luminosity function in LSBs with those quantities for GCs in HSB spirals. The results of this project will have important implications for galaxy and GC formation. ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8214 Title: The Evolution of Globular Cluster Systems In Early Type Galaxies PI: Carl Grillmair PI Institution: SIRTF Science Center We will measure structural parameters (core radii and concentrations) of globular clusters in four early-type galaxies using deep, four-point dithered observations. We have chosen globular cluster systems which have young, intermediate age, and old cluster populations, as indicated by cluster colors and luminosities. Our primary goal is to test the hypothesis that globular cluster luminosity functions evolve towards a ``universal'' form. Previous observations have shown that young cluster systems have exponential luminosity functions rather than the characteristic log-normal luminosity function of old cluster systems. We will test to see whether these young systems exhibit a wider range of structural parameters than old systems, and whether and at what rate plausible disruption mechanisms will cause the luminosity functions to evolve towards a log-normal form. A simple observational comparison of structural parameters between different age cluster populations and between different sub-populations within the same galaxy will also provide clues concerning both the formation and destruction mechanisms of star clusters, the distinction between open and globular clusters, and the advisability of using globular cluster luminosity functions as distance indicators. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8215 Title: New clues to the ejection process in young stars:, Forbidden line imaging of T Tauri micro-jets PI: Catherine Dougados PI Institution: Laboratoire d'Astrophysique, Observatoire de Grenoble Bipolar outflows play a fundamental role in star formation. However, the ejection and collimation mechanisms are still not identified. Classical T Tauri stars (CTTS) offer a unique opportunity to progress on this problem, as their optical forbidden line emission allows to trace collimated winds very close to the central star (d <= 100 AU). Determining the exact flow geometry and the line excitation mechanism is essential to obtain new clues to the mass -loss process in young stars. Our team has recently obtained at CFHT the first sub-arcsecond resolution (FWHM=0.15") images of micro-jets around 3 T Tauri stars: DISTANT GALAXIES Tau, CW Tau, RW Aur. They reveal unprecedented details about the morphology of these jets, strongly suggesting ejection and velocity variability. However, such ground-based studies are limited to high-accretion sources. We propose here to use the unique HST resolution capabilities to image for the first time the innermost regions of jets associated with 4 CTTs with R band magnitudes > 13. Extending our sample to less extreme stars is crucial if we want to derive meaningful constraints on the mass-loss process in CTTS. Images in the 3 narrow-band filters S ii, H_Alpha or N ii and O i and in the adjacent continuum will be obtained. We will thus have access both to the jet excitation conditions and intrinsic morphology, and compare them with theoretical predictions from MHD models. ================================================================================ Proposal Category: SNAP Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8216 Title: T Tauri Star Snapshot Survey II. Completing the CTTs Sample PI: Karl Stapelfeldt PI Institution: Jet Propulsion Laboratory Infrared and millimeter continuum photometry suggests that as many as 50\ solar nebula from which our planetary system formed. However, high resolution, high dynamic range optical images currently exist for only a few dozen of the hundreds of nearby T Tauri stars that may harbor observable disks. Initial HST imaging with WFPC2 has shown that circumstellar disks are detectable as reflection nebulosities adjacent to the bright PSF of the central star. We propose a continuation of our R-band SNAPshot survey of T Tauri stars in the five nearest star-forming clouds. The expanded source list includes all nearby classical T Tauri stars with HAlpha equivalent widths greater than 30 Angstrom\ - a group of objects which theory suggests are actively accreting material from circumstellar disks. Our goals are to determine the frequency of disk detections, to measure the disk sizes and constrain their masses, to identify the nearly edge-on systems which are particularly favorable for studies of disk geometry, and to discover new disks undetectable using other techniques. In combination with our Cycle 7 program, the result will be a large, uniform image database on as many as 140 young stars likely to possess circumstellar disks. This database will be of fundamental importance to understanding the nature of planet-forming environments and their frequency in the galaxy. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8217 Title: Tests of Stellar Models Using Four Extremely Massive Spectroscopic Binaries in the R136 Cluster PI: Philip Massey PI Institution: National Optical Astronomy Observatories We are proposing to observe four non-interacting double-lined spectroscopic binaries discovered in the R136 cluster by our Cycle 6 FOS spectroscopy (Massey & Hunter 1998, ApJ, 493, 180). These binaries are all of very early type (O3-4 + O3-8) and should prove to be of very high mass. These data will allow us to extend the empirical mass-luminosity relation to higher masses, providing crucial checks on stellar interior and atmosphere models. Examination of the WFPC2 archives reveals that at least three of the four systems undergo eclipses. We plan to obtain simultaneous spectroscopy and photometry for all four systems during a single 2-orbit visit. Fourteen such visits, over an interval of a few weeks, should provide direct measurements for the masses of eight of the highest mass stars ever analyzed. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8218 Title: Exploring Triton in the Act of Global Change PI: Alan Stern PI Institution: Southwest Research Institute Triton appears to be undergoing the start of a long-awaited, and perhaps fundamental, global seasonal change. As a result of this change, seasonally deposited ices should sublime into the atmosphere, revealing extensive areas of the more permanent underlying surface, most likely with different photometric properties. We propose a 6-orbit Cycle 8 program consisting of STIS mid-UV spectroscopy and VIS/mid-UV imaging in order to better quantify the changes now underway, and to provide a critical benchmark for Triton's photometric state before still more time elapses. HST is required for this work owing to Triton's small (0.13") apparent diameter and the need for UV observations. ================================================================================ Proposal Category: GO Scientific Category: BINARY STARS ID: 8219 Title: A Definitive Census of the Cataclysmic Variable Population in 47 Tuc PI: Christian Knigge PI Institution: Space Telescope Science Institute We propose to carry out a deep, far-ultraviolet (FUV), time-resolved, spectroscopic search for faint cataclysmic variables (CVs) in the globular cluster (GC) 47 Tuc. We will use STIS to carry out FUV slitless spectroscopy and imaging of this cluster at 6 epochs for a total of 30 HST orbits. Since crowding is not a problem in the FUV, this will yield time-resolved spectra and photometry of all UV-bright objects in the cluster core. Our CV census will be both deep enough to be essentially complete M_V(limit) ~eq 11 spectroscopically and ~eq 13 photometrically and ``broad'' enough to involve all of the following CV characteristics:, (1) UV brightness;, (2) blue FUV spectral shape;, (3) strong C iv 1550 Angstrom emission;, (4) He ii 1640 Angstrom emission (especially in magnetic systems);, (5) short time-scale (~ minutes) variability (flickering, WD spin);, (6) intermediate time-scale (~ hours) variability (orbital variations);, (7) long time-scale (~ weeks) variability (dwarf nova eruptions)., Tidal capture theory predicts that we should discover 40 CVs in 47 Tuc and spectroscopically confirm 25. These numbers are large enough to allow the first definitive test of the theory. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8220 Title: Galaxy M/L Ratios, the Morphology-Density Relation, and Weak Lensing in the z=1 Cluster of 3C184 PI: Marijn Franx PI Institution: Leiden Observatory We propose to obtain a deep mosaic of WFPC2 images for the radio selected cluster around 3C184 at z=0.996. This proposal is the last part of a program to take large HST WFPC2 mosaics of distant clusters. We augment the HST mosaics of the clusters with extensive ground-based spectroscopy and imaging from the Keck, MMT, ESO-VLT, NTT, and WHT telescopes. The large areal coverage in high-z clusters is essential for studying the whole cluster population, and for determining radial gradients in their properties. We have the following scientific goals: (i) Use the Fundamental Plane of early-type galaxies to measure the evolution of M/L ratios out to z=1, putting strong constraints on the (star) formation epoch of early-type galaxies. (ii) Determine the density- morphology relation at z=1, and its evolution from z=0 to z=1. The radial distributions of starburst and post-starburst galaxies, as well as galaxy mergers, will be of particular interest. (iii) Use weak lensing to derive the detailed mass distribution of the cluster. 3C184 is well suited because it is a massive, high redshift cluster, with a measured velocity dispersion. It will provide great leverage on galactic evolutionary studies because of its high redshift. The fully processed mosaic of this cluster, covering 5*5 arcmin (1.5times1.5h^-2 Mpc), will be made available to the astronomical community, with our other cluster mosaics at z=0.33, 0.58, and 0.83. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8221 Title: The next bright Galactic nova: High Resolution Imaging PI: Michael Shara PI Institution: Space Telescope Science Institute The recurrent nova T Pyxidis is one of only ~20 novae with known shells, and the only recurrent nova with clearly resolved circumstellar matter. A unique and once-in-a-generation opportunity will exist during T Pyxidis' next eruption (now overdue) to determine: 1) The uniformity and isotropy of material (both dust and different chemical elements) ejected in previous eruptions, and 2) The smallest structures formed in nova eruptions. We propose to use WFPC2 to image T Pyx after it erupts to search for fluorescence and reflection light echoes from, and small-scale structure in, the nova circumstellar gas and dust ejecta. Only two novae are presently known to have a highly structured shell that can be defined as ``very'' clumpy. These novae are GK Per (known from the ground) and T Pyx (HST cycle 4 WFPC2 images). It's unclear if this structure is common to all nova shells or, if it is, how the structure is created. Though T Pyx is ``overdue'' it may take several years before it goes off again. We therefore propose to use the TOO time, if allocated, to follow the eruption of the next bright Galactic nova with WFPC2 (if T Pyx does not erupt) to determine how quickly the ejecta of a nova become clumpy. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8222 Title: An Emission Line Survey of the Crab Nebula PI: Jeff Hester PI Institution: Arizona State University We propose to conduct a WFPC2 survey of the Crab Nebula in the light of emission from O I, S II, and O III, and in a single continuum band. WFPC2 observations have already dramatically reshaped our understanding of the Crab. They have shown that the filaments in the Crab are the result of Rayleigh- Taylor instabilities at the surface of the synchrotron nebula. These data also provide the first direct evidence of the existence of an extended remnant of freely expanding ejecta that surrounds the visible nebula and into which the synchrotron nebula is expanding. High spatial resolution observations of the range of conditions around the R-T unstable interface are needed if we are to develop this understanding further or apply it to questions of the overall structure and evolution of the remnant. We have also found that the subarcsecond structure of filaments strongly influences overall filament spectra. Detailed knowledge of the ionization structure of filaments at HST resolution is essential to interpret any spectroscopic observations of the Crab, and is needed in particular if we are to disentangle such structural effects from the spatial abundance distribution within the nebula. In addition to our specific scientific objectives, this survey will provide a data set that is essential to all future studies of the structure, dynamics, and evolution of the Crab. ================================================================================ Proposal Category: GO Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8223 Title: The nature of radio--optical alignments in faint radio sources PI: Mark Lacy PI Institution: University of Oxford Study of the host galaxies of high redshift AGN is important if we are to attempt to investigate the population of high redshift galaxies which are not selected on the basis of luminous starburst activity. However, it is first important to establish how much the AGN affects the observed properties of the host galaxies even in samples of relatively weak AGN. We propose to use objects from a flux-limited sample of 7C radio sources, one of the first complete samples of radio sources with a flux limit more than an order of magnitude fainter than 3C, to study the effects of weaker radio-loud AGN and their jets on the host galaxies of radio sources at z~ 1. This will complement studies already made or in progress of the much more radio-luminous 3C and 6C objects, and in particular we will be able to make a direct comparison with the 3C sample of Ridgway & Stockton (1997). Results from our ground-based study indicate that the alignment effect is still present in the 7C sample at z~ 0.7, but is probably weaker and on a smaller spatial scale than that in 3C. With HST data we can investigate the z~ 1 regime at high spatial resolution, and compare galaxies and quasars directly. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8224 Title: UV Imaging of Europa & Ganymede: Unveiling Satellite Aurora & Electrodynamical Interactions PI: Melissa McGrath PI Institution: Space Telescope Science Institute We propose to obtain ultraviolet images of Europa and Ganymede using STIS, with suitable filters to isolate atomic oxygen (1304 and 1356 Angstrom ) and hydrogen (Lyman-Alpha) emissions, to study the interaction of the Jovian magnetosphere with the tenuous oxygen atmospheres of these icy satellites. Previous spectroscopic observations, from both HST (with GHRS) and Galileo, suggest the presence of polar aurorae on Ganymede whose geometry would be clearly delineated in these images. Europa is expected to show an oxygen emission morphology similar to that recently discovered on Io. ================================================================================ Proposal Category: GO Scientific Category: AGN PHYSICS ID: 8225 Title: Absorption and obscuration in radio-loud quasars PI: Joanne Baker PI Institution: University of California, Berkeley The role of associated absorption systems and dust obscuration close to the central engines of AGN is not understood. Using the low-frequency selected Molonglo Quasar Sample, we have discovered evidence for direct links between obscuration/absorption and the radio properties of quasars that shed new light on the physics of radio source evolution. To establish these results unequivocally, we require near-UV spectroscopy with STIS on the HST of a complete set of 19 Molonglo quasars with 0.7~ 10^7 M_\odot will be confidently detected. Even for the most distant and most massive bulges we should either detect a black hole or derive a meaningful upper-bound. In combination with our acquisition images of the central ~5", our results will for the first time establish the black hole mass distribution and its relationship to bulge mass/luminosity and cusp-slope in a significant number of local spiral galaxies. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8229 Title: Spatially Resolved Spectroscopy of Titan's Atmosphere and Surface PI: Caitlin Ann Griffith PI Institution: Northern Arizona University Titan's atmosphere is likened to the Earth's atmosphere; it is nitrogen based, has a surface pressure of 1.5 bar, and has methane which plays the role that water plays on Earth. Because methane can exist in both gas and liquid phases, weather and methane clouds are hypothesized to exist on Titan. Yet Titan's greater column abundance of atmosphere and the cooler conditions may induce conditions more quiescent than found on Earth. Here we propose to investigate the clouds in Titan's atmosphere, first discovered this year (Griffith et al. 1998). Our goal is to study weather processes native to the Earth's lower atmosphere, yet in the exotic context offered by Titan. By scanning the 0.05'' STIS slit across of Titan's 0.8'' disk, we will build a 16x16 image of Titan. Each 0.05x0.05'' pixel will consist of a spectrum of resolution 500- 1200 (grating G750L). With methane's varying absorption coefficient acting as a vertical discriminator, we will resolve the opacity structure of the atmosphere over a range of altitudes from 400 km down to the surface. This combination of spectroscopy and imaging will allow us to detect clouds in Titan's atmosphere, determine their coverage, thickness and altitude range. We will also measure the surface reflectivity of Titan at 0.9 Mum, and map the distribution of haze in the northern and southern hemispheres at altitudes where the haze is formed. ================================================================================ Proposal Category: SNAP Scientific Category: DISTANT GALAXIES ID: 8230 Title: Snapshot Survey of Dynamically Close Galaxy Pairs from z=0.1 to z=0.5 PI: David Patton PI Institution: University of Victoria We propose to obtain snapshot images of a large, well defined, and dynamically selected sample of close galaxy pairs at moderate redshift. These pairs have been selected from the CNOC2 Field Galaxy Redshift Survey (0.110^5 -10^6 M(sun), the more prominent extraplanar dust complexes may be sites of star formation at high-\z, and there is evidence for H II\ regions associated with unresolved continuum sources far above the plane of NGC 891. We have established that such high-\z\ dust features and H II\ regions are not unique to NGC 891. We propose to image five edge-on spiral galaxies (D ~ 17 - 70 Mpc) with the \wfpc2. The proposed \bvi\ images will be used to identify sites of on-going star formation in the thick disks of these galaxies, all of which show evidence for high-\z\ dust complexes, and with ground-based H Alpha\ images will be used to study the stellar content of any such regions. The resolution and point-source sensitivity of the \wfpc2\ are crucial for studying these star-forming regions. We will also use these images to study interstellar matter in the thick disks of these galaxies with unprecedented detail and derive the fundamental properties of high-\z\ dusty clouds-- including sizes, extinctions, column densities, masses, and gravitational potential energies. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8243 Title: SINS: The Supernova INtensive Study - Cycle 8 PI: Robert Kirshner PI Institution: Harvard College Observatory Supernovae reveal the last stages of stellar evolution, create the chemical history of the Universe, energize the interstellar gas, and occupy the center of attention for the extragalactic distance scale and cosmology. HST can make unique contributions to understanding supernovae, as the SINS program has shown. Now HST is better than ever for this work: STIS is ideal for spatially -resolved observations of SN 1987A, where a rapidly developing encounter between the fast-moving debris and the stationary inner ring has just begun. Our approach for Cycle 8 is the intensive study of a few selected objects beyond SN 1987A: SN 1993J in M81, SN 1998bu, SN 1998S and a Target-of- Opportunity observation of a bright, new supernova to be discovered during Cycle 8. We aim to explore the UV emission from supernovae, exploit the spatial resolution of HST, and press the late-time observations of supernovae into uncharted territory. The SINS team provides extensive ground-based support and analytic power to create an effective observing program that uses HST to help understand the final, most violent stage of stellar evolution. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8244 Title: Probing Stellar Ejecta in SN 1006 through UV Absorption Spectroscopy PI: P. Frank Winkler PI Institution: Middlebury College The remnant of SN 1006 provides a unique opportunity to study ejecta from a Type Ia supernova through UV absorption spectroscopy. Absorption lines in the spectrum of the background Schweizer-Middleditch (SM) star have revealed the presence of cold Fe and Si with velocities up to 7000kms. These lines surely are due to ejecta, but extrapolation from a single line of sight to the entire remnant suggests a mass of Fe less than half the ~ 0.5\: Msun \ expected from a Type Ia supernova. A reliable inventory of the ejecta requires several such ``core samples'' through the remnant, but until now no other suitable background UV sources had been identified. A recent search has revealed four new background objects with which we propose to probe additional lines of sight through SN 1006: two quasars and two A0 stars. These are fortuituously well distributed about the 30'\ diameter shell---from only 2'\ away from the center (even closer than the SM star) to <=sssim 1'\ from the shell rim. In modest exposures with the STIS we can obtain low-resolution spectra in both the near- and far-UV which will lead to a much fuller picture of the ejecta distribution and address the following questions: (1) Are the ejecta in diffuse expanding shells, or fragmented? In stratified layers, or mixed? (2) Where is the reverse shock which reheats the ejecta located? (3) Can the ``missing'' Fe from the Type Ia supernova be accounted for? ================================================================================ Proposal Category: GO Scientific Category: BINARY STARS ID: 8245 Title: BLACK HOLE ACCRETION OUTBURSTS IN SOFT X-RAY TRANSIENTS PI: Carole Haswell PI Institution: University of Sussex UV observations of soft X-ray transients (SXTs) will be made using STIS. This is part of an extensive multiwavelength target of opportunity campaign to monitor newly discovered SXTs in outburst and throughout the subsequent decline. Recent work establishes that a high proportion of SXTs harbor black holes, so these observations provide an unrivalled opportunity to obtain high quality data from an accreting black hole. UV data is a keystone of our multiwavelength campaign because the disk regions of interest radiate predominantly in the UV. Emission lines will allow us to probe the kinematics of the inner disk region. We will examine the relative strengths of the reprocessed X-ray flux emitted in the UV, and the UV flux generated by viscous heating in the accretion flow. Multiwavelength observations will probe the physics of the accretion flow throughout the outburst. The observations will yield detailed quantitative tests of the models for SXT outbursts. The new STIS/MAMA capability to perform UV spectroscopy with 125 microsecond time resolution will be exploited. A proven HST/RXTE echo-mapping experiment will measure the size of the reprocessing regions in the accretion disk, and thus probe morphology changes as the decline proceeds. It is unknown what rapid UV variability we may find; recent RXTE discoveries suggest this may prove a rich source of information on the dynamics close to the event horizon. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8246 Title: The youngest massive star clusters in the SMC as clues to star formation in the early Universe PI: Mohammad Heydari-Malayeri PI Institution: Observatoire de Paris High resolution imaging with WFPC2 has recently allowed us to resolve two very tight clusters of newly born massive stars in the Small Magellanic Cloud (N81, N88A; STScI Press Release 25-98, 23 July 1998). These are the youngest massive stars accessible to direct observations at ultraviolet and optical wavelengths. Situated in an extremely rare category of \h2 regions in the Magellanic Clouds (only 5\frac to 10\frac across and of very high excitation), these stars should rank among the hottest ones in these galaxies. Although color-magnitude diagrams yield valuable information, follow-up STIS observations of so identified hot star candidates are imperative for obtaining spectral types and stellar parameters and establishing the H-R diagrams. Comparison with models will allow us to derive the evolutionary state of the stars and clarify the nature of the most intriguing ones. In particular, one of the stars is a Wolf-Rayet candidate, which is an extremely rare kind of massive star in the metal-poor SMC. If confirmed by the planned spectroscopy, this finding will be important for stellar evolutionary models. Since the SMC is the most metal-poor galaxy observable with very high angular resolution, the proposed observations will provide valuable templates for studying star formation in the very distant metal-poor galaxies which populate the early Universe. ================================================================================ Proposal Category: GO Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8247 Title: Hidden new-born massive stars in compact \h2 ``blobs'' of the Large Magellanic Cloud PI: Mohammad Heydari-Malayeri PI Institution: Observatoire de Paris High spatial resolution imaging with WFPC2 is necessary to resolve very tight clusters of massive stars at birth in the Large Magellanic Cloud. These are the youngest massive stars accessible to direct observations at ultraviolet and optical wavelengths. Situated in an extremely rare category of \h2 regions in the Magellanic Clouds (only 5'' to 10'' across and of very high excitation), these stars should rank among the hottest ones in these galaxies. Using medium-band continuum filters, we will place the resolved components on color-magnitude diagrams to identify the exciting stars. Continuum-free He, ii 4686Angstrom\ images will pinpoint the hottest components and the Wolf- Rayet candidates of the tight clusters. Imaging in HBeta, O, iii, and HAlpha will allow us to correct for the extinction and for the nebular emission. Following our recent HST result on the SMC ``blobs'' N81 (STScI Press Release 98-25, July 1998) and N88A, we are confident that the planned observations will uncover the stellar contents of the LMC objects N160A1, N83B-1, and N11A. These objects provide exceptional opportunities for studying various key phenomena related to massive star formation, in particular whether these massive stars form in isolation or inside co-spatial tight clusters. The observations will also enable us to study the ``blob'' phenomenon at different evolutionary stages in the chemically distinct evironments of the SMC and the LMC. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8248 Title: WFPC2 observations of potential JVAS/CLASS gravitational lenses PI: Peter Wilkinson PI Institution: NRAL University of Manchester The JVAS/CLASS gravitational lens surveys have been the most successful so far at finding new arcsecond-scale gravitational lenses. A total of 17 confirmed systems have been discovered. One surprising result is the number of doubly- imaged lensed systems compared to ``quad'' configurations. The doubles are under-represented in the current JVAS/CLASS lens sample by a factor 5 based on conventional models of the lensing galaxies. This may be partly due to an observational selection bias that favours the discovery of quad lens sytems over doubles. It is essential to ensure that no doubly-imaged lensed systems are missed. Previous WFPC2 observations of candidate lens systems have proved remarkably successful at confirming new lensed systems by the detection of lensed images and the lensing galaxies. Recent Cycle 7 NICMOS observations of JVAS/CLASS candidate systems discovered three new lens systems. However, several ambiguous candidates from the first two phases of the CLASS survey remain and two very strong new candidates from the recently observed final phase of CLASS have also been uncovered. Based on the observed lensing rate in JVAS/CLASS (1:500) we expect that the majority of these candidates will turn out to be lenses. There is a companion proposal to this one which aims to examine confirmed cases of gravitational lensing in the JVAS/CLASS surveys in more detail. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8249 Title: A Strong Lensing Survey of the Mass Distribution in X-ray Luminous Clusters PI: Jean-Paul Kneib PI Institution: Observatoire Midi-Pyrenees We propose to use WFPC2 for a gravitational lensing survey of the central regions of 16 X-ray luminous clusters from a statistically complete sample. Our sample is based on cluster detections in the ROSAT All-Sky Survey and is representative of the population of rich clusters at z~ 0.2. The proposed WFPC2 survey will, for the first time, provide an unbiased view of strong lensing (arcs, multiply imaged systems and arclets) by such systems. Specifically, the strong lensing features and the shear field in the central regions of these clusters will be used to reconstruct accurately the mass distribution from galaxy to cluster scales. The resulting mass maps will be compared with HRI and ASCA observations in order to probe the dynamical state of, and the prevalence of substructure in, the cluster core. In combination with other indicators of the clusters' evolutionary state (e.g. the presence of a stable cooling flow) our study will provide the first coherent picture of mass accretion onto clusters at an epoch where cluster growth through mergers is expected to be common. Furthermore, the accurate mass models resulting from this survey will allow us to probe fundamental properties of the distant galaxy population, as well as provide new natural lenses for observations at longer wavelengths. Finally, the proposed observations will allow us to investigate the morphological mix and evolution of the cluster galaxy population. ================================================================================ Proposal Category: GO Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8250 Title: Proper motions of bulge stars PI: Konrad Kuijken PI Institution: Kapteyn Institute We request second-epoch observations of two fields in the galactic bulge for proper motion measurements, using WFPC2. These observations will allow velocities to be measured with an accuracy of 70km/s, sufficient to study the rotation properties of the bulge and disk in these fields, the vertical kinematics as a function of stellar type, and the presence of kinematic substructure such as might be caused by accretion of small satellites or dissolution of globular clusters. Further, a proper motion selected color- magnitude diagram will yield the best possible depiction of the Galactic bulge turnoff point. The first epoch observations were two-band, single-dither exposures. For the second epoch we will only use one band, but use two half- pixel dithered positions to improve the position accuracy. ================================================================================ Proposal Category: SNAP Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8251 Title: The Second-Parameter Effect in Metal-Rich, Globular Clusters: A Snapshot Study of NGC 6441 PI: Horace Smith PI Institution: Michigan State University While it has long been known that at least one parameter besides the metallicity, Fe/H, determines the horizontal-branch (HB) morphology of Galactic globular clusters (GCs), our ignorance as to the nature of this second parameter (or parameters) has been a major stumbling block in understanding the formation history and age of the GC system. The newly- discovered hot HB populations in the metal-rich GCs NGC 6388 and NGC 6441 provide an unique opportunity for unraveling this second-parameter effect. Sweigart & Catelan (1998) have presented second-parameter models which predict unusually bright HBs for these GCs. We propose to test these models by obtaining B,V,I time-series photometry of the RR Lyrae variables in the core of NGC 6441 in order to determine whether, as predicted, the pulsation periods are unusually long as implied by a bright HB luminosity. If confirmed, this would argue against age or mass loss as the second parameter in NGC 6441 and, more generally, would have implications for the use of RR Lyrae stars as standard candles for determining GC distances and ages. A possible new class of bright RR Lyrae-like variables will also be investigated. The interplay between stellar evolution and cluster dynamics will be studied by comparing the radial distribution of the RR Lyrae stars to those of blue and red HB stars. We waive proprietary rights to any data obtained. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8252 Title: Extinction Curves of Distant Galaxies PI: Christopher Kochanek PI Institution: Harvard-Center for Astrophysics We propose to measure extinction curves in five external galaxies ranging in redshift from 0.039 to 0.96 using gravitational lenses that show differential extinction between the images. The program will more than double the number of galaxies in which extinction curves have been measured and it will provide the first such measurements far outside the local group, in early-type galaxies and at significantly different cosmic epochs. STIS spectroscopic observations will focus on the 2175Angstrom\ feature, combined with WFPC2 and STIS photometry to check for variability and extend the wavelength coverage. For the two systems in our sample that are radio quasars, we will be able to check for the presence of dust which is gray in the IR--UV spectral range. ================================================================================ Proposal Category: GO Scientific Category: AGN PHYSICS ID: 8253 Title: Jet Acceleration of Narrow Line Region Gas PI: Mark Whittle PI Institution: University of Virginia -13pt Recent progress in understanding the kinematics of the Narrow Line Region (NLR) in Seyfert galaxies has identified three distinct components --- a high velocity nuclear flow, a more widespread gravitational component, and a jet-accelerated component. In this proposal, we aim to isolate and study the jet-accelerated component. A ground based long-slit survey shows that the kinematic signature of jet interactions while detectable, is usually confused by the presence of the other two components. Higher spatial resolution is essential if we are to isolate the jet-perturbed gas. We have selected 11 Seyferts with linear (jet-like) radio structure, pre-existing HST emission line images, and some indication (kinematic and/or morphological) of a jet perturbed component. Using STIS, we will obtain one (or in some cases, two) long slit exposures of the OIII Lambda5007, taken along the radio axis and through the brighter emission features. This will allow us to zero in on the jet-accelerated gas --- isolating and measuring its strength, location, and velocity field, all of which can be used to test the nature of the jet-gas interaction. Our significant sample size also allows a `demographic' study of the interaction phenomenon. In the big picture, jet interactions are an important and widespread astrophysical phenomenon. Unlike other contexts, the pervasive distribution of line emitting gas in Seyfert nuclei provides the perfect `highlight' with which to study this interaction. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8254 Title: A Unique Calibration of Asteroseismology: the DBV GD358 PI: D.E. Winget PI Institution: Univeristy of Texas at Austin An improved understanding of the white dwarf stars has a great potential in both physics and astronomy. Determination of the basic physical parameters of the white dwarf stars will help us realize that potential; asteroseismology is the key. We can use asteroseismology to constrain the stellar structure and evolution, including the stellar mass and even the stellar distance if we can determine the pulsation indices (k,\ell,m) of the non-radial g-mode light variations observed in compact pulsators. We made tentative identifications for GD 358 using a method based on the frequency distribution of consecutive radial overtone g-modes. A comparison of the amplitude of the pulsation between the optical and the UV proves to be another independent method to identify the pulsation indices. Our project is to apply both methods to GD358. We will measure the optical amplitude with ground-based time series photometry. By observing the DBV star GD 358 with the HST, we have a unique opportunity to cross-calibrate the two methods -- essential if we are to have confidence in the conclusions drawn from either method. The future of asteroseismology of white dwarf stars hinges on these observations. We attempted this science previously with HST. The observations were successful, but GD358 had other ideas (See Justify Duplications section). This exciting data set only adds to the importance of the proposed calibration observation. ================================================================================ Proposal Category: GO Scientific Category: FIELD STELLAR POPULATIONS ID: 8255 Title: Stellar Populations in the Closest Large Low Surface Brightness Galaxy PI: Patricia Knezek PI Institution: The Johns Hopkins University We propose to observe the closest known large low surface brightness (LSB) galaxy, UGC 2302, in order to resolve for the first time the massive stars and tip of the red giant branch in such a system. Large LSBs represent an extreme star formation environment, both locally within their disks, and on a larger scale, often residing in underdense regions of the universe. Resolving the underlying stellar component of such a galaxy can provide critical information on how stars form and evolve in low metallicity, yet gas-rich environments. The combination of this data with planned near-infrared, abundance and molecular gas studies, existing optical UBVRI and HAlpha data, and a VLA HI map, will allow comparison between the abundance and distribution of stars, star formation, and neutral gas in unprecedented detail for disk LSBs. In addition, determination of the characteristics of even the brightest stars in this galaxy will provide a key calibration of the relative contribution of the brightest main sequence, giant, and supergiant stars to the optical and near- infrared colors. This calibration can then be applied to determining the underlying stellar populations of other massive LSB galaxies using broad-band filters. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8256 Title: Deep Helium-Mixing and the Ultraviolet Spectra of Hot Horizontal Branch Stars PI: Wayne Landsman PI Institution: Raytheon STX There is now good evidence that the luminosities and gravities of hot horizontal branch (HB) stars in globular clusters are not correctly described by canonical models of core helium-burning stars. Observations of HB stars in the critical temperature range 4.2<\log T(eff)<4.3 consistently yield gravities about 0.4 dex lower, and Stroemgren u magnitudes about 0.4 mag brighter, than canonical predictions. One possible explanation is provided by Sweigart's (1997) non-canonical models, in which the HB envelope helium abundance is enhanced due to prior deep mixing along the red giant branch. The existence of helium mixing would have important implications for long-standing problems, such as the origin of the HB morphology and the RR Lyrae distance scale. However, the critical HB T(eff) range is also where diffusion models predict a large metal overabundance (due to radiative levitation) in the photospheres of the slowly-rotating HB stars. A large metal overabundance ( Fe/H > 0) could explain the observed Stroemgren u and \logg anomalies, but would also predict distinctive UV spectra characterized by strong metal absorption lines. We propose to ascertain the degree to which radiative levitation affects the observational properties of blue HB stars by obtaining STIS low-dispersion UV spectra of 9 hot HB stars in NGC 6752. This will permit us to disentangle the effects of helium mixing and radiative levitation upon HB properties. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8257 Title: VV Cephei: The Egress from Chromospheric Eclipse PI: Philip Bennett PI Institution: University of Colorado We propose to obtain STIS and FGS1R observations of the long-period (20.3 yrs) eclipsing binary VV Cephei (M2 Iab + B0) as it continues to emerge from chromospheric eclipse. We will also obtain comparison spectra of the similar, but less interacting (and non-eclipsing) binaries KQ Pup and HR 8164. This project is a continuation of the Cycle 7 medium length program ``The 1997/98 Eclipse of VV Cephei'' (GO-7269), which used the STIS high resolution echelle modes to probe the chromosphere of the M supergiant primary. This is done by observing the absorption spectrum of the primary's chromosphere, which appears superimposed upon the companion's early-type continuum. Repeated monitoring of the evolution of the chromospheric absorption spectrum during egress from total eclipse permits the construction of an empirical model of the chromosphere and wind of the M2 supergiant. VV Cep is unique among eclipsing binaries in being sufficiently bright for high resolution spectroscopy. The proposed STIS observations will probe the wind acceleration region; obtaining empirical information here is of crucial importance in understanding the nature of energy and momentum deposition in these cool winds. In addition, we will observe VV Cep with the newly implemented FGS1R in TRANSFER mode in order to obtain relative orbit information, and accurate stellar masses. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8258 Title: A Search for Kuiper Belt Object Satellites PI: Michael Brown PI Institution: Caltech The large number of collisions thought to have taken place in the primordial Kuiper belt suggests that many Kuiper belt objects (KBOs) could have suffered binary-forming collisions similar to that which formed the Pluto -- Charon binary. Detection of such KBO binaries would allow us to measure KBO masses, would help us to understand the past collisional environment of the Kuiper belt, and would give a context to the otherwise unique-seeming formation of the Pluto -- Charon binary. We propose a STIS CCD search for binarity in three known KBOs. The three we target include the largest (1996 TO66), the closest (1996 TP66), and the most eccentric (1996 TL66) known. We have performed deep searches around each of these KBOs with the Keck telescope and have not detected distant satellites; any satellites must therefore be closer than about ~0.5 arcseconds. Collisionally formed satellites analogous to Charon should be at distances of only ~0.2 arcseconds; their detection will require the resolving power and sensitivity of HST. We have carefully constructed an observing program optimized to detect any such very close satellites. ================================================================================ Proposal Category: GO Scientific Category: AGN PHYSICS ID: 8259 Title: The Origin of Blue Wings on NLR Line Profiles PI: Mark Whittle PI Institution: University of Virginia Recent progress in understanding the kinematics of the Narrow Line Region (NLR) in Seyfert galaxies has identified three distinct components --- a high velocity nuclear flow, a more widespread gravitational component, and a jet- accelerated component. In this proposal, we aim to isolate and study the high velocity nuclear flow. The observational signature of this component is the famous `blue wing' found on the OIIILambda5007 lines of almost all Seyfert galaxies. Its ubiquity and amplitude suggest high velocity radial flows are present, together with a source of opacity (dust). Surprisingly, although this feature was the first to be identified, its origin and nature are still unknown. The main stumbling block is its compact size and our ignorance of the location of the dust. In this proposal, we select four nearby Seyferts with exceptionally strong blue wings. Using WFPC2 we map the near nuclear distributions of dust and emission lines, while STIS allows us to track in detail the near nuclear OIII velocity field. Together, these data allow a number of tests of the nature and direction of the near nuclear flow. This is the last zone of the NLR to be understood, and yet it plays a crucial role in carrying that understanding inwards towards the BLR. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8260 Title: Searching for the Hydrogen Reionization Edge of the Universe at 5 1 and to measure their properties. In lenses, the host galaxy is magnified and stretched, improving the contrast with the quasar point source. We propose deep I-band WFPC2 imaging of five lensed systems (z=1.29, 1.59, 2.32 2.55 and 4.50) where rings and arcs of lensed hosts have been detected with NICMOS, to measure accurately the host colors and luminosities. Preliminary results suggest that the hosts (of radio-quiet quasars) are not very luminous (L < L_*). Their properties are more consistent with the evolutionary behavior of galaxies built up through continuous star-formation, rather than fully-fledged ellipticals. Even though the sample is small, lensing may offer the best chance to understand the host properties of the bulk of the high redshift quasar population. As a fringe benefit, resolving the host structure will help to determine the dark matter distribution of the foreground lens galaxies. ================================================================================ Proposal Category: GO Scientific Category: DISTANT GALAXIES ID: 8269 Title: The Morphological Evolution of Field Galaxies at 12. Determining how these two seemingly disparate populations are related is the goal of this proposal, in which we will study how the morphology, bulge, and disk properties of normal luminous field galaxies change from z ~ 2 to z ~ 1. Given the space density and luminosity of L_* galaxies we must survey a large area to provide a statistically significant sample of galaxies. Our sample is complete to K < 20 (drawn from imaging down to K~21.4 at 3Sigma to ensure completeness), and covers roughly 100 arcmin^2, ensuring we have several hundred galaxies more luminous than L_* with 1 < z < 2. Near--IR selection is very well suited for the study of galaxy evolution since the near--IR k-corrections are small, uniform over galaxy types and rather immune to evolution of the stellar population. Thus, the galaxy type mix will be the same for all redshifts, and ensures that the galaxy sample is not biased toward finding more actively evolving populations. ================================================================================ Proposal Category: SNAP Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8270 Title: Proper Motion of the Leo II Dwarf Spheroidal PI: Michael Siegel PI Institution: University of Virginia, Department of Astronomy We propose to continue our investigation into the proper motion of distant satellites of the Milky Way with a series of HST snapshots around faint galaxies within our Leo II astrometric field. We will determine a proper motion for Leo II by combining images from 111 Palomar 200" photographic plates taken by Baade between 1950-1959 with the HST snapshots. Only with the fine pixel scale of HST can we realistically hope to match the exquisite Baade images, which were all taken on the very best nights from a decade of Baade's allotment of about forty 200" nights a year. As part of Siegel's Ph.D. thesis, our project on Leo II will: (1) Determine the proper motion of Leo II with respect to the extra-galactic reference frame, allowing a measurement of the orbital properties of Leo II from 3-D space velocity (1) Develop techniques (of growing importance with the declining availability of photographic cameras and plates) for the astrometric combination of WFPC2 data with older plate material to derive high-precision proper motions. (2) Determine the proper motion for an object at the greatest Galactocentric distance yet attempted, which will provide significant leverage in determining the mass of the Galaxy. (3) Provide a list of proper-motion selected stars for future refinement of the proper motion and parallax of Leo II with the Space-Interferometry Mission. ================================================================================ Proposal Category: SNAP Scientific Category: STELLAR EJECTA ID: 8271 Title: A SNAPSHOT Survey of LMC Planetary Nebulae: A Study of Nebular and Late Stellar Evolution PI: Letizia Stanghellini PI Institution: Space Telescope Science Institute We propose a survey of LMC planetary nebulae (PNe) to study the parallel evolution of the nebulae and their central stars. We will obtain STIS imaging and medium-resolution slitless spectroscopy which will yield line fluxes and nebular morphologies in 7 emission lines (H Alpha, H Beta, \Hei\ <~m 6678 Angstrom, N Ii, O I, O Iii, and [S II]), plus magnitudes of the central stars. We can gather this data very efficiently in a SNAPSHOT survey, and from it we will gather a harvest of information: the nebular size, morphology, ionization structure, density, and mass; and the central star temperature and luminosity (and therefore its evolutionary state and mass). We will test the correlation of nebular bipolarity with large progenitor star mass, and correlate PN morphology and central star evolution in a unique sample of PNe that is free of distance and other biases. We will compare all the observed and derived nebular and stellar properties to the environmental stellar mass function to estimate the progenitor mass. The HST Data Archive has been fully explored to demonstrate the importance of acquiring new data and the feasibility of the program. This study will be the most comprehensive of its kind, and will be unique in the insight it will offer into the combined evolution of PNe and their central stars. Because we expect these data to be of fundamental importance to PN studies, we wave 9 months of our proprietary period to expedite follow-up research. ================================================================================ Proposal Category: GO Scientific Category: FIELD STELLAR POPULATIONS ID: 8272 Title: The Horizontal Branches of the M31 Dwarf Spheroidal Companions And V & VI PI: Taft Armandroff PI Institution: Kitt Peak National Observatory The Galaxy's dwarf spheroidal (dSph) companions show a surprising diversity in the epochs of their major star formation episode(s), extending from ~15 Gyr to ~3 Gyr. To aid in understanding the origin of this diversity, we need similar results for M31's dSph companions, the nearest set of morphologically similar galaxies. Observations of old main sequence turnoffs in the M31 dSphs are impractical, but with WFPC2 we can establish their horizontal branch (HB) morphologies, which observations of Galactic dSphs have shown to be a reliable mean age indicator. Cycle 4 observations indicate that the bulk of the star formation in And I took place ~10 Gyr ago, though the presence of blue HB and RR Lyr stars testify to a minor older component. Analysis of Cycle 6 observations of And II are nearing completion, and observations of And III are scheduled for execution in Cycle 7. Here we seek HST time to complete our study of the M31 dSphs by observing And V & VI, newly discovered M31 dSph companions. The primary aim is to determine the HB morphology and thus fix the epoch of the major star formation episode(s) in these galaxies. Other results that will follow include an estimate of the true (unprojected) distance from M31 and limits on the fraction of younger stars, since the data will reveal any main sequence stars younger than 2--3 Gyr. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8273 Title: The Oxygen Abundance in Translucent Interstellar Clouds PI: David M. Meyer PI Institution: Northwestern University We propose to obtain high-resolution STIS echelle observations of the interstellar O I Lambda1356 absorption toward a sample of stars behind six translucent clouds characterized by large H I column densities and high extinctions (1.10 <=sssim A_V <=sssim 2.82). Previous GHRS measurements of this weak feature in diffuse clouds (A_V <=sssim 1) have shown no evidence of density-dependent O depletion from the gas phase and indicate a total (gas + dust) interstellar O abundance that is about 2/3 of the solar value. Models of translucent clouds predict enhanced depletions of gaseous O into molecules and dust by a factor of 2 or so over those of diffuse sightlines depending on the cloud homogeneity, grain characteristics, and other factors. The primary goals of our proposed investigation are to: (1) accurately determine if the O depletion is enhanced in translucent clouds, and (2) assess the gaseous O abundance spread in terms of extinction variations. With regard to the latter objective, our targeted sightlines sample a wide variety of UV extinction properties and values for the ratio of total-to-selective extinction (3 > R > 5). The lack of any enhanced O depletion among these translucent clouds, especially if the abundance spread is narrow, would signify that the grain characteristics are irrelevant to this issue for extinctions of A_V <=sssim 3. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8274 Title: A Size Survey of Cometary Nuclei PI: Philippe LAMY PI Institution: Laboratoire d'Astronomie Spatiale Following our recent success in detecting and characterizing eight cometary nuclei with the HST, we now propose a minimum program to determine the basic physical properties of a large fraction of the population of short-period comets. By acquiring statistically significant data, we can study the origin of this family of comets and test the hypothesis that they are collisional fragments from the Kuiper Belt Objects, although with much less insight than would be provided by our major proposal emphThe Origin of Short-Period Comets. Our technique takes advantage of the high resolution of the PC2 to clearly distinguish the nuclei from the surrounding comae provided they come within ~2 AU from Earth. Cycle 8 is exceptionally favorable as 13 short-period comets meet this criterion. We also propose to observe the favorably-placed Centaur, 29P/Schwassmann-Wachmann 1, which may be in transition from the Kuiper Belt to the short-period family of objects. Observations will be made through several filters (some combination of U,B,V,R,I depending on the brightness) to obtain unique color information. If appropriate, corrections will be applied to the measured sizes to remove the effect of erosion and retrieve the ``original'' size distribution function. The size and color results obtained during our survey will nearly double the number of cometary nuclei for which this information is available. ================================================================================ Proposal Category: SNAP Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8275 Title: ULTRAVIOLET SNAPSHOTS OF 3CR RADIO SOURCE COUNTERPARTS AT LOW Z PI: William Sparks PI Institution: Space Telescope Science Institute Radio galaxies are an important class of extragalactic objects, representing one of the most energetic astrophysical phenomena, while extraordinarily useful as probes of their environments and of the early Universe. In earlier Cycles we carried out extensive HST snapshot imaging of the 3CR sources to investigate their optical characteristics. Here we propose a major enhancement to a superb dataset: to obtain UV images of the 3CR sources at z < 0.1. A crucial motivation is to offer a zero redshift comparison sample for the extraordinary radio galaxy morhpologies found at high redshift (where UV emission is imaged). Are we witnessing the effects of evolution or of wavelength? We aim to determine whether the alignment effect holds at zero redshift in the UV; we aim to identify regions of star formation along radio axes, associated with dust-lanes, tidal interactions, or elsewhere; we will probe old stellar populations by imaging old hot stars in these predominantly giant ellipticals and measuring radial and isophotal profiles; we will measure brightnesses and frequency of UV nuclei and measure dust extinction through the interesting 2200 Angstrom\ region; we will seek spectral turnovers in known synchrotron jets and hot spots, and may find new ones with increased contrast against the host galaxies. The resulting database will be an incredibly valuable resource to the astronomical community immediately and for years to come. ================================================================================ Proposal Category: GO Scientific Category: SOLAR SYSTEM ID: 8276 Title: UV Spectroscopic Investigation of any Bright, Newly Discovered Comet PI: Harold Weaver PI Institution: The Johns Hopkins University We propose a emphTarget of Opportunity program to investigate any bright comet (mboxV<=6) that is newly discovered during Cycle 8, including comets of any dynamical class. Our main scientific objective is to obtain accurate abundance measurements for all known UV-emitting cometary species (CO from the CO 4PG bands, \cotwo\ from the CO Cameron bands, \stwo\ from the \stwo\ B-X bands, \cstwo\ from CS emissions, and \water\ from OH emissions) and to perform a deep search for any previously undetected species. The long slit capability of STIS will allow us to characterize the spatial distribution of the coma species, so that we can identify those derived from an extended source (e.g. CO), study the decay of short-lived species (e.g. \stwo), and investigate the importance of e-impact on CO for the excitation of the Cameron bands. The latter issue can be definitively resolved during high spectral resolution observations of any comet having mboxV<=5. If an exceptionally bright (V<=2) comet is discovered, we would then request Director's Discretionary time to measure the D/H ratio. This program is a continuation of our efforts in previous cycles to observe as many comets as possible with HST for the purpose of doing abundance intercomparisons on a statistically meaningful sample of objects. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8277 Title: The Kinematics of Knots along Herbig-Haro Jets at High Spatial Resolution PI: Bo Reipurth PI Institution: University of Colorado, Boulder Since the beginning of this decade, it has been speculated that the aligned knots of Herbig-Haro (HH) jets may correspond to ``internal working surfaces'' resulting from a time-dependent ejection velocity. This interpretation has received substantial support from recent HST images of some HH jets, which show that at least some knots do have morphologies that resemble internal working surfaces. However, the principal signatures of a jet with a time- dependent ejection velocity are kinematic, having a systematic spatial velocity variability (with spatial variations over distances comparable to the knot sizes) along the jet beam. Given the fact that the knots have typical sizes (along the jet axis) of ~ 0.5'' and knot separations of ~ 2'', the spatially resolved kinematic characteristics within the knots can only be observed with HST. We propose to obtain STIS spectra of the two better studied HH jets : HH 34 and HH 111. HST images have shown that some of the knots along these jets show the bow shock morphology expected from internal working surface models. The proposed spectroscopic observations will provide the kinematical information necessary for a clear confirmation of the identification of the knots along the HH 34 and HH 111 jets as internal working surfaces. ================================================================================ Proposal Category: GO Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8278 Title: High Precision Photometry of the Core of M13 PI: Charles Bailyn PI Institution: Yale University We propose to obtain highly precise main sequence photometry in V and I in the core of the globular cluster M13. The data will be used to search for a binary sequence, and to obtain highly accurate main sequence ridge lines and a deep luminosity function in the core regions of the cluster. The dynamics and horizontal branch morphology of M13 are anomalous, and it seems likely than an understanding of the core binary population will be required to resolve the problems they raise. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8279 Title: Cataclysmic Variable Disk Winds: a high time- and spectral resolution study of flow inhomogeneity PI: Janet Drew PI Institution: Imperial College of Science, Technology & Medicine Disks and disk winds are found in many astrophysical settings. While much effort has been invested in models for centrifugal MHD disk winds over the past decade or so, only within the past year has the modelling of radiation- driven disk winds developed to the point of generating predictions. This proposed programme of time-resolved UV STIS/E140M observations of the high- state non-magnetic cataclysmic variables (hNCV), IX Vel, V3885 Sgr, and QU Car, will explore a striking prediction of the line-driven wind simulations by Proga et al (1998). These have shown that unsteady, clumped outflow is to be expected where most of the driving luminosity is produced by the disk rather than the central star -- a circumstance believed to apply in hNCV. This programme will identify such clumping as narrow absorption features, first appearing at low outflow velocities, superposed on UV wind-formed spectral line profiles. In addition, these winds, if line-driven, are likely at higher projected outflow velocities to prompt further moving narrow absorption components analogous to those well-known in OB stellar spectra. Flow times are so short (~ 50 sec) in these compact binaries that time-tagged HST/STIS observation is the only option. Observing 3 targets at 3 epochs will both confront theory directly and yield insights into the systematic trends needed to build our understanding of line-driven disk winds. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8280 Title: Origins, Structure and Evolution of Magnetic Activity in the Cool Half of the H--R Diagram: A STIS Survey PI: Thomas Ayres PI Institution: University of Colorado We propose to carry out a major ultraviolet spectral survey of ``coronal'' late-type stars using the powerful capabilities of STIS. The origin of the hot emissions of otherwise cool stars is a fundamental puzzle in astrophysics, and is linked closely with another long-standing mystery, that of late-type winds. Stars are the powerhouses and chemical factories of galaxies. The source of their ionizing radiations and the driving of their mass loss are of paramount importance in studies ranging from population synthesis, galactic chemical evolution, cosmic rays, evolution of planets, to terrestrial ``space weather.'' Magnetic phenomena---at the heart of coronal activity and perhaps wind driving as well---are crucial in many cosmic settings, particularly in dynamic environments such as associated with accretion and mass-transfer. Stars are accessible ``laboratories without walls'' in which to study the interplay of magnetic and plasma processes, and seek a unification with the highly refined---but singular---portrait of the Sun painted by an array of recent orbiting observatories. The missing link: high-quality ultraviolet spectra of a diverse collection of late-type stars. Such a major project was unthinkable before STIS, but the high resolution, broad spectral coverage, and sensitivity of the second generation spectrograph can capture the stellar equivalent of a Hubble Deep Field. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8281 Title: The Spatial and Ionization Structure of Cas A's Metal- Rich Ejecta PI: Robert Fesen PI Institution: Dartmouth College Cassiopeia A (Cas A) is the prototype for the class of young, oxygen-rich SNRs containing material moving at several thousand km s^-1 and exhibiting extreme O and Si-group (Si, S, Ar, and Ca) abundances due to nuclear processing in a massive star. Several basic properties of the remnant are not well understood including shock dynamics of the ejecta, UV and optical line emission mechanisms, and the puzzling organization of its optical knots into large ring -like structures. Here we propose the first high-resolution mapping of this important remnant using WFPC2. Our goal is to survey the small-scale spatial and ionization structures in these metal-rich ejecta, then use these results to test reverse shock and CSM-interaction hydrodynamic and line emission models. We have selected filters which will permit imaging of the remnant's full +/-6000 km s^-1 expansion velocity in both high and low ionization emission lines of sulfur and oxygen. These data will provide spatial information at scales down to 0.001 pc and distinguish oxygen from sulfur rich emission knots and filaments. Because Cas A's ejecta knots have large proper motions of 0.2''-0.5'' yr^-1 and exhibit significant structural changes on timescales of just a few years, we would like to re-image the remnant during Cycle 10 in order to detect and measure spatial and ionization changes. ================================================================================ Proposal Category: SNAP Scientific Category: BINARY STARS ID: 8282 Title: High resolution UV imaging of the binary nucleus of Abell 35 PI: Janet E. Drew PI Institution: Imperial College We propose to obtain two high resolution UV images of the extra-ordinary binary central star of the Planetary Nebula Abell 35 using WFPC2. This system consists of a rapidly rotating G8III-IV star which dominates the optical light, and a PG1159-type white dwarf that dominates the UV flux. It is a challenging test of binary star evolution theories because the interaction between the binary components is apparent in the high rotation of the companion. However, the orbital parameters of the system remain poorly constrained. Our aim is to obtain high resolution UV images of the system with a view to spatially resolving the binary. We already have data indicating a projected separation in the range 0.08-0.14^ without achieving a clear separation of the two stars. The requested observations will improve on this to give direct and more precise measurements of the orbital separation and position angle. These snapshot images will provide first epoch data for the definition of the binary orbit of the central star of Abell 35. ================================================================================ Proposal Category: GO Scientific Category: AGN PHYSICS ID: 8283 Title: High Abundances in Luminous Quasars: A Test Case PI: Jack Baldwin PI Institution: Cerro Tololo Interamerican Observatory Recent studies of high-redshift quasars suggest that their broad emission line regions (BELRs) have metallicities (Z) that are generally above solar. A natural conclusion is that quasars are associated with an epoch of very rapid and extensive star formation during the birth of massive galaxies. However, these metallicity estimates rest on just a few emission lines, most notably N V Lambda1240. We have embarked on a study of other BEL metallicity indicators, especially other nitrogen lines. The N IV Lambda1486 and N III Lambda1750 intercombination lines can be useful abundance probes, but are usually too weak to measure. The only other permitted N line, N III Lambda990, should be an excellent diagnostic but its short wavelength make observations difficult. The quasar Q0353--383 is an ideal test case for all these abundance indicators because the intercombination lines are known to be strong (Osmer 1980). We propose HST-STIS observations to measure N III 990 and other emission lines below LyAlpha to complement our ground-based spectra. The combined data set will complete our reconnaissance of the nitrogen spectrum, measure the gas density and constrain the ionization using abundance- independent line ratios. We will compare results from the various abundance diagnostics, and derive a definitive nitrogen abundance from several stages of ionization. ================================================================================ Proposal Category: GO Scientific Category: AGN PHYSICS ID: 8284 Title: Deep STIS Observations of BALQSO PG 0946+301 PI: Nahum Arav PI Institution: Institute of Geophysics and Planetary Physics A major goal in the study of AGN outflows is the determination of the ionization equilibrium and abundances (IEA) in broad absorption line (BAL) QSOs. In the last few years it has become clear that partial coverage of the continuum source and saturation are common in BALs, and these frustrate attempts to determine the IEA from available HST data because of limitations imposed by the S/N ratio and spectral coverage. We therefore propose to reobserve the most suitable BAL IEA target: PG 0946+301. These observations will allow us to measure saturation using at least six different diagnostics, and therefore derive real column densities. The wide UV spectral coverage will enable us to measure several occurrences of BALs from different ions of the same element which are the key to determining the IEA of the flow. In addition, the combined STIS/FOS data will yield the first possibility of detecting BAL variability in the rest-frame far UV, and the data on the highest ionization BALs will shed light on the connection between the BAL and warm absorber phenomena. This proposal is a crucial part of a multiwavelength campaign on PG 0946+301 which also includes ASCA, FUSE and ground-based observations. Taken together, we believe these data will revolutionize our understanding of quasar outflows. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8285 Title: Using STIS to Unravel Planetary Nebulae PI: William B. Latter PI Institution: SIRTF Science Center/Infrared Processing and Analysis Center/Caltech We propose new STIS observations to study the UV/optical properties of a sample of young planetary nebulae. Objects in this class display remarkable complexity that has prevented a full understanding of post-asymptotic giant branch stellar evolution. With NICMOS we have imaged several such objects in H_2 and other filters. H_2 emission can probe shocks (winds/jets) and the photodissociation region through near-IR emission. To unravel the complex structure (spatial and kinematic) and distinguish between excitation mechanisms (UV or shock), we must follow up our NICMOS observations with STIS. We will use STIS in various long slit modes (low and medium resolution and echelle) to achieve the following objectives: (i) Spatially separate shock structures from radiatively excited regions by looking at diagnostic lines such as ionS2, (ii) obtain kinematic information in the vicinity of the ionized gas--PDR interface and (iii) interpret the spatially resolved results from (i) and (ii) in light of the ``interacting stellar winds'' theories, in which the PN morphology is created as the fast PN wind plows into the slower, denser AGB wind. We require observations with HST to get the highest possible spatial resolution and stability for line ratio studies throughout the complex nebulae. Several emission lines have been selected to be observed at high spectral resolution for measurement of wind velocities and structure. ================================================================================ Proposal Category: GO Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8286 Title: Absolute Proper Motions of Nearby Dwarf Spheroidal Galaxies PI: Edward Olszewski PI Institution: Steward Observatory, U. of Arizona We propose to measure precise absolute proper motions for four dwarf spheroidal satellites of the Milky Way using spectroscopically-confirmed background QSOs to define a zero-velocity reference frame. Three epochs within the 2 years separating 3 HST cycles will yield systemic tangential velocities of UMi, Car, Scl, (and For) to +/- 78 kms\ (+/- 130 kms). These are worst-case velocity precisions and they are likely to be 2* smaller. With 2-3 QSOs per galaxy and 3 observations per QSO field we will have a clear understanding of the systematic errors that could affect the astrometry. We will test whether the halo contains a small number of massive streams containing several dwarf galaxies, or whether the individual halo dwarfs are traveling along independent orbits. HST is essential to achieving the high precisions needed to conclusively compare the projected orbital motions of the individual galaxies; even with our conservative uncertainties, we are competitive with the best ground-based efforts with only a 2 year baseline. We will also use our results to improve our estimate of the mass of the Galaxy interior to ~ 100 kpc. ================================================================================ Proposal Category: GO Scientific Category: QUASAR ABSORPTION LINES ID: 8287 Title: A Search for transparent lines of sight with Intergalactic HeII absorption towards 26 bright z > 2.9 Quasars PI: Dieter Reimers PI Institution: Hamburger Sternwarte We propose to probe the far-UV continuum fluxes of 26 new bright (B~ < 17,5) 2.9 <= z <= 3.2 QSOs from the Hamburg Bright Quasar Survey by means of single- orbit STIS exposure, with the aim of identifying more suitable bright objects for detailed studies of intergalactic HeII absorption over this redshift range. According to improved estimates of the Ly C opacity of the IGM, we expect at least 3 positive detections. Together with 15 FUSE Cycle 1 targets with z < 2.9, successful detections will provide detailed information on the HeII reionization history of the universe which appears to occur close to z = 2.9 and on the diffuse intergalactic medium. ================================================================================ Proposal Category: GO Scientific Category: QUASAR ABSORPTION LINES ID: 8288 Title: UV brightest known intermediate redshift QSO:, A \boldmath z \unboldmath = 1.15 DLA and metals in the Ly \boldmath Alpha \unboldmath forest PI: Dieter Reimers PI Institution: Hamburger Sternwarte We propose to observe with STIS the DLA system at z = 1.15 and the Ly Alpha forest in HE 0515-4414, with V = 14.9 and z = 1.71 the brightest known QSO above z = 1.5 (also in the UV with a flux of > 5 \cdot 10^-15 erg cm^-2 s^- 1Angstrom ^-1). We plan to observe the unabsorbed range from 2300 to 3100 Angstrom\ at a resolution of ~ 30 000 with the following aims: (i) to detect the Ly Alpha forest at z < 1.5 in order to investigate the evolution of metallicity in the Ly Alpha forest by means of optical spectra at extremely high resolution and S/N covering C\IV (z = 1 to 1.5) and Si\IV (1.3 to 1.5); (ii) to determine element abundances in the damped Ly Alpha system at z = 1.15 from ions not accessible from the ground ( H\I, S\II, S\III, P\II, P\V, Si\III, Si\IV, C\II, C \III, O\I, N\II, N\I, Ar\I, etc.). ================================================================================ Proposal Category: GO Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8289 Title: Development and evolution of YSO outflows and jets PI: Christopher Burrows PI Institution: Space Telescope Science Institute XZ Tauri, HL Tauri, and HH 30 are three young stars which can be observed simultaneously in a single WFPC2 pointing. Broad-band HST imaging has revealed that the XZ Tauri binary is the source of an elongated bubble of emission nebulosity nearly 5'' long. In new images of these objects obtained in March 1998, we discovered that the XZ Tau bubble had expanded significantly and had become markedly limb-brightened since 1995. This behavior suggests that we are witnessing, for the first time, the earliest stages of development of a Herbig-Haro bowshock, perhaps the initial formation of its post-shock cooling zone. We propose to test this hypothesis with emission line imaging and temporal monitoring of the bubble's size and brightness. Simultaneously with the XZ Tau study, we will observe the jets and reflection nebulosities of HH 30 and HL Tauri. Monitoring of HH 30 is particularly important, as our 1998 imaging also revealed that a very large reflected light asymmetry has developed in this prototype young stellar object accretion disk system. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8290 Title: Weather, moons, and orbit of the brown dwarf Gl 229B PI: Christopher Burrows PI Institution: Space Telescope Science Institute Gl 229B is the only unambiguous brown dwarf. It can be imaged with high astrometric and photometric accuracy only by HST. For the first time, we have an opportunity to study the object over an extended period of time. The possibilities for detecting planets or moons orbiting Gl 229B are quite promising because Gl 229B's small size, mass, and distance from us amplify the expected signals. We will be able to detect a companion if it is almost as small as Earth, and in a close orbit (similar to those occupied by Jupiter's moons) that is favourably inclined. Such a body in such an orbit might well have formed in the accretion disk from which Gl 229B grew. On the other hand, a higher mass companion in a wider orbit will be detected by the reflex motion it induces on Gl 229B itself, with a search radius limited only by the time baseline over which the observations are carried out. Any detection of a companion will allow the immediate determination of the mass of Gl 229B. An additional benefit of the monitoring proposed here is that if there are stationary and long lived surface features on Gl 229B like Jupiter's giant red spot, we will detect them and hence measure the rotation period of the brown dwarf. Finally, variations in the intrinsic luminosity could be caused by weather in its highly convective atmosphere. Even if no planetary companion is detected, this proposal will establish the variability or lack thereof of this unique object. ================================================================================ Proposal Category: GO Scientific Category: FIELD STELLAR POPULATIONS ID: 8291 Title: The Alpha-Element/Iron Ratio in Starburst Populations PI: Claus Leitherer PI Institution: Space Telescope Science Institute We propose STIS observations of A and F supergiants in NGC1569, the closest starburst galaxy. Spectra around 6200 Angstrom\ taken with the G750M grating will be used to determine element abundances of Fe and several Alpha-elements. The galaxy has experienced a strong starburst over the past few hundred Myr and possibly only very few and much less intense episodes of star formation at earlier epochs. Chemical evolution models predict a significant Alpha/Fe enhancement in the galaxy. This prediction is difficult --- if not impossible --- to verify from an abundance analysis of the gas phase. However, the issue can be settled with a direct abundance measurement in recently formed stars. The proposed STIS observations, in combination with the stellar atmosphere tools we have developed will allow such an abundance determination. These observations are the first abundance measurements of individual stars outside the Local Group. The determination of the Alpha/Fe ratio is fundamental to our understanding of the chemical evolution history of this galaxy. It will also constrain the treatment of mixing processes in the hot and cold phase of the ISM and the enrichment of the intracluster and intergalactic medium. Ultimately, understanding local starbursts in detail will allow us to extrapolate to high redshift and to better understand galaxy evolution in the early universe. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8292 Title: Calibrating the Mass-Luminosity Relation at the End of the Main Sequence PI: Todd Henry PI Institution: Harvard-Smithsonian Center for Astrophysics This is a continuation request for GO 6047/6566/7493. 5pt We propose to use HST-FGS1R to calibrate the mass-luminosity relation (MLR) for stars less massive than 0.2 Msun, with special emphasis on objects near the stellar/brown dwarf border. Our goals are to determine M_V values to 0.10 magnitude, masses to 5\ than double the number of objects with masses determined to be less than 0.20 Msun. This program uses the combination of HST-FGS3/FGS1R at optical wavelengths and ground-based infrared speckle work to examine nearby, subarcsecond binary systems. The high precision measurements with HST- FGS3/FGS1R (to 1 mas in the separations) for these faint targets (V = 10--15) simply cannot be equalled by any ground based technique. As a result of these measurements, we are deriving high quality luminosities and masses for the components in the observed systems, and characterizing their spectral energy distributions from 0.5 to 2.2 Mum. Several of the objects included have M < 0.1 Msun, placing them at the very end of the stellar main sequence, and in fact making them brown dwarf candidates. The payoff of this proposal is high because all 8 of the systems selected have already been resolved with HST- FGS3 during Cycles 5/6/7, and contain most of the reddest objects for which masses can be determined. ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8293 Title: Spatial Structure of Super Star Clusters in NGC 1569 PI: Dan Maoz PI Institution: Tel-Aviv University HST and ground-based observations have revealed that a large fraction of star formation in starburst environments occurs in compact super star clusters (SSCs). SSCs appear to be gravitationally bound, implying a very high star- forming efficiency, which may be difficult to explain. We propose spatially- resolved long-slit spectroscopy of three of the nearest and brightest SSCs in NGC 1569. A fortuitous alignment allows positioning the three SSCs (A1, A2, and B) simultaneously in the slit. The HST + STIS resolution and sensitivity will allow resolving the clusters (half-light radius = 1.6 pc) into three radial bins at 1-4 pc. With our 3000--10,000 Angstrom spectra, we will determine the dominant stellar populations at each radius, and hence the structural star-forming history of the clusters. The only SSC that has been studied in this way is R136 in the LMC, and it shows evidence for population segregation, suggesting the massive stars form last, in the already- established potential well of lower-mass stars. We will test this idea in three additional, more massive, SSCs. The measured radial stellar-population gradient, combined with Keck high-spectral-resolution data will refine the total mass estimate for the cluster and constrain the initial mass function. The mass estimate can reveal the presence or absence of low-mass stars, and thus address the open question of whether SSCs ultimately evolve into globular clusters. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8294 Title: Is SiO observed in the uv spectrum of Beta Gem? PI: Carole Jordan PI Institution: University of Oxford Beta Gem (HD 62509) is a K0 III star with relatively low ultraviolet (uv) emission line fluxes and X-ray emission, and is thought to be a helium core- burning `clump' giant. However, since it lies at a distance of only about 10 parsecs the fluxes at the Earth are sufficient for detailed spectral studies in the uv. Although our main interest in the star has been in modelling for the purposes of establishing and understanding the energy balance requirements, this proposal is concerned with a specific aspect of its spectrum around 2320 Angstrom to 2365 Angstrom. In Beta Gem (HD 62509) and cooler giants the strongest lines in this region are those of C II, Si II and Fe II. The spectrum of Beta Gem (HD 62509) is so far unique in that it also shows a number of narrow emission features that are not observed in the cooler stars, with an overall structure that suggests the presence of a molecular band. We wish to investigate the possibility that this is the A ^1PI - X ^1Sigma (0 - 0) band of SiO, which has never been identified in an astrophysical spectrum. This requires the high spectral resolution of STIS. Other bands in the above system would then also be expected in the region from about 2300 Angstrom to 2500 Angstrom. Chromospheric models would be used to understand the presence of the SiO band system in Beta Gem (HD 62509) and its absence in cooler giants. ================================================================================ Proposal Category: SNAP Scientific Category: BINARY STARS ID: 8295 Title: Anomalously Blue Giants: Possible Precursurs to Subdwarf B Stars PI: Brian Chaboyer PI Institution: Dartmouth College Subdwarf B (sdB) stars are evolved hot stars (24000 to 35000K) that are commonly found in the field of our Galaxy and have recently been identified in old disk, metal-rich clusters. They are likely to be one of the most important contributors to the upturn in the far-ultraviolet (FUV) flux exhibited by many elliptical galaxies and the bulge of M31. It is believed that sdB stars are core helium burning stars with very thin hydrogen envelopes. The mechanism which stripped the hydrogen envelope is not currently known. We propose that sdB stars are formed due to binary interactions. In particular, they have evolved from anomalously blue giants, which in turn have evolved from blue stragglers. These `blue' giants have been recently identified by us in NGC 188 and 6791, and are 0.1 -- 0.2 mag bluer in B-V than the normal red giant stars in each cluster. If our theory is correct, a significant fraction of these giants will have white dwarf companions that could be detected in the FUV. We propose to test this scenario in a snapshot program to obtain STIS FUV images of a dozen of the bluer giants in both clusters. The giants themselves emit a negligible amount of FUV flux and would be undetectable without a hot companion. Confirmation of the presence of hot companions would lend strong support to the theory that the anomalous giants are the binary precursors to the sdB stars. ================================================================================ Proposal Category: GO Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8296 Title: Massive blue clusters in M31 PI: Paul Hodge PI Institution: University of Washington We propose to study six massive blue clusters in M31. U, B, V photometry will provide important data on the stellar population of these clusters, a type virtually unknown in the Milky Way. Comparison of the cluster CMDs with models will allow us to age-date them and to explore the evolutionary parameters, such as stellar mass loss, that are more difficult to study in our Galaxy's much more sparsely-poulated young clusters, which have very few evolved stars in any given cluster. Photometry of the supergiant stars will allow us to constrain the metallicity, one of the probable parameters relevant to the formation of this type of massive cluster. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8297 Title: The Physical State of the Starburst Outflow in NGC1705 PI: Claus Leitherer PI Institution: Space Telescope Science Institute We propose STIS echelle M mode spectroscopy from 1200 Angstrom\ to 3000 Angstrom\ of the nearby starburst galaxy NGC1705. Our selected sightline towards the super star cluster NGC1705-1 probes the physical conditions in the starburst-driven galactic superwind. The resolution of ~10 kms\ is a factor-of -30 improvement over existing HST data and allows a study of the complex outflow kinematics. Multiple supershells are expected to be resolved. Together with FUSE data, the proposed observations will constrain the energetics of the cold and hot gas and help determine if the outflow material can escape from the galaxy. Several weak lines will be measured at sufficiently high S/N to derive column densities and abundances. Previous suggestions of an Alpha- element/Fe enhancement will be verified or rejected using weak Si II, S II, Cr II and Zn II lines. Dust depletion in the outflow will be studied with Fe II lines. No other starburst-driven outflow can be observed with STIS at even remotely similar resolution and S/N. The chosen sightline will allow us to generalize our results to the overall properties of the galaxy outflow, to search for implications for similar galaxies at cosmological distances, and to add to our understanding of QSO absorption lines. We will reduce the proprietary period to six months to allow the community rapid access to these template spectra. ================================================================================ Proposal Category: GO Scientific Category: BINARY STARS ID: 8298 Title: Binary Interaction in the Mira AB Accreting System PI: Margarita Karovska PI Institution: Smithsonian Astrophysical Observatory The Mira AB system belongs to a class of detached binaries in which a compact object accretes mass from the wind of a cool giant or supergiant. This system provides a unique laboratory for detailed study of wind accretion processes because it is the only wind-accreting binary that has been resolved with the HST and whose components can be studied individually. In 1995, we resolved this binary using the HST FOC camera images and objective prism observations. We detected significant asymmetries in the giant's atmosphere and found evidence for possible interaction with its companion. A study of the asymmetric outflow from Mira can be pivotal for understanding the early formation of asymmetries in the atmospheres and the circumstellar envelopes of planetary nebulae progenitors, because Mira-type stars are a critical link in the evolutionary path toward planetary nebulae. We propose to carry out follow up HST observations using STIS to obtain high spatial/spectral resolution observations of each component of the system. Our main scientific objectives are: 1. To further study the signatures of the interaction between Mira A and Mira B; 2. To determine if the asymmetries in Mira A are related to a bipolar outflow or structures in the extended atmosphere; 3. To carry out detailed study and modeling of the accretion processes in the system. ================================================================================ Proposal Category: GO Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8299 Title: Mapping the Dynamics of the quasar 3C 48 PI: Walter Jaffe PI Institution: Leiden Observatory In quasars and radio galaxies there is a relation between the properties of the radio source and those of the (optical) line-emitting gas. Compact steep- spectrum (CSS) radio sources often show disturbed kinematics of the interstellar gas coupled to associated radio components, providing evidence for gas outflow. The interaction between radio jets and the host galaxy ISM may be responsible for the jet confinement to small scales and can contribute to the ionization of the medium and lead to star formation. Detailed study of the circumnuclear region is essential in understanding the processes that drive the kinematics, physical conditions and morphology of the line emitting gas. The archetypical, nearby (z=0.37) quasar 3C 48 is an unusual CSS radio source with excess far-IR emission, whose one-sided radio jet is aligned with the extended ionized emission and a putative second nucleus. The radio morphology and our ground based integral field spectroscopy of 3C 48 suggest the jet is interacting with its immediate environment. 3C 48, because of its high AGN luminosity and proximity, is a good candidate to search for kinematic signatures of the radio jet-gas coupling and/or of a recent interaction. We propose STIS long slit spectroscopy in several slit positions to map the kinematics and physical conditions of the extended emission line gas and their relations to near-nuclear star forming regions found in existing HST images. ================================================================================ Proposal Category: GO Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8300 Title: Testing the Falling Evaporating Bodies hypothesis on the \hb\ star \hd PI: Anne-Marie Lagrange PI Institution: Observatoire de Grenoble It has been recently proposed that several Herbig stars exhibit \spec\ variable features similar to those of the older, Main Sequence star, \bpw, and by analogy attributed to evaporation of cometary-like bodies falling on to the star. The presence of such around Herbig stars is an important issue regarding the evolutionary timescales of planetary systems formation. However, this hypothesis is still controversial and needs to be tested. The only way to do so is to compare the observations with detailed, dedicated simulations, as we successfully did on \bpw. This is also the only way to reliably estimate the physical (sizes, evaporation rates, etc) and orbital parameters of the suspected infalling bodies. We recently adopted this approach in one of the sofar most convincing cases of \hb\ candidates for cometary infalls, namely \hd, comparing IUE data with the predictions of our model. First tests could be done, eventhough limited, due to the limited Signal/Noise provided by IUE and to the limited number of available data. Important differences have already been found between this object and \bpw. We propose to record STIS data to test the cometary hypothesis for this star into more details and more quantitatively, from both dynamical and chemical points of view. ================================================================================ Proposal Category: SNAP Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8301 Title: A SNAPSHOT SURVEY OF X-RAY SELECTED CENTRAL CLUSTER GALAXIES PI: Alastair Edge PI Institution: University of Durham Central cluster galaxies are the most massive stellar systems known and have been used as standard candles for many decades. Only recently have central cluster galaxies been recognised to exhibit a wide variety of small scale (<100 pc) features that can only be reliably detected with HST resolution. The most intriguing of these are dust lanes which have been detected in many central cluster galaxies. Dust is not expected to survive long in the hostile cluster environment unless shielded by the ISM of a disk galaxy or very dense clouds of cold gas. WFPC2 snapshot images of a representative subset of the central cluster galaxies from an X-ray selected cluster sample would provide important constraints on the formation and evolution of dust in cluster cores that cannot be obtained from ground-based observations. In addition, these images will allow the AGN component, the frequency of multiple nuclei, and the amount of massive-star formation in central cluster galaxies to be assessed. The proposed HST observations would also provide high-resolution images of previously unresolved gravitational arcs in the most massive clusters in our sample resulting in constraints on the shape of the gravitational potential of these systems. This project will complement our extensive multi-frequency work on this sample that includes optical spectroscopy and photometry, VLA and X- ray images for the majority of the 210 targets. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8302 Title: Lyman alpha emission in starburst galaxies PI: Daniel Kunth PI Institution: Institut d'Astrophysique de Paris We propose to perform a deep study of Ly-alpha\ emission and destruction in 3 star-forming galaxies. These objects have been already observed with the GHRS and exhibit a variety of situations, with Ly-alpha\ showing P Cyg profiles, secondary emissions or even a deep damped absorption line with no emission. They also span a range of intrinsic properties: IZW18 is a gas-rich, metal deficient dust free dwarf galaxy, Haro 2 has a simple morphology while IRAS 08339+6517 is a luminous IRAS starburst galaxy with more dust and complex Ly- alpha\ profile. The use of STIS will allow for the first time to study the geometrical/kinematical configuration of the ionized and neutral gas across the galaxies nuclear regions and pin point the effects of porosity and the kinematical structure of the ISM, that may play the key roles (in addition to dust) in the detectability of the line. This study will have important impact for cosmology since Ly-alpha\ emitters are nowaday found at high-redshift. We strongly emphasize that since Ly-alpha\ is primarely a diagnostic of the ISM, a full understanding of how the ISM and Ly-alpha\ are related is a necessary step before we can hope to correlate Ly-alpha\ to the cosmic star-formation rate. Our results will be interpreted against the model of superbubble evolution developed with G. Tenorio Tagle. ================================================================================ Proposal Category: GO Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8303 Title: What is 52W036? PI: Steven PI Institution: Majewski University of Virginia, Dept. of Astronomy ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8304 Title: Stellar Winds from Central Stars of Young Planetary Nebulae PI: Sun Kwok PI Institution: University of Calgary Stellar winds from central stars of planetary nebulae (CSPN) are responsible for driving the dynamical expansion as well as shaping the morphology of planetary nebulae (PN). The stellar winds also remove material from the thin hydrogen atmosphere of the central star, determining whether a PN will stay hydrogen burning throughout its lifetime or will go through an episode of thermal pulse and revert back to the asymptotic giant branch. Wind signatures have been seen in the IUE spectra of a number of evolved PN with high temperature central stars but very little is known about the properties of the stellar winds in young PN when the nebular morphology is being shaped. We request HST time to carry out sensitive UV spectroscopic observations of a number of CSPN. With good S/N spectra, we will be able to fit the line profiles of resonance lines to deduce the mass loss rates and terminal velocities of the stellar winds. We propose to observe 4 young PN selected for their small angular sizes, low temperature stars, and high nebular densities. We have chosen a mixture of carbon-rich and oxygen-rich nebulae to see if the wind properties are dependent on atmospheric chemistry. In addition, by fitting the line profiles of some of the atmospheric lines, we can derive the surface gravity and therefore obtain a better determination of the mass and luminosities of the central stars. ================================================================================ Proposal Category: GO Scientific Category: BINARY STARS ID: 8305 Title: Two Post-Common-Envelope Binaries in the Hyades Cluster PI: Howard E. Bond PI Institution: Space Telescope Science Institute V471 Tau and HZ 9 are two detached binaries that are members of the Hyades cluster and consist of hot white dwarfs with main-sequence K-M companions. They have emerged from common-envelope interactions which drastically reduced their initially wide separations. For V471 Tau we will use STIS to confirm and further explore the host of fascinating phenomena that we have found using GHRS in a very limited spectral range near Lyman-Alpha. We have shown that the white-dwarf component, which rotates with a 9.25-min period, has a polar cap of accreted metals. The implied accretion rate from the dK wind, however, is so low that a magnetic propeller mechanism must be rejecting most of the material that attempts to accrete. In fact, we tentatively find Zeeman splitting of a metallic line, implying a field strength of ~350 kG, sufficient for the propeller mechanism to work. The GHRS radial velocities imply a white dwarf mass of 0.85 M_\odot, paradoxically much too massive for the star's high temperature. STIS, whose echelle can cover the entire UV spectrum from 1150- 1710 Angstrom, is ideal for confirming and extending all of these exciting findings. We will also use STIS to obtain the first high-resolution UV spectra of HZ 9, to see to what extent the above phenomena occur in a non- magnetic system which is otherwise remarkably similar to V471 Tau, and to determine accurate component masses. ================================================================================ Proposal Category: GO Scientific Category: QUASAR ABSORPTION LINES ID: 8306 Title: Lyman Alpha clouds toward PKS1302-102. PI: Martin Lemoine PI Institution: Departement d'Astrophysique Relativiste et de Cosmologie We propose to conduct high spectral resolution (DeltaLambda~10 km/s) observations of the low-redshift quasar PKS1302-102 (z_ em=0.278), whose line of sight comprises ~20 Lyman Alpha absorbers with H i column densities in excess of 10^14 cm^-2. Using existing archive FOS data of this quasar, we derived constraints on the average ionization state and metallicity of the absorbers. The constraint is not stringent because the FOS spectrum did not fully resolve the absorption lines. However, when combined with existing upper limits on the local metagalactic ionizing flux, it already suggests that these low-z Lyman Alpha clouds are on average metal-deficient, with Fe/H<~-1. At high resolution, the confidence region for the average radiation flux intensity and metallicity would sharpen considerably and yield a reliable estimate of these two physical characteristics; notably, this would yield an estimate of the baryon content of Lyman Alpha clouds at low redshift. Moreover, three intervening galaxies are present in the field, with impact parameters spanning 40-200 kpc. This line of sight thus provides a unique opportunity, for a relatively low observational cost, to study the morphology and physical conditions of low-z Lyman Alpha clouds, whose nature and origin remain unknown. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8307 Title: Morphology of High Radio Surface Brightness Planetary Nebulae PI: Sun Kwok PI Institution: Department of Physics & Astronomy, University of Calgary The morphological transformation from the spherically symmetric circumstellar envelopes of AGB stars to the complex, bipolar structures of planetary nebulae has remained one of the major unresolved problems in the late stages of stellar evolution. Recent HST observations of proto-planetary nebulae and planetary nebulae have found evidence for jets and radial filaments suggesting that non-isotropic outflows are occuring during the early stages of planetary nebula evolution. However, the morphology of very young planetary nebulae have not been extensively studied by the HST. In this proposal, we have selected a group of compact (< 2^ ) and high radio surface brightness planetary nebulae to image in three narrow bands (HAlpha, N ii, and O iii) to determine the morphological structures as a function of ionization. With these images, we should be able to detect any previously unseen haloes, arcs, jets, and knots, and derive the physical conditions of these features at the earliest stage of PN evolution. ================================================================================ Proposal Category: GO Scientific Category: BINARY STARS ID: 8308 Title: The FUV Spectrum of SS 433 PI: Douglas Gies PI Institution: Georgia State University We propose to make the first ever investigation of the FUV spectrum of the unusual X-ray binary, SS 433, using STIS and its sensitive MAMA detector. The unexplored FUV region should offer significant clues about the nature of the mass-losing star and mass loss by winds. Our plan is to obtain spectra at key phases in the orbital and disk precessional cycles in order to document the spectral variations associated with each of these ``clocks''. We will use a tomography algorithm to separate the FUV spectral features associated with the jets, disk and donor star, and we will compare the optical and FUV light curves to establish the flux contributions from the various parts of this system. Orbital phase variations in the UV P Cygni profiles will provide key information on the role of colliding winds as a source of the X-ray flux. The huge redshifts associated with the jets will translate jet flux from the Lyman limit into the region near LyAlpha, and these variations will help elucidate the radiative processes that drive the jets. The proposed observations offer an exceptional opportunity to study the mass loss processes at this singular stage in binary star evolution. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8309 Title: A Link Between Massive Binary Stars and Non-thermal Radio Emission PI: Debra Wallace PI Institution: The Johns Hopkins University Non-thermal radio emission in Wolf-Rayet (WR) stars is explained in terms of synchrotron emission from shocks in the wind. For single star models, the shocks arise from instabilities in the wind itself, whereas in binary models, the shocks form at the wind-wind interaction zone. In Niemela et al. 1998 (from WFPC2 data), we support the binary theory, for two WR stars, linking the non-thermal emission with the colliding wind region. Before we can conclusively link non-thermal emission to binarity, we must demonstrate that all non-thermal emitters are binary, and that all thermal emitters are either single stars or binary systems with separations that are either too wide or too close to result in a wind-wind interaction that produces shocks. We cannot yet conclusively state this because WFPC2 does not resolve binaries with separations less than about 0.100''. We propose to use the FGS to observe 9 non-thermal and 9 thermal WR stars to search for binary companions. The FGS can resolve angular separations as small as .007''. If the non-thermal stars are resolved as binaries and the thermal emitters are determined to be single, the single star theory of non-thermal emission can be disavowed. Co- latterally, we will have demonstrated a new method of detecting massive binaries, and, for all WR stars, we will establish a more accurate binary incidence rate. ================================================================================ Proposal Category: GO Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8310 Title: White Dwarf Distances to Globular Clusters and the RR Lyrae Luminosity Calibration -- M5 and NGC 3201 PI: Andrew Layden^a PI Institution: Bowling Green State University Despite the efforts of Hipparcos, the RR Lyrae absolute magnitude calibration, M_V(RR), remains uncertain at a level which critically compromises these stars' use as standard candles. This uncertainty propagates into globular cluster ages, Galactic formation scenarios, limits on the age of the Universe, and estimates of the Hubble Constant. Reviewers have concluded that fitting globular cluster white dwarf (WD) sequences to field WDs with observed trigonometric parallaxes, or to theoretical WD cooling curves, has the potential to provide a precise estimate of M_V(RR). However, data on WDs in globular clusters are lacking. We propose deep HST WFPC2 imaging in F555W and F814W of the WD sequences in two nearby globulars rich in RR Lyrae, NGC 5904 (M5) and NGC 3201. We describe our plans for the observations and analysis, and estimate that our resulting M_V(RR) value will be accurate to 0.06 mag (random) plus 0.05 mag (systematic) -- more precise than existing methods. We request parallel imaging observations using STIS to detect variable stars in the cluster. We hope to discover and measure periods of eclipsing contact binaries, which will provide an independent distance estimate. We will also derive deep luminosity functions for these intermediate metallicity globulars. ================================================================================ Proposal Category: GO Scientific Category: DISTANT GALAXIES ID: 8311 Title: MODERATE REDSHIFT ANALOGS TO LYMAN BREAK GALAXIES? PI: Christopher Martin PI Institution: California Institute of Technology We propose to determine whether high luminosity galaxies selected using rest ultraviolet luminosity at low-to-moderate redshift (0.240 in some regions) with 10 km s^-1 resolution that covers 1865 Angstrom to 3100 Angstrom. Recent theoretical work has shown that the neutral hydrogen column density N_ HI of an absorber is tightly correlated with its overdensity, and hence with its dynamical and physical state. However, the mapping between overdensity and N_ HI changes as the universe expands. If we wish to study absorbers at z~1$ that are physically similar to absorbers at z~3 we must probe a factor ~20-50 lower in column density (Dave et al. 1998). The high SNR spectrum obtained from our observations of PG 1634+706 will allow the accurate (10\ uncertainties) measurement of the neutral column densities and line profiles of lines with N_ HI as low as 3* 10^12 cm^-2 and the detection of 87\ 2times10^12 cm^-2 for a significant path length. For the first time it will be possible to study at z~1 the mildly overdense regions of the intergalactic medium that have been observed so successfully at high redshift (z~3) with HIRES and the Keck I telescope. ================================================================================ Proposal Category: SNAP Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8313 Title: Imaging the Host Galaxies of High Redshift Type Ia Supernovae PI: Richard Ellis PI Institution: Institute of Astronomy We propose to obtain snapshot unfiltered STIS images of distant galaxies of known redshift which have hosted supernovae (SNe) of Type Ia found via the Supernova Cosmology Project. The Hubble diagram of these SNe yields measurements of the cosmological parameters (Omega, Lambda) that are inconsistent with a flat Universe of zero cosmological constant. Even if the universe is not flat, Lambda > 0 is indicated with strong statistical confidence (>99\ this confidence is now limited more by the possibility of systematic errors than by statistical uncertainty. In particular, it is important to justify convincingly that effects of the environments of low and high redshift SNe are accounted for by current lightcurve width-color- luminosity correction methods. HST will secure high resolution images to test this hypothesis. We will look for correlations between the luminosity or lightcurve width of the SNe and the host galaxy morphologies and positions of SNe with respect to their host galaxies. We will identify a subset of SNe that are far from the host galaxy, and thus likely to be un-extincted, and use them to obtain an independent check on the effect of extinction on the cosmological parameter measurements. Host galaxy morphologies will also provide new constraints on possible evolution of the SN Ia rate as a function of redshift and galaxy type which can be compared to predictions based on global star formation histories. ================================================================================ Proposal Category: GO Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8314 Title: Star Clusters of NGC 6822 PI: Paul Hodge PI Institution: University of Washington We propose to obtain BVI photometry of four fields in the irregular Local Group galaxy NGC 6822. The chosen fields include star clusters of a variety of ages and we will study the CMDs of both the clusters and the surrounding field stars. Our goals are: (1) to measure the oldest population of stars in the field to answer the question of when star formation commenced in this galaxy; (2) to ascertain the nature of the star formation history of the galaxy; and (3) to look for evidence of a halo population of old stars. ================================================================================ Proposal Category: GO Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8315 Title: The Location of the Active Nucleus in the Radio Galaxy 3C 294 PI: Alan Stockton PI Institution: Institute for Astronomy We have obtained AO K'-band imaging of the z=1.779 radio galaxy 3C 294 showing detailed and intriguing structure within a region a little larger than an arcsecond across. Our bandpass corresponds to restframe 6800--8300 Angstrom, a region devoid of strong emission lines, so it is likely that the structure is dominated by continuum radiation. It is not obvious which (if any) of the numerous knots corresponds to the nucleus, and the correct interpretation of the structure depends critically on its location. The center of 3C 294 lies about 9"\ from a V=12 star, and we know the registration of our image with respect to this star to an accuracy of ~10 mas. Furthermore, the position of the compact flat-spectrum radio core is known from VLA observations to a similar or better precision. However, the position of the bright star is uncertain by at least 0arcs8 (2 Sigma). We need to improve this uncertainty by at least a factor of 6 in order to locate the nucleus with sufficient precision in our image. We propose to use FGS1R to measure the position of the star and three nearby V~15 stars with respect to a bright Hipparcos star, which can be placed simultaneously in the FGS1R pickle. We will use groundbased observations to determine more accurately the HST rotation angle so that we can obtain both coordinates to the required accuracy from the single astrometric standard. ================================================================================ Proposal Category: GO Scientific Category: QUASAR ABSORPTION LINES ID: 8316 Title: The LyAlpha Absorption Cross-Section of Nearby Galaxies PI: David V. Bowen PI Institution: Royal Observatory, Edinburgh We propose to determine the size of Ly-alpha\ absorbing halos around nearby, relatively isolated galaxies, by searching for Ly-alpha\ absorption in STIS spectra of 12 UV-bright, background QSOs and AGNs. The galaxies selected cover a range of luminosities, from M_B = -16.1 to -19.9, and are probed at distances of 4-160 \h\ from their centers. We aim to settle the question of whether galaxies possess extended, gaseous envelopes with radii of several hundred kpc, and whether the presence of Ly-alpha -absorbing gas around a galaxy depends on its luminosity, morphology, or inclination. To test the latter case, for example, we have selected five sightlines which probe highly inclined galaxies: three sightlines are aligned with the major axis of these galaxies, the two others pass >= 45degrees away from the major axis. With these data, we will be able to determine whether absorption occurs in galaxy disks or halos. We wish to obtain spectra with the G140M grating to measure precise column densities of the absorbing gas and thereby map the decline in H I column density with galactocentric radius. The high resolution of the spectra will allow us to accurately determine the velocity of the gas, which can be compared to the systemic velocity of the galaxy, and to the velocity field determined from 21 cm H I emission measurements, when available, enabling us to determine if or how the gas is kinematically tied to the galaxy. ================================================================================ Proposal Category: GO Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8317 Title: Mass accretion rates for pre-main sequence intermediate mass stars PI: Nuria Calvet PI Institution: Smithsonian Astrophysical Observatory We propose to obtain the first direct, accurate measurements of mass accretion rates for intermediate mass (1.5M(sun) to 3.5M(sun)) T Tauri stars (TTS), precursors of the Beta Pic-type stars. Observations in the far and near ultraviolet with the low resolution STIS spectrographs will be used to measure the excess luminosity produced by the accretion of protoplanetary disk material onto the central star. These measurements cannot be made at optical wavelengths for these stars because of the lack of contrast between the excess emission and the photospheric flux. These observations, combined with our accretion shock column modelling, will provide for the first time measurements of the mass accretion rate for intermediate mass TTS. With these measurements and our existing infrared line fluxes, we will extend our present calibrations of accretion luminosity with emission line luminosity for low mass TTS to the entire range of mass covered by these stars. This will provide a powerful tool for rapidly obtaining mass accretion rates for large samples of stars in different evolutionary stages and environments, enabling the effective study of stellar and protoplanetary disk formation and evolution. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8318 Title: Probing the Evolution of Massive Stars: Ejecta Ring Nebulae Abundances and Dynamics PI: Linda Smith PI Institution: University College London We propose to obtain STIS spectra of the nebulae surrounding several evolved massive stars in the Magellanic Clouds. These stars represent a short but key transition phase in the evolution of an O to a Wolf-Rayet (WR) star. This phase is characterized by a sudden increase of the mass loss and the appearance of processed material at the stellar surface. The remnants of this brief period are seen as small circumstellar shells. Since the nebulae, in effect, represent the stellar surface layers during the transition phase, the stellar evolutionary history can be probed by using STIS spectra to measure the N and O abundances together with the dynamics. HST is required because the nebular radii are typically 2--4 arcsec and thus stellar contamination precludes an accurate ground-based analysis. Our previous HST/FOS observations show that one such nebula is not composed of heavily-processed wind material but material that may have originated in a RSG envelope. Since our findings directly challenge our understanding of the evolution of massive stars and their enrichment of the interstellar medium through extensive mass loss, we propose to undertake a systematic abundance study of nebulae around evolved massive stars. This study will allow us to understand at which evolutionary stage the major mass loss occurs in the transition from an O to a WR star, and provide new insights into the LBV mass loss mechanism. ================================================================================ Proposal Category: GO Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8319 Title: Masses and Distances of Pre-Main Sequence Binaries PI: Michal Simon PI Institution: SUNY We propose the continuation of FGS measurements of the orbital motion of young stars successfully carried out in Cycle 7 and earlier cycles. We need to continue these observations to acquire sufficient data to determine the orbital parameters of the binaries. Our goal is to measure the masses of low mass young stars. This will enable a calibration of theoretical calculations of stellar evolution to the main sequence. Hipparcos measured the distance 41+/-10 pc to one of our program binaries, DF Tau, making it an isolated T Tauri star, much closer than its presumed location in the Taurus star forming region at ~ 150 pc (Favata et al. 1998, F98). This measurement drastically changes the conventional interpretations of DF Tau's evolutionary state and its activity. An independent confirmation is urgently required. DF Tau lies well within the capabilities of a reliable parallax measurement using the FGS. We therefore propose parallax measurements of DF Tau and two other binaries in Taurus in our sample. ================================================================================ Proposal Category: GO Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8320 Title: The H_2/CO ratio in the Large Magellanic Cloud PI: Dominik J. Bomans PI Institution: Astronomisches Institut, Universitaet Bochum Little is known about real abundance ratios of the two most abundant molecules H_2 and CO in the interstellar matter of the Large Magellanic Cloud. Because of their abundance, both molecules play a crucial role in the physics of molecular gas. The only possibility to observe the homoeopolar molecule H_2 in its cool phase is the measurement of its far UV resonance lines with absorption spectroscopy., So far, of 4 observed lines of sight to the LMC, only the one to LH 10:3120 showed a significant amount of the H_2 molecule at LMC velocities. The CO molecule also has resonance lines in the far UV, but due to its much smaller amount and the relatively poor signal to noise ratio in the ORFEUS spectrum of LH 10:3120, the presence of CO could not be established from those measurements., With its high resolution spectrograph (STIS), the Hubble Space Telescope provides the possibility to measure several strong CO absorption bands near 1500 Angstrom\ due to the LMC gas. We propose to observe LH 10:3120 and make the direct determination of the H_2/CO ratio for the LMC possible for the very first time. ================================================================================ Proposal Category: GO Scientific Category: AGN PHYSICS ID: 8321 Title: Coordinated STIS/AXAF Spectroscopy of UV/X-ray Absorption in the Seyfert 1 Galaxy NGC 4051 PI: Niel Brandt PI Institution: The Pennsylvania State University X-ray studies of the nearby Seyfert 1 galaxy NGC 4051 reveal strong and complex absorption by ionized nuclear gas (a `warm absorber'). This gas is a major component of the nuclear environment, and we will soon use AXAF to make the first grating-resolution study of the X-ray warm absorber in NGC 4051. Here we propose simultaneous or near-simultaneous STIS UV spectroscopy. Many Seyferts/quasars with X-ray warm absorbers also show UV absorption lines (e.g. LyAlpha, N v and C iv), and it has been argued that the X-ray and UV absorption arise in the same gas. NGC 4051 shows evidence for C iv absorption in IUE spectra, and combined STIS/ AXAF spectra will allow us to critically test the unified UV/X-ray absorber model by comparing the velocity fields and strengths of the UV/X-ray absorption. We will also derive superior constraints upon the internal velocity structure, location, global covering factor, and line-of-sight covering factor of the ionized gas. NGC 4051 is a particularly interesting target because, as a soft X-ray `Narrow-Line Seyfert 1' galaxy, its ionizing continuum is substantially softer than that of more `typical' Seyfert 1s (e.g. NGC 3516 and NGC 3783). This may lead to significantly different absorption characteristics. This observation will be the first HST UV spectroscopy of NGC 4051, and simultaneous observations are important because the absorption is likely to be variable. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8322 Title: The Distance to NGC 2841: Improving the TF Calibration and Definitively Testing MOND PI: Greg Bothun PI Institution: University of Oregon This proposal aims to measure a distance to the spiral galaxy NGC 2841 using Cepheid variables. NGC 2841 provides a unique opportunity to simultaneously probe three separate phenomenon in extragalactic astronomy: 1) It will provide the highest rotational velocity data point for the Cepheid based calibration of the I-band Tully-Fisher relation and thus will firmly determine if this relation experiences curvature or remains linear all the way out to high rotational velocities. 2) It has hosted two SN Ia events; both of which have good photometry (1957A and 1972R)- this significantly adds to the number of calibrators for the SN Ia distance scale; 3) If its distance can be shown to be significantly less than 19.5 MPC, then MOND can be definitively ruled out because NGC 2841 will require a value of a_o substantially in excess of the empirically determined "universal" value. The current estimated distances for NGC 2841 range from 9--20 Mpc. An accurate determination of this distance, based on HST detection and measurements of its Cepheids, will therefore have an important and distinctive impact in these three areas. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8323 Title: Herbig-Haro Jets Irradiated by Massive OB Stars PI: John Bally PI Institution: CASA, University of Colorado, Boulder Despite significant recent advances in the investigation of Herbig-Haro jets powered by young stars, a number of fundamental problems remain unsolved. Among these are the precise determination of the mass loss rate through a jet, and the nature of the flow behavior in the jet launch and collimation region. We have discovered a class of HH jets which are irradiated by the UV radiation from nearby OB stars and are therefore photoionized. Such jets hold the promise of a direct measurement of the mass flow rate through a jet. Furthermore, our observations show that the opaque envelopes that normally obscure jet sources have been removed from these objects. We propose to use HST to study the brightest of these irradiated jets, HH 444. STIS spectra will be used to measure the distribution of electron density, the mass flux through the jet, and the kinematics and excitation conditions in or near the jet collimation region which will constrain models of jet formation. We will also use WFPC2 to determine the sub-arcsecond structure of the jet so that we can correctly interpret the STIS spectra, to search for evidence of a circumstellar disk needed to fuel the jet, and to probe the nature of the asymmetry seen in this jet. ================================================================================ Proposal Category: GO Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8324 Title: The Structure and Kinematics of Irradiated Disks and Associated High Velocity Features in Orion PI: John Bally PI Institution: University of Colorado, Boulder STIS provides us with a unique opportunity to study the early evolution of proto-planetary disks and their chances of survival in the harsh irradiated environments of OB associations where most stars form. We seek to test new circumstellar disk photo-erosion models for the Orion Nebula proplyds (proto- planetary disks), to measure the disk mass loss rates, the nature of their tails, and the high excitation upstream bow shocks (HAlpha + ionO3 arcs). We will obtain long-slit low dispersion UV spectra to measure the relative intensities of a variety of UV lines that trace the excitation conditions in the circumstellar disk, neutral outflow, and in the ionized zone and to search for OH emission predicted by a recent model of photo-chemical excitation of the 6300Angstrom\ ionO1 line. We will obtain moderate resolution long slit visible spectra to constrain the sub-arcsecond structure and excitation conditions in the proplyds, search for disk rotation, estimate disk wind velocities, and measure the flow velocities as a function of position, excitation, and ionization and in various portions of the photo-ablation flow. We will measure the velocity fields of several supersonic micro-jets powered by the Orion proplyds. Our data will constrain the survival time of irradiated disks, address their potential for forming planetary systems, and shed light on the planetary system formation frequency. ================================================================================ Proposal Category: GO Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8325 Title: Galaxy Evolution in Low-Density Environments: WFPC2 Imaging of Poor X-ray Clusters at z=0.2--0.3 PI: Roger Davies PI Institution: University of Durham We propose to use WFPC2 to obtain high quality morphological information on galaxies within 9 X-ray-selected poor clusters at z=0.2--0.3. These morphologies will be combined with information on the stellar populations of the galaxies from our on-going spectroscopic survey of these systems to provide a complete view of the morphological and spectral evolution of galaxies within these clusters. The results of this analysis will be contrasted with the conclusions of previous HST/spectral studies of much richer clusters to provide a clearer understanding of the physical processes which operate on galaxies and how these vary with environment. One Specific goal is to test recent claims that the ram-pressure of the intra-cluster medium causes a morphological and spectroscopic transformation of star forming disk galaxies into S0 galaxies. ================================================================================ Proposal Category: GO Scientific Category: STELLAR EJECTA ID: 8326 Title: Colliding stellar winds and proto-planetary dynamics: WFPC2 imaging of OH231.8+4.2 PI: Valent'\in Bujarrabal PI Institution: Observatorio Astronomico Nacional The interaction between a fast post-AGB collimated wind and a slowly expanding, dense AGB wind is believed to be the dominant dynamical effect in the evolution of protoplanetary nebulae (PPNe) and the shaping of planetary nebulae. We are carrying out a multi-wavelength study of the protoplanetary nebula OH231.8+4.2. Our interferometric mapping of mm-wave molecular lines in OH231.8+4.2 shows the presence of a massive molecular envelope, to which a large amount of momentum has recently been transferred via shock interaction. Long-slit optical spectroscopy reveals the overall kinematics of the shocked high-excitation gas, showing a strong axial gradient superimposed on bubble- like expansion. OH231.8+4.2 is the only PPN known so far in which the leading bow shock has been detected. Because of the rich structure of the shocks in this source, it is the best candidate to study protoplanetary dynamics, but the different components are still poorly resolved in present observations. We propose to use HST/WFPC2 to image with high angular resolution the atomic line emission from the gas component excited by shocks in OH231.8+4.2. These observations will enable an accurate determination of the structure and excitation stratification of the shock fronts and, we argue, will lead to major advances in our understanding of the dynamics of colliding stellar winds and their effect on protoplanetary evolution. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8327 Title: STIS observations of Eta Carinae: The central star PI: Kris Davidson PI Institution: University of Minnesota Eta Carinae relates to a number of astrophysical topics and may be crucial for some of them, but its physical nature is certainly Not Yet Understood, and in 1998 the research situation became even more extraordinary than it was before. New STIS observations had the combination of good spatial and spectral resolution, with UV-to-far-red wavelength coverage, that we've always wanted for studies of the star itself (or its wind). However, these data were acquired during a major ``spectroscopic event.'' It has now become clear that such events recur at 5.5-year intervals, strongly affect the X-rays, and, as the STIS data show, are not easy to explain. Given a 5.5-year periodicity, the binary-vs.\-single-star question has become critical for further progress on Eta Car. If it is a binary, we need to find the parameters. STIS spectroscopy of Eta's normal state is required. Here we propose a project with several combined goals: (1) to obtain the spectrum of the star at ``normal'' times; (2) to extend the wavelength coverage below 1700 Angstrom; (3) to seek evidence for a hypothetical companion star; (4) to learn whether Eta Car varies significantly when it is not near a discrete spectroscopic event; and (5) to study the bizarre spectra of dense, slow-moving, extremely peculiar ejecta located 0.15" to 1.5" from the star. This project is coordinated with our Cycle 7 program and some planned GTO observations. ================================================================================ Proposal Category: GO Scientific Category: HOT STARS ID: 8328 Title: HST ASTROMETRY TO GAUGE THE DISTANCE OF PSR0833-45 (VELA) and PSR 0656+14 PI: Patrizia Caraveo PI Institution: Istituto di Fisica Cosmica del CNR High angular resolution, coupled with sensitivity, makes HST the ideal instrument to measure tiny displacements of faint objects, such as those due to proper motions and annual parallaxes of Isolated Neutron Stars. ,In this proposal, we first include the third exposure of the Vela pulsar aimed at the measure of its parallactic displacement (see GO 6526), then we ask for two more exposures for PSR 0656+14, for which one PC observation, close to the time of the maximum parallactic displacement, is already in hand (GO 6136)., The distance value of both objects is highly disputed and a model-free measurement (or a reliable lower limit) would be very important, e.g., to assess the luminosity of these objects at different wavelengths and measure how efficienctly they convert their rotational energy losses in optical, X and gamma radiation. ================================================================================ Proposal Category: GO Scientific Category: BINARY STARS ID: 8329 Title: Double Degenerates Among DAO White Dwarfs PI: Matthew Burleigh PI Institution: University of Leicester The evolution of DAO white dwarfs, which have hybrid spectra showing both hydrogen and helium lines, is not well understood. It appears that they may be a rather disparate collection of objects with a variety of different origins. For example, it was recently discovered that one of these stars (Feige 55) lies in a close double degenerate system, and must therefore have undergone mass transfer and common envelope evolution. We propose to obtain STIS/FUV spectra of two problematic DAOs, GD561 and PG 1210+533, to determine whether they are also the product of binary evolution. Circumstantial evidence exists to suggest that both stars possess unresolved degenerate companions. However, ground based observations to search for radial velocity variations have proved inconclusive, since the H Balmer lines in these hot stars (50,000K0.01 times solar), a critical test of the model is to find the evolved stars within the population that produced these heavy elements. We propose to search for these stars. Since the model of Blitz et al.\ (1998) predicts HVC distances of >100 kpc, the stars will be faint (V>24). However, we show that they can be found using starcounts on WFPC2 images, provided that the space density exceeds ~1/1000 that in the solar neighborhood, Detecting intergalactic stars in the HI filament would allow a determination of the distance to the HVCs, and establish the presence of a completely new component of the Local Group. A negative result would allow stringent limits to be set on the number of intergalactic stars and on models for HVCs. ================================================================================ Proposal Category: AR Scientific Category: SOLAR SYSTEM ID: 8351 Title: Changes in Uranus' Atmosphere Since the Voyager Encounter PI: Kathy Rages PI Institution: NASA Ames Research Center (Space Physics Research Institute) We propose to combine all the available WFPC2 and NICMOS images of Uranus to investigate the causes of Uranus' long-term temporal variability, including several discrete clouds which apparently have lifetimes of several months. The PI has already developed atmospheric scattering models to fit the Voyager observations of Uranus' southern hemisphere (Rages Etal 1991, Rages and Pollack 1994), and is now modifying them to reproduce the Cycle 6 WFPC2 observations of Hammel et al. We propose to enhance the vertical resolution of the Cycle 6 models by inclusion of the Cycle 7 data of Tomasko et al., and to model observations from previous cycles to investigate the timing of possible changes in (1) the methane cloud's altitude, optical thickness, and single scattering albedo; (2) aerosol absorption below the base of the methane cloud; and (3) height of the putative H_2S cloud at ~3 bars. We will examine northern latitudes up to ~30degrees N to check for possible hemispheric asymmetries in the atmospheric structure. We will also study how the structure of the discrete clouds differs from that of the surrounding atmosphere. The work proposed here complements our previous Cycle 6, approved Cycle 7 and requested Cycle 8 observations of Uranus by (1) extending the wavelength range for modeling of our pre-1998 observations and (2) using data from 1994 and 1995 to partially fill the 10-year gap since the Voyager encounter. ================================================================================ Proposal Category: AR Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8352 Title: Physical Conditions in Predominantly Atomic Interstellar Clouds PI: Steven Federman PI Institution: University of Toledo We propose to determine the physical conditions in interstellar sight lines from archival GHRS spectra showing absorption from C I. The choice of sight lines is based on the fact that observed molecular abundances are relatively low. Analysis of the relative populations among fine structure levels in neutral carbon will yield estimates for gas density and temperature. We will incorporate published results on rotational excitation in H_2 to help constrain the gas temperature. The high quality data on C I, examined with our refined self-consistent set of oscillator strengths, will provide accurate estimates of gas density. We will use the results from C I excitation to further our studies in two areas. We will examine the extent of a separation into low and moderately dense neutral material within a single cloud toward stars in Scorpius and Ophiuchus and whether such stratification is a common feature of interstellar clouds and therefore must be included in studies of interstellar material on galactic scales. We will also obtain information on the amount of CH associated with CH^+ synthesis as an aid to understanding CH^+ formation in the low density portions of interstellar clouds, an unsolved problem despite nearly fifty years of study. ================================================================================ Proposal Category: AR Scientific Category: SOLAR SYSTEM ID: 8353 Title: Constructing a 2-D Picture of Saturn's OH Cloud PI: John Richardson PI Institution: Massachusetts Institute of Technology The discovery of OH changed our view of Saturn's magnetosphere from one where plasma dominated the physics to one where neutrals are dominant. Four different sets of Hubble/FOS observations map the OH emission; published results from two data sets detected OH near the rings at 2 R_S and near the icy moons at 4.5 R_S. These are line of sight observations which determine the OH column density; more information is necessary to convert from column density to number density. We propose to combine all four data sets to reconstruct the OH density distribution. The data encompass 14 different lines of sight at 4 different look angles. The full data set provides much stronger constraints on both the radial and latitudinal distribution of OH than does the published data. Building on past work, we will model the physics and chemistry governing the neutral and plasma densities in Saturn's magnetosphere, and constrain the neutral and plasma distributions observed by HST, Voyager 1, and Voyager 2 to be consistent with our model results. The result of this work will be a 2-D picture of the OH densities in the Saturn magnetosphere, knowledge which is crucial for understanding neutral and plasma sources. Our results will also provide a set of predictions and tools for the Cassini mission experiments, as well as the context for linking data from the Voyager missions, HST observations and the Cassini mission. ================================================================================ Proposal Category: AR Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8354 Title: DIRECT Distances to M31 and M33 Using Detached Eclipsing Binaries and Cepheids PI: Dimitar Sasselov PI Institution: Harvard-Center for Astrophysics We propose to use the archival observations by the HST/WFPC2 in two important galaxies in the cosmological distance ladder, M31 and M33, to identify the variable stars we have already discovered from the ground. The new variables come from our project, called DIRECT, aiming to obtain the distances to M31 and M33 using detached eclipsing binaries and Cepheids. Combining photometry and spectroscopy for a selected subsample of binaries and Cepheids allows us to derive direct distance of high accuracy, which rely on no intermediate steps. We expect to identify 20--30\ HST/WFPC2 images, thus improving significantly their photometry by quantifying systematic effects due to crowding. This should aid in both the accuracy and precision of our direct distance determination to M31 and M33, which are stepping stones for most of our current efforts to understand the evolving universe at large scales. Thus we expect to help in decreasing the HST Key Project's overall uncertainty in deriving the Hubble constant, H_0, by a factor of 2 (or to about 5\ ================================================================================ Proposal Category: AR Scientific Category: AGN PHYSICS ID: 8355 Title: Chemical Abundances and Geometry in QSO Broad Absorption Line Regions PI: Vesa Junkkarinen PI Institution: University of California, San Diego We propose to use archival HST UV spectra to study the chemical abundances in QSO broad absorption line (BAL) regions while taking into account the geometry of the emission/absorption regions and, in particular, partial covering of the background sources by the absorber. Previous studies of BALQSO spectra point to extreme metallicities, 50 to 100 times solar for some elements (Turnshek et al. 1996) and a phosphorus to carbon ratio of around 65 times solar (Junkkarinen et al. 1997). Other studies suggest that the abundances are 1 to 10 times solar (Korista et al. 1996). The extreme apparent metallicities may result from ignoring, in the analysis, complex ionization and partial covering effects (Hamann 1998). The combination of archival HST UV spectra with existing optical spectra (including Keck HIRES spectra) will provide a better test of both the ionization and partial covering effects. The UV spectra include many lines and provide constraints on partial covering especially from saturated lines that are not black. The high resolution Keck spectra of isolated BALs provide extremely accurate absorption templates and give direct measurements of partial covering in narrower components in the BAL outflow. An analysis of BALQSO spectra that includes the background source geometry and partial covering is now needed before the chemical abundances derived from BALQSOs can be considered reliable. ================================================================================ Proposal Category: AR Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8356 Title: Further Insights into Interstellar Dust Grains Using Ultraviolet Polarimetry and Spectroscopy PI: Michael J. Wolff PI Institution: Space Science Institute Understanding interstellar dust and its role in the universe is very important. Virtually all observations of astrophysical objects and their physical processes are affected by the presence of dust either within the system being studied or along its line of sight. We propose a research program that will appreciably enhance our knowledge of dust properties. The 11 Faint Object Spectrograph datasets identified in the proposal represent a significant fraction of all available ultraviolet interstellar polarimetry. These data will be used to probe the connection of the grain size distribution with sightline environment by employing such powerful techniques as the maximum entropy method. We also propose an analysis of the Goddard High Resolution Spectrograph data for HD 147933, one of only two objects with an observed polarized 0.218 micron\ extinction feature. This aspect of our program will derive gas phase abundances for several elements in an effort to provide further insight into the unique nature of this sightline. ================================================================================ Proposal Category: AR Scientific Category: DISTANT GALAXIES ID: 8357 Title: Rest-frame Galaxy Morphology at Intermediate to High Redshifts Using Archival NICMOS Images PI: Ian Waddington PI Institution: Arizona State University \n We propose to investigate the observed infrared morphology of ~10^4 faint galaxies at intermediate to high redshifts observed in ~160 shallow--deep NICMOS H-band images, which sample the restframe optical. Artificial Neural Networks that are well trained on lower redshift WFPC2 BVRI images will provide reliable classifications for H 26.5--27 mag. We will then address the following science goals: noindent (1) Determine the galaxy counts as as function of accurately determined morphological type, providing strong constraints on galaxy evolution models well beyond levels where these can be measured spectroscopically from the ground; noindent (2) Measure the epoch and type-dependent luminosity distribution N(z,mag,type) in the multicolor HDF images, which will directly constrain the evolution of the different Hubble types with cosmic time and trace the physical cause of this evolution at z~1-- 3; noindent (3) Study the numerous compact objects at faint magnitudes, their size distribution compared with that of nearby galaxies in the restframe optical, and their role in galaxy formation; noindent (4) Provide stronger constraints on cosmological parameters (e.g.\ the cosmological constant) from the counts of well classified E/S0's, which cannot be done through the optical counts since the uncertain restframe UV morphology affects the classifications. ================================================================================ Proposal Category: AR Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8358 Title: A COMPLETE CENSUS OF HOT STARS IN GLOBULAR CLUSTERS PI: Wayne Landsman PI Institution: Raytheon STX We propose to assemble a catalog of ultraviolet fluxes and colors for a complete sample of about 4000 hot stars in twelve globular clusters. For these clusters there are available both archival WFPC2 images of the cluster cores, and wide-field (40') images obtained with the Ultraviolet Imaging Telescope (UIT). The UIT data provide a complete census of the hot stars but lack the color information which can only be provided in the cluster cores by high resolution WFPC2 photometry. We will use this catalog of hot stars to explore aspects of their astrophysics that are presently poorly understood. Specifically, we will (1) test evolutionary tracks of hot horizontal branch (HB) stars by comparing number counts of different phases (2) search for radial gradients in the relative populations of extreme HB (EHB) and blue HB stars, (3) search for statistically significant gaps in the temperature distribution of hot HB stars (which can provide key clues to physical processes taking place in red giant branch stars, such as mass loss and deep mixing), and (4) assemble a complete catalog of ``exotic'' hot stars in the twelve globular clusters. ================================================================================ Proposal Category: AR Scientific Category: COOL STARS ID: 8359 Title: The Spatial Location of the Flaring Regions on AB Doradus PI: Frederick Walter PI Institution: State University of New York We request support to analyze 5 hours of GHRS spectra (600 individual spectra) of the C IV lines of the active K dwarf AB Doradus. These data (program 5310) were obtained immediately prior to our 14 hour GTO campaign (program 5181) on this star on 14 November 1994. AB Dor is the prototypical young, active star. Its atmosphere shows indications of domination by a large-scale global magnetic field. We propose to analyze this data set in conjunction with our GTO data and simultaneous photospheric doppler imaging, using tomographic techniques to identify the locations of the flaring regions, and to correlate them with the dark regions identified from optical spectroscopy and photometry. These data bear on the question of whether the large dark regions in active stars are solar-like magnetically-dominated spots, or are regions more like solar polar coronal holes. This investigation may lead to a better understanding of the nature of the stellar magnetic activity in the most active stars. ================================================================================ Proposal Category: AR Scientific Category: INTERSTELLAR AND INTERGALACTIC MATTER ID: 8360 Title: How Opaque Are Spiral Galaxies? PI: Ron J. Allen PI Institution: Space Telescope Science Institute Using HST Archival images in a previous modest AR program, we have developed a new method to calibrate the effects of crowding and confusion from foreground structure on the counts of background galaxies seen through a foreground system. This new method, the Synthetic Field Method, permits us to establish the area-averaged amount of extinction through the entire thickness of the foreground galaxy. No assumptions about the spatial distribution of the obscuring material in the foreground system or about its reddening law are required. We now propose to exploit this method by applying it to deep Archival images of all 17 nearby spiral galaxies obtained earlier with the HST/WFPC2 in the Cepheid distance scale programs. Applying the method to this large sample of spirals will permit us: (1) to decrease the fundamental uncertainty in our results owing to field-to-field variations in the surface number density of the background galaxies, and (2) to begin quantifying the differences in extinction between arms and inter-arm regions, and between the inner and outer parts of spiral galaxy disks. The results of this project will provide the largest study to date of TOTAL extinction in spiral galaxies using background illuminating objects. ================================================================================ Proposal Category: AR Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8361 Title: The Bulge Properties and Fueling Mechanisms of Nearby AGNs PI: Alex Filippenko PI Institution: University of California at Berkeley We recently completed an optical spectroscopic survey of nearby galaxies that has shown that a substantial fraction of all galaxies, especially those of early Hubble type, exhibit active galactic nuclei. Under the assumption that these are powered by supermassive black holes (SMBHs), we conclude that SMBHs appear to be common constituents of many, but not necessarily all, elliptical and bulge-dominated galaxies. We wish to investigate why some galaxy bulges seem more conducive than others to hosting SMBHs, or at least SMBHs with associated activity. We propose to conduct a study of near-IR (NIR) archival NICMOS images of galaxies from a representative sample of ``active'' and ``normal'' disk galaxies (S0--Sc) selected from our spectroscopic survey in order to (1) quantify the bulge luminosity and (2) perform a comparative study of the structural parameters of the bulges detected. The brightness profiles of the central regions can be quantified much more reliably in the NIR than in the optical because of the lower dust extinction and reduced sensitivity to nuclear spiral arms and star-forming regions. In addition, we will use the images to search for small-scale nuclear bars, either stellar or gaseous, as well as nuclear star clusters, both of which have been suggested as possible mechanisms for fueling the central engine. ================================================================================ Proposal Category: AR Scientific Category: STELLAR POPULATIONS IN CLUSTERS ID: 8362 Title: The Cluster Formation Rate in Nearby Galaxies PI: Paul Hodge PI Institution: University of Washington We propose to study the formation rate of star clusters in galaxies in order to understand better the large dispersion in the open cluster specific frequencies found for different galaxies. Our initial emphasis will be on M31. As the nearest giant spiral galaxy, M31 has been the subject of many studies, including many HST programs. The open clusters of this galaxy, however, have been relatively neglected. Although some 400 candidate open clusters of various ages were identified from the ground nearly 20 years ago, they have not been systematically studied since. This is largely the result of the fact that ground-based images do not easily resolve the clusters, making it difficult or impossible to determine their properties quantitatively. With HST it is possible to do useful quantitative studies of open clusters and to realize their usefulness as indicators of star formation rates as a function of time as well as their importance as probes of modes of star formation in different galactic environments. ================================================================================ Proposal Category: AR Scientific Category: SOLAR SYSTEM ID: 8363 Title: An Archival Study of the Quiescent and Disturbed Atmosphere of Saturn PI: Nancy Chanover PI Institution: New Mexico State University We propose to analyze five imaging data sets of Saturn taken between 1990 and 1995 in an effort to compare the quiescent and disturbed atmosphere of Saturn. During this time interval, there were two large convective disturbances that appeared near Saturn's equatorial region. The data taken during the 1995 ring -plane crossings of Saturn provide a uniquely symmetric view of the northern and southern hemispheres in a quiescent state, relatively unobscured by Saturn's ring system. We will first model the vertical structure of the undisturbed atmosphere at latitudes known to exhibit little or no temporal variation using a multiple scattering adding/doubling radiative transfer code. We will use this general atmospheric model to predict what the same latitudes would look like in the 1990 WF/PC Saturn storm data. This will enable us to characterize the effect of deconvolution on the photometric integrity of the data set. Once we determine that the photometry of the 1990 Saturn storm data has been retained, we will use the doubling code to place limits on the vertical extent of the 1990 and 1994 storms. Finally, we will utilize a buoyancy analysis of the two systems to characterize the energy deposited into Saturn's atmosphere by these convective disturbances. This will yield new information about the Saturnian atmosphere that will prove valuable for the interpretation of the anticipated Cassini data sets. ================================================================================ Proposal Category: AR Scientific Category: COOL STARS ID: 8364 Title: Search for Brown Dwarfs around Nearby Stars PI: S. R. Kulkarni PI Institution: California Institute of Technology The recent discoveries of substellar objects, including exoplanets and brown dwarfs, is rapidly revising our earlier pessimistic view of their abundance. The bizarre spectrum of the cool brown dwarf Gliese 229B, with strong features due to water and methane, has been the principal guide to the design of searches for more such objects. However, to date Gliese 229B remains the only cool brown dwarf known. We propose to use the NICMOS snapshot survey of stars within 10 pc of the sun to conduct an unbiased search for companions of these stars, based solely on their proper motions. The principal goal of the NICMOS survey was to find objects similar to the brown dwarf Gliese 229B by using differential imaging with filters which lie in and out of characteristic absorption bands. The survey, however, is limited because it can not establish with certainty that any object fitting the description above is an actual companion of the star nor could it find companions that are different from Gliese 229B. We have an extensive database of optical and near infrared images of the 1'\ fields of view centered on these stars. These images were taken repeatedly at multiple epochs over the past four years. With this data we can easily determine whether any of the point sources in the NICMOS images are common proper motion companions. We will publish all common proper motion companions found. ================================================================================ Proposal Category: AR Scientific Category: STELLAR EJECTA ID: 8365 Title: Measuring Eta Car's Giant Eruption by Modeling Dust Scattering and Emission in the Homunculus PI: Barbara Whitney PI Institution: Prism Computational Sciences, Inc. The goal of this proposal is to determine better estimates of some fundamental quantities of the Eta Car Homunculus through modeling of HST imagery. These quantities are: total mass of the emitting gas and dust, and the latitudinal distribution of dust. The total mass is fundamental because it says something about the kinetic energy of the eruption which, based on the current estimates, now sits right up there with the bolometric luminosity of the star. The latitudinal distribution says something about the nature of the initial mass loss mechanism that caused the outburst. To get at these quantities, we will need to model the image morphology confirming the shape of the homunculus and inclination, model the dust scattering properties, and estimate the dust- to-gas ratio. The wavelength coverage provided by the WFPC2 camera will nicely constrain dust models as the large difference in opacities will sample different optical depths. The narrow-band images will be used in conjunction with imaging models to estimate the gas-to-dust ratio. We will use accurate 3- D radiation transfer codes and hydrodynamic codes as our modeling tools. ================================================================================ Proposal Category: AR Scientific Category: SOLAR SYSTEM ID: 8366 Title: A Critical Extension to Martian Ozone Abundances Using WFPC2 PI: Barbara A. Whitney PI Institution: Prism Computational Sciences, Inc. We propose to use archival WFPC2 data to determine the atmospheric ozone abundances on Mars for a period not well studied by previous efforts. This quantity is a fundamental diagnostic of that planet's atmospheric processes. The multi-year coverage of the WFPC2 data (1995-7) provides information about the latitudinal, seasonal, and interannual variations of Martian ozone column densities. We will focus our efforts on the period from late spring through the end of summer (in the northern hemisphere), with special attention given to low-to-mid latitude regions where coverage is very incomplete. We will model the ozone absorption in the Hartley Band taking into account Rayleigh scattering, dust, and cloud opacities. Our analyses will involve F255W, whose throughput curves are ideal for measurements of the Hartley Band, F336W, and F410M. We maximize sensitivity to small amounts of ozone by examining regions with large atmospheric pathlengths (i.e., near the limb). Artifacts associated with image restoration are avoided by, instead, convolving the models with the relevant point spread function. Our approach, in combination with the unique nature of the requested dataset, will allow for the most accurate and extensive ozone abundances to date for the seasons sampled. The Mars Global Surveyor does NOT have capability to provide such information. ================================================================================ Proposal Category: AR Scientific Category: YOUNG STARS AND CIRCUMSTELLAR MATERIAL ID: 8367 Title: Testing Protostellar Collapse and Outflow Models PI: Barbara Whitney PI Institution: Prism Computational Sciences, Inc. This proposal is to model high-spatial resolution WFPC2 and NICMOS imagery of the Taurus protostars. By applying 3-D radiation transfer codes that include accurate treatment of dust scattering and clumping effects, and 2-D hydrodynamic codes to the best available high-spatial resolution imagery of these sources, we will learn more about the following scientific issues: 1) if the envelope density really matches the rotationally-flattened infall solution, or is it in fact more complicated than that? We will include other infall solutions such as magnetic collapse and collapse from clouds with initial motion. 2) how the outflows shape the cavities and disperse the envelope; we will use hydrodynamic simulations to test if our presumed geometries are physically plausible and produce images that match the observations. 3) how prevalent are multipolar cavities, and 4) the dust properties in protostars. ================================================================================ Proposal Category: AR Scientific Category: DISTANT GALAXIES ID: 8368 Title: Constraints on the Evolution of Dwarf Elliptical Galaxies from Deep HST images PI: Henry C. Ferguson PI Institution: Space Telescope Science Institute The aim of this program is to test models for the late (z <~ 1) formation of dwarf elliptical galaxies. Such late formation arises as a fairly natural consequence of proposed solutions to the ``overcooling'' problem in theories of hierarchical structure formation. Correlations of dwarf galaxy numbers and ages with the density of the environment are also predicted. The data exist now to test such hypotheses. We will construct models of dE galaxy evolution - - constrained to be consistent with color and luminosity distributions in local samples -- and compare them directly to deep HST images of clusters and blank fields. A range of luminosity function shapes and normalizations will be tested to identify those that are consistent or inconsistent with the number counts of dE-like galaxies in blank fields such as the HDF, and in the fields of high-redshift clusters. The models will take into account spectrophotometric evolution, density evolution, the possible morphological transformation of irregular galaxies to dE's, and selection effects. ================================================================================ Proposal Category: AR Scientific Category: BINARY STARS ID: 8369 Title: Evolution of the Symbiotic Nova AG Pegasi PI: Scott J. Kenyon PI Institution: Smithsonian Astrophysical Observatory We propose to study high signal-to-noise FOS and GHRS observations of the symbiotic nova AG Pegasi. We plan to analyze the ultraviolet spectra together with contemporaneous low resolution optical spectrophotometry of similarly high quality. These data will allow us to examine the line and continuum fluxes and radial velocities at several orbital phases for species with ionization potentials ranging from ~ 10 eV up to ~ 100 eV. We expect three main results from this program. (i) Orbital modulation of the emission line fluxes will yield a better understanding of the geometry of the ionized wind of the red giant primary star. This result will test our predictions that low ionization lines form near the red giant photosphere and that higher ionization species lie close to the accreting white dwarf companion. (ii) Emission line radial velocities will help to constrain the wind geometry and may place limits on the mass of the white dwarf. (iii) The continuum and emission line fluxes will test predictions of our non-LTE photoionization code. We have derived order-of-magnitude estimates for the mass loss rate in the red giant wind and placed some limits on the velocity law in this wind from archival IUE spectra. The HST data will yield better constraints on these wind parameters and begin to test hydrodynamical models for wind accretion in detached binaries. ================================================================================ Proposal Category: AR Scientific Category: BINARY STARS ID: 8370 Title: Duplicity and Variability in HST Guide Stars - An FGS Serendipitous Survey PI: Glenn Schneider PI Institution: University of Arizona With the successful completion of AR/5811 we have demonstrated the efficacy of extracting fundamental astrometric properties of stellar systems from HST guiding data. The HST Fine Guidance Sensors (FGS) are capable of revealing duplicity in faint, close binary systems and measuring their position angles and component separations with a precision which far exceeds that which is possible using other techniques. Intensity data which are produced by the FGS PMTs while in fine lock provide high precision relative photometry on rapid time scales. As proposed in AR/5811 we have built a data reduction and analysis pipeline to exploit these capabilities in a serendipitous fashion using HST guiding data. We have recently publish a new duplicity catalog from a search of 4882 HST guide stars observed in 13,979 acquisitions spanning 22 months giving separations, position angles, and relative brightnesses of the individual stellar components. Our pipeline also extracts FGS photometric data in a form which permits examining light curves and power spectra for astroseismological surveys of these stars, while looking for and characterizing variations due to other intrinsic mechanisms. We now propose to take full advantage of the ground-work which has been established by our pilot program by continuing this survey for the large number of guide stars still to be examined, and which will be observed in Cycle 8. ================================================================================ Proposal Category: AR Scientific Category: GALAXY POPULATIONS AND INTERACTIONS ID: 8371 Title: Near-UV Spectra of Andromeda Globular Clusters Compared to Spectral Calculations PI: Ruth Peterson PI Institution: Astrophysical Advances The near-ultraviolet spectrum of an old stellar population offers the best hope for determining its age and metallicity, since it is dominated by stars near the main-sequence turnoff. We have begun the first step towards this goal by calculating spectra from first principles from 2400Angstrom\ to 3200Angstrom\ for late F and early G stars near the main sequence. The calculations span metallicities 0.1 to 5* solar, and agree well at the low end with stellar IUE and HST spectra. Here we propose to compare archival near-UV spectra of four globular clusters in M31 against theoretical composite spectra to be derived from the grid. Calculated spectra for stars of various temperature and gravity will be weighted and coadded at each of several levels of overall metallicity and relative light-element abundance. We will check the validity of each satisfactory near-UV match against the available color- magnitude diagram and optical spectroscopy for each cluster. The results should show, at each cluster metallicity, how accurately age and metallicity may be derived from near-UV spectra alone and what observational requirements on wavelength coverage, S/N, and resolution are entailed for extragalactic objects which cannot be spatially resolved or optically observed. ================================================================================ Proposal Category: AR Scientific Category: FIELD STELLAR POPULATIONS ID: 8372 Title: Massive emission-line stars in nearby galaxies PI: Rene Walterbos PI Institution: New Mexico State University The HST archive contains numerous exposures in HAlpha and continuum light of nearby (< 10 Mpc) galaxies. We propose to analyze these archival images to create a database of massive stars with high mass-loss rates for galaxies of different Hubble types. The catalog is expected to include candidate Luminous Blue Variables (cLBV), Be stars and possibly some Wolf-Rayet stars. The HST data are unique for several reasons: 1) the high spatial resolution and inclusion of continuum exposures allows us to extend successful ground-based searches for stars with high mass loss rates in the MCs, M31 and M33 out to ten times larger distances. Their HAlpha luminosities and continuum emission provide estimates of the mass loss rates; 2) for galaxies out to a few Mpc, the high resolution allows a search for resolved nebulae possibly indicating eruptive mass loss; such nebulae are known to exist around LBVs in the Galaxy and the LMC; and 3) data are available for different galaxy types with a range of metallicities which will ultimately help in testing the ``Conti scenario'' for massive stellar evolution. The number of cLBVs and other extreme mass-loss stars we expect to find, ranges from a few in the closest galaxies to as much as 50 in M101. Finding these objects is an important first step in shedding light on the poorly understood post-main sequence evolution of massive stars. ================================================================================ Proposal Category: AR Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8373 Title: The Evolution of the Mass--to--Light Ratio of Spiral Galaxies PI: Riccardo Giovanelli PI Institution: Cornell University We propose to study the M/L ratio of spiral galaxies up to a redshift of 1/3, using the Tully--Fisher relation. That goal will be achieved by access to HST archival data, which will provide a target list of galaxies to be observed with the upgraded Arecibo telescope at 21 cm. HST images are of paramount importance in the project, as for redshifts higher than 0.1 it is impossible to obtain sufficiently accurate estimates of galaxy morphology and disk inclination with ground--based images. We have cross--referenced the HST data base with catalogs of galaxy redshifts and conclude that a sample of nearly 100 target galaxies suitable for this study can be obtained using the HST archives. ================================================================================ Proposal Category: AR Scientific Category: GALAXY STRUCTURE AND DYNAMICS ID: 8374 Title: The Morphology of Dust Lanes in Barred Spirals PI: Beverly Smith PI Institution: University of Colorado We propose to use the HST archives to investigate gas inflow along bars in spiral galaxies, by studying in detail the structure of the dust lanes along these bars. In nearby galaxies, these dust lanes are typically about 1'' wide (50 pc at a distance of 10 Mpc) and so are unresolved or nearly unresolved on groundbased images. With the unprecedented resolution of HST, however, these features are well-resolved, providing the opportunity to study their structure in detail. These dust lanes trace the inflowing gas, which is difficult to detect directly along bars, and so provide information about clumping, shocks, and cloud formation in the inflowing gas. The HST archives contain a large number of WFPC2 images of nearby spiral galaxies. With these data, we will be able to determine if these lanes are continuous or clumpy and if they are separated into multiple streams. With the large sample of data available, we will be able to determine if the structure varies from galaxy to galaxy and if there are trends (i.e., are the lanes clumpier, weaker, and/or wider in weaker bars? In galaxies without strong circumnuclear star formation?). These data will provide a valuable test of theoretical models of gas inflow along bars, addressing questions about the importance of self-gravity, viscosity, and shocks in driving gas inflow. ================================================================================ Proposal Category: AR Scientific Category: AGN HOSTS AND ENVIRONMENT ID: 8375 Title: ACCRETION DISKS AND DUST DISKS IN ACTIVE ELLIPTICAL GALAXIES PI: Anne Kinney PI Institution: Space Telescope Science Institute We aim here to study the relation between optical/radio nuclear activity and resolvable dust/gas disks in active ellipticals. We will do this by analyzing a complete, unbiased sample of 112 galaxies chosen on a nearly isotropic property, the diffuse radio flux at 178 MHz. In order to understand the significance of the detected dust in the active ellipticals, we will also analyze a control sample of 135 normal ellipticals matched in starlight luminosity and central surface brightness for comparison. The inner dust structures which probe the effects described here appear on very small scales and generally cannot be observed from the ground. The relative position angle between the radio axis and the dust disk serves as a powerful diagnostic; the orientation of the outer dust disk has the potential to reveal the history of a triggering merger, while the orientation of the innermost dust disk reveals the structure of the accretion disk on ~ 10-100 pc scale. Finally, the radio jet indicates the innermost axis which is generated on scales of ~ 100 R_G or less. With a sample that includes FRI's, FRII's (with luminous active nuclei and ``optically dull"), and normal elliptical galaxies, we can test predictions for the causes of activity, current ideas about the dynamics of the gas/dust involved in mergers, and probe the physics of the resulting accretion disks. ================================================================================ Proposal Category: AR Scientific Category: COOL STARSS ID: 8376 Title: A Semi-Empirical Model of the Structured Wind of 32 Cygni PI: Philip Bennett PI Institution: University of Colorado I propose to construct a semi-empirical wind model of the supergiant primary of the eclipsing binary 32 Cygni (K5 Iab + B6 V), using archival HST/GHRS observations obtained at 6 epochs around the December 1996 eclipse. From these observations, I will empirically determine the hydrogen column density structure along each line of sight to the early-type secondary star using the Tau--v method. I will use codes developed for the analysis of HST/GHRS observations of the similar binary Zeta Aur. Successful Tau--v inversion of the UV absorption line profiles requires high spectral resolution and high S/N, limiting the useful data to those from HST/GHRS. Recent HST/GHRS observations of Zeta Aur in Cycles 2 & 5, and of 32 Cyg in Cycle 6, have shown the primary's wind has discrete structure along some lines of sight. However, global flux diagnostics such as UV emission line profiles and radio continuum fluxes, show that the globally-averaged wind is only slightly variable in time, implying most of the observed variability in the absorption lines is on small scales. Semi-empirical mean models of these winds are useful ================================================================================ Proposal Category: AR Scientific Category: SOLAR SYSTEM ID: 8377 Title: Multispectral Investigation of Jovian Cloud Structure PI: Lawrence Sromovsky PI Institution: University of Wisconsin-Madison We propose to use archived HST images of Jupiter, made before and after the December 1995 Galileo Probe in-situ observations, to investigate cloud structure in and adjacent to the probe entry point and in similar regions at other locations. Prior analyses of Jovian cloud structure, having limited constraints to apply to an underdetermined problem, made assumptions such as semi-infinite clouds, equality of single scattering albedos for upper and lower clouds, uniform phase functions for all wavelengths, and specific cloud base locations. We propose to use new constraints on cloud properties and abundance of condensible species provided by the Galileo Nephelometer, Net Flux Radiometer, and Mass Spectrometer, to reduce the solution space for interpreting remote observations. The primary HST inputs into the proposed analysis will be the wavelength-dependent albedo and limb darkening characteristics of hot spot regions and their surroundings, using WFPC2 and NICMOS imaging from UV to 2.3 microns, with varying Rayleigh scattering and gas absorption as probes of vertical structure, and continuum wavelengths as a probe of particle properties. We will also use several Galileo orbiter images to help constrain heterogeneous and vertical structure using the intermediate methane absorption band at 7270Angstrom . ================================================================================ Proposal Category: AR Scientific Category: CLUSTERS, LENSING AND COSMOLOGY ID: 8378 Title: The Globular Cluster Luminosity Function as a Distance Indicator PI: Bradley Whitmore PI Institution: Space Telescope Science Institute We propose to use existing WFPC2 images of nearby elliptical and S0 galaxies to test the reliability of the Globular Cluster Luminosity Function (GCLF) for the purpose of making distance estimates. The `standard candle' of this method is the turnover point of the GCLF at M_V^0 ~eq -7.3 mag. The empirical evidence currently available, mostly from the Virgo and Fornax ellipticals, is that the internal precision of the GCLF turnover is +/-0.15 mag per galaxy, making the method competitive with even the best distance indicators. However, there is tentative evidence that effects such as dynamical evolution and differences in metallicity (among other second-order parameters) may slightly alter the turnover point. This provides the opportunity to reduce the already- small internal scatter of the method still further, and the possibility of better understanding the origin and evolution of globular clusters. We propose to pursue these goals by determining the GCLF for a sample of ~eq 80 galaxies from the archives, and searching for differences in the turnover as a function of cluster color, position within the galaxies, and environment of the galaxy. Our longer term goal is to use this data set to support a proposal using the Advanced Camera for Surveys (ACS) to measure H_0 to within an internal precision of 5\ (external) precision of 7\ ================================================================================ Proposal Category: AR Scientific Category: DISTANT GALAXIES ID: 8379 Title: Search for Emission Line Galaxies in the Near Infrared Using the NICMOS Grism Data PI: Lin Yan PI Institution: Carnegie Observatories NICMOS has produced a wealth of grism spectroscopic data in the 0.8Mu to 1.9Mu wavelength range. To date roughly 650 primary and parallel orbits of grism data have been obtained at high and intermediate galactic latitudes. We propose an archival research program using this database to search for high redshift emission line objects, to measure the global star formation history at various epochs and to study the evolution of field galaxies. We have analyzed nearly all of the G141 grism (Lambda ~ 1.1Mu - 1.9Mu) exposures taken to date by the public pure-parallel program. This dataset reaches 3Sigma flux limits of (1 - 0.2)* 10^-16 erg/s/cm^2 for integration times of 2,000 to 21,000 seconds. The NICMOS data have lower flux limits than all of the previous near-IR emission-line surveys, including those with the Keck telescopes. We have developed expertise in reducing the NICMOS grism data and have identified 33 emission-line galaxies in 83 square arc-minutes of G141 data. In this proposed program, we will: 1) reduce the entire NICMOS grism GO and GTO data sets; 2) search for emission-line objects over ~ 170 square arcmin, roughly doubling our present sample; (3) derive the global star formation history to z ~2; (4) measure the spectral continuum for bright galaxies which don't have emission lines in our observed wavelength range; and (5) make all of the reduced grism data available to the public. ================================================================================ Proposal Category: AR Scientific Category: DISTANT GALAXIES ID: 8380 Title: Star Formation in Galaxies at 0 14 \Gyr. With a correction for the incompleteness of the sample, the number density of such objects is ~ 0.02 pc^-3, or ~ 0.01 msun pc^-3, assuming for their masses a value typical of white dwarfs. Within the uncertainties arising from the small size of the sample, this mass density is sufficient to account for the entire missing Galactic dynamical mass. The present observations aim to confirm this potentially very important finding. ================================================================================