Cycle 11 Abstract catalog (based on Phase I submissions) Generated on: Mon Dec 10 08:39:48 EST 2001 ============================================================================= Proposal Category: GO Scientific Category: Quasar Absorption Lines and IGM ID: 9350 Title: Intergalactic HeII absorption in CSO 118 = HS 1157+3143 PI: Dieter Reimers PI Institution: Hamburger Sternwarte We propose to observe the HeII Gunn-Peterson effect in the z = 3 quasar CSO 118, which has been discovered in our SNAPSHOT survey to have a transparent line of sight. The aim is in particular to extend our knowledge about HeII reionization which has been observed to take place in the range z = 3.1 to z = 2.8. While existing and future FUSE observations will cover the redshift range z < 2.9, redshifts above 2.9 have been covered by HST with only 2 lines of sights. ================================================================================ Proposal Category: GO Scientific Category: Cosmology ID: 9351 Title: Determining Hubble's Constant from Observations of Cepheids in the Host Galaxy of SN Ia 1994ae PI: Adam Riess PI Institution: Space Telescope Science Institute We propose to determine the luminosity of the type Ia supernova (SN Ia) 1994ae by observing Cepheids in the host spiral galaxy NGC 3370. Modern CCD photometry has yielded an extremely tight Hubble diagram for SNe Ia with a precisely determined intercept (i.e., Delta H_0/H_0 ~ 1) measurement of the true Hubble constant is still limited by the calibration. The HST calibration of all but a few SNe Ia observed to date is significantly compromised by the systematics of photographic photometry and host galaxy extinction, as well as by the photometric uncertainties associated with WFPC2. In contrast, SN 1994ae is one of the very best-observed SNe Ia with CCD photometry. The exquisite B, V, $R, and I light curves are well-sampled beginning 10 days before maximum brightness, and they indicate little reddening. From our supernova photometry and the current provisional SN Ia calibration we would find a distance of 30 +/- 2.1 Mpc, well within the range where ACS can accurately observe Cepheid light curves and distinguish Cepheids from nonvariable stars. ================================================================================ Proposal Category: GO Scientific Category: Cosmology ID: 9352 Title: The Deceleration Test from Treasury Type Ia Supernovae at Redshifts 1.2 to 1.6 PI: Adam Riess PI Institution: Space Telescope Science Institute Type Ia supernovae (SNe Ia) provide the only direct evidence for an accelerating universe, an extraordinary result that needs a rigorous test. The case for cosmic acceleration rests on the observation that SNe Ia at z ~ 0.5 are ~ 0.25 mag fainter than they would be in a universe without acceleration. A powerful and straightforward way to assess the reliability of the SN Ia measurement and the conceptual framework of its interpretation is to look for cosmic deceleration at z >= 1. This would be a clear signature of a mixed dark-matter and dark-energy universe. Systematic errors in the SN Ia result attributed to grey dust or cosmic evolution of the SN Ia peak luminosity would not show this change of sign. We have demonstrated proof of this concept with a single SN Ia, SN 1997ff at z = 1.7, found and followed by HST. The results suggest an early epoch of deceleration, but this is too important a conclusion to rest on just one object. Here we propose to use HST for observations of six SNe Ia in the range 1.2 <= z <= 1.6, that will be discovered as a byproduct from proposed Treasury programs for high-latitude ACS surveys. Six objects will provide a much firmer foundation for a conclusion that touches on important questions of fundamental physics. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9353 Title: Direct imaging of the progenitors of massive, core- collapse supernovae PI: Stephen Smartt PI Institution: Institute of Astronomy Modern supernovae searches in the nearby Universe are discovering vast numbers of SNe which have massive star progenitors (Types II, Ib and Ic). The extensive HST (and ground-based) image archives of galaxies within ~20 Mpc enables their individual bright stellar content to be resolved. As massive, evolved stars are the most luminous single objects in a galaxy, the progenitors of core-collapse SNe should be directly detectable on pre- explosion images. Within the last year we have set direct mass limits on the progenitors of two SNe Type II-P by analysing pre-explosion archive images and follow up HST exposures. We have now identified six other recent, nearby SNe which have WFPC2 archive exposures of the site taken before explosion. Additionally, our Cycle 10 SNAP program will double the WFPC2 image archive of nearby galaxies which significantly increases the chances of having multi- colour photometry of pre-explosion sites for future SNe. In this Cycle, we request time on two fronts. Firstly we require imaging of the six SNe with existing pre-explosion data in order to perform exact astrometry of the SNe positions to around 0.05". Secondly, as a follow on from our two successful Cycle 10 programs, we request ToO status for any nearby core-collapse SN which explodes during Cycle 11 and which has pre-explosion HST images. The goal of this proposal is to directly identify the progenitor stars of core-collapse SNe. ================================================================================ Proposal Category: GO Scientific Category: Solar System ID: 9354 Title: Saturn's Atmospheric Structure at Solstice PI: Erich Karkoschka PI Institution: University of Arizona We propose to image Saturn near its solstice with the same 22 WFPC2/NICMOS filters which we imaged Saturn near its equinox about six years ago. Additionally, we propose to use the ACS/HRC with its high ultraviolet throughput and its superior spatial resolution. All filters span a wavelength range of a factor of 10, they cover methane band strengths over several orders of magnitude, and they include the center and wings of the hydrogen dipole absorption near 2 Mum. Thus, they probe many atmospheric levels over five scale heights. The 22 WFPC2/NICMOS filters have proven to provide an excellent probe of Saturn's vertical aerosol structure. The spatial resolution yields several hundred resolution elements in latitude which can be grouped into 10-15 distinct zones. The best viewing of Saturn high southern latitudes occurs at its winter solstice which happens during Cycle 11. The three spacecraft which have visited Saturn flew by near Saturn's equinox, and Cassini will miss the solstice too. HST acquired comprehensive data of Saturn near its last equinox in 1995. The proposed observations will expand this data set to Saturn's solstice and thus provide a unique record of its seasonal variation. ================================================================================ Proposal Category: GO Scientific Category: Solar System ID: 9355 Title: Test of Efficient Subsampling for NIC3 by Smearing Images of Jupiter PI: Erich Karkoschka PI Institution: University of Arizona Several camera/filter combinations of HST do not sample the point spread function with a sufficiently small sampling interval to retrieve the full spatial resolution possible at the wavelength of the filter. This is especially true for the NIC3 camera. Dithering observations by sub-pixels is the standard solution. However, the extra overhead time of dithering can be too long to make dithering feasible for many solar system targets where rotation or relative motion is noticeable during the overhead time. I suggest to test a new method where a single exposure yields 10 dithered images which provide sufficient subpixel information to recover the whole spatial capabilities of HST. I suggest to test this method with Jupiter imaged by eight NIC3 filters. The same eight filters of NIC1 or NIC2 provide the standard for comparison with still exposures. The method lets Jupiter smear across NIC3 by about three pixels during the whole exposure by changing HST's tracking rates. Each interval between readouts of NIC3 provides a dithered image. It is difficult to predict how well the reduced NIC3 images will compare with the still NIC1 images with respect to spatial resolution, but one orbit of HST can test the method. If this method works well, it could be applied to many other future observations. ================================================================================ Proposal Category: SNAP Scientific Category: ISM and Circumstellar Matter ID: 9356 Title: SNAPSHOT survey of the Planetary Nebulae population of the Galactic Bulge PI: Albert Zijlstra PI Institution: Department of Physics The spectacular structures seen in HST images of planetary nebulae (PNe) are generally accepted as originating from hydrodynamical interactions between stellar winds: the interacting-stellar wind model (ISW). Traditionally, the shaping is thought to occur after the star becomes hot enough to ionize the PN. But recent HST images indicate that the shaping may occur earlier, and the newer GISW model puts the shaping during the pre-planetary nebula evolution. The relative importance of both models is not known: GISW shaping will account for some fraction of PNe, but estimates range from 15--100 during the PN phase, especially for the youngest PNe. We here propose an HST SNAPshot survey of compact PNe in the Galactic Bulge, to test these predictions. The Bulge provides the only PNe population for which progenitor masses are known and nebular ages can be measured. In support of these HST measurements we have already measured velocity fields and emission line fluxes. The survey will give an unbiassed sampling of morphologies, and allow evolutionary sequences to be determined to test the ISW versus the GISW model. By-products of the survey will be the determination of nebular masses, diameters and filling factors. We will also obtain the White Dwarf mass distribution in the Bulge, and the initial-final mass function for low-mass stars. ================================================================================ Proposal Category: SNAP Scientific Category: Hot Stars ID: 9357 Title: Towards a global understanding of accretion physics --, Clues from an UV spectroscopic survey of cataclysmic variables PI: Boris T. Gaensicke PI Institution: Universitaets-Sternwarte Goettingen Accretion inflows and outflows are fundamental phenomena in a wide variety of astrophysical environments, such as Young Stellar Objects, galactic binaries, and AGN. Observationally, cataclysmic variables (CVs) are particularly well suited for the study of accretion processes. We propose to carry out a STIS UV spectroscopic snapshot survey of CVs that fully exploits the diagnostic potential of these objects for our understanding of accretion physics. This survey will provide an homogenous database of accretion disc and wind outflow spectra covering a wide range of mass transfer rates and binary inclinations. We will analyse these spectra with state-of-the-art accretion disc model spectra (SYNDISK), testing our current knowledge of the accretion disc structure, and, thereby, providing new insight into the so far not well understood process of viscous dissipation. We will use our parameterised wind model PYTHON for the analysis of the radiation driven accretion disc wind spectra, assessing the fundamental question whether the mass loss rate correlates with the disc luminosity. In addition, our survey data will identify a number of systems in which the white dwarf significantly contributes to the UV flux, permitting an analysis of the impact of mass accretion on the evolution of these compact stars. This survey will at least double, if not triple, the number of high-quality accretion disc / wind outflow / accreting white dwarf spectra, and we waive our proprietary rights to permit a timely use of this database. ================================================================================ Proposal Category: GO Scientific Category: Cool Stars ID: 9359 Title: The Old Star CS 31082-001, the Age of the Universe, and the Nature of the r-process PI: Roger Cayrel PI Institution: Observatoire de Paris We propose to observe the newly discovered r-process-element enhanced star, CS 31082-001 (Fe/H ~ -2.9), in order to determine abundances of the heaviest stable elements, using absorption lines that are only reachable in the near UV. This star is the only halo star for which a uranium detection has been reported, and for which the U/Th chronometer has been used to specify an age limit. In order to improve the accuracy of the age determination from U/Th we require abundance estimates of the daughter nuclides --Pb & Bi-- for which only upper limits have been obtained from ground-based observations. Such estimates will provide crucial constraints on the initial production ratio of U/Th, resulting in a more strict lower limit on the age of this star's progenitor, hence on the age of the Universe. Measurements of 3rd-peak neutron-capture elements, such as Pt, Os, Ir, and Au, all with lines in the 2400-3100 Angstrom range, will expand our knowledge of element synthesis in the early Galaxy. Our recent ESO-VLT data indicate that the neutron-capture elements in this star exhibit different enhancements as compared with the previously known "r-process star" CS 22892-052, an apparent anomaly that must be resolved. CS 31082-001 is the ideal HST target in its class -- it is 4-times brighter than CS 22892-052, and less affected by molecular line blending. Consequently, these HST data will become the reference in all future studies of similar stars. ================================================================================ Proposal Category: SNAP Scientific Category: Galaxies ID: 9360 Title: Paschen-alpha Imaging of a SIRTF-Selected Nearby Galaxy Sample PI: Robert Kennicutt PI Institution: University of Arizona We propose to carry out a NICMOS snapshot survey in the Paschen-alpha (PAlpha) emission line and H-band of the sample of galaxies being observed at 3.5 -- 160 microns as part of SIRTF Nearby Galaxies Survey (SINGS) and a related guaranteed time survey of starburst galaxies. The PAlpha images, accessible only from HST, will be combined with groundbased HAlpha imaging to measure the extinction in the star-forming centers of these galaxies, and obtain robust, extinction-corrected maps of the massive star formation rate (SFR). The PAlpha data by themselves will provide reliable `extinction-free' SFRs, and a cross- calibration of the (dust--affected) HAlpha-- and UV--based SFRs. The PAlpha-- based SFR measurements will extend the SFR-vs.-gas density law (Schmidt--law) to surface densities at least 30 times higher than what is accessible using HAlpha--based SFR measurements alone, bridging the gap between normal galaxies and IR--luminous starbursts. Furthermore, the combination of the HST PAlpha images with the SIRTF images and spectra, as well as ancillary ground--based UBVRIJHK images and GALEX UV images being obtained as part of the SINGS project, will provide a definitive study of the radiative transfer of starlight and dust heating in star--forming galaxies. The processed NICMOS images will be incorporated into the public SINGS Legacy Data Archive, to enable scores of follow-up studies by the astronomical community at large. ================================================================================ Proposal Category: GO Scientific Category: Stellar Populations ID: 9361 Title: Searching for Primeval Galaxies: the promising case of SBS 1415+437 PI: Alessandra Aloisi PI Institution: The Johns Hopkins University Do primeval galaxies exist in the local Universe? The best candidates are extremely metal-poor (Z <=sssim 1/20 Z) blue compact dwarf (BCD) galaxies whose photometric and chemical properties are consistent with a stellar population younger than 100 Myr. SBS 1415+437 (Z = 1/21 Z) is the closest candidate: its proximity (d = 11.4 Mpc), detailed spectroscopic knowledge of its HII regions and low metal content, used to infer the primordial ^4He abundance, make it the best target for this investigation. We propose to take deep exposures of SBS 1415+437 with the ACS in the F814W and F606W filters. This instrument has resolution and magnitude limits allowing us to reach and resolve with the required accuracy individual stars 1 mag below the tip of the red giant branch (RGBT). If present, these stars will provide a clear sign of an old stellar population (with ages >~ 1 Gyr) and an independent distance indicator. If absent, this will unambiguously show that the system has started to form stars only recently and can be considered the first robust case of local primeval galaxy. We propose to take exposures in the F658N (HAlpha Lambda6563) and FR505N (HBeta Lambda4861) filters to study the morphology of the ionized gas through HAlpha emission and map the dust content with the HAlpha/HBeta ratio in order to solve the age-dust degeneracy of the photometry by constraining reddening effects. ================================================================================ Proposal Category: GO Scientific Category: AGN/Quasars ID: 9362 Title: STIS Observations of the Intrinsic UV Absorption in the Dwarf Seyfert Nucleus of NGC 4395 PI: Steven Kraemer PI Institution: Catholic University of America The Sd IV dwarf galaxy NGC 4395 is one of the nearest (d ~ 4.2 Mpc) and least luminous (L_bol ~ 10^41 ergs s^-1) examples of Seyfert 1 galaxies. Furthermore, it is the only known example of an active nucleus within a bulgeless, extreme late-type galaxy. This unique object possesses all of the classic Seyfert 1 properties in miniature, including broad and narrow emission lines and highly variable X-ray emission, presumably powered by a small (few x 10^4 M) black hole. Furthermore, we have discovered evidence for blueshifted, intrinsic absorption lines in the UV (C IV LambdaLambda1548.2, 1550.8), while X-ray spectra show the presence of bound-free edges from O VII and O VIII. We propose HST/STIS echelle observations to determine the properties (ionization states, column densities, velocity coverages, covering factors) of the intrinsic UV absorbers in NGC 4395. Due to the high covering factor of its narrow-line emission, NGC 4395 offers the best case for testing the connection between the absorbers and the narrow-line region (NLR). Furthermore, an empirical comparison of its absorption properties with those in higher luminosity active galactic nuclei (AGN) will provide valuable constraints on dynamical models of the absorbers, which make predictions that are strongly dependent on luminosity and/or central black hole mass. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9363 Title: Ultra Low Surface Brightness Galaxies PI: Nelson Caldwell PI Institution: Smithsonian Astrophysical Observatory Extremely low surface brightness galaxies have been detected in the Virgo cluster, which are 2 magnitudes fainter than any previously known in that cluster or even in the Local Group. ACS images of three of these should resolve stars at the giant branch tip, and allow us to determine distances, mean metal abundance of the stars, and rough ages. Confirmation of the nature of these galaxies will provide evidence that dark matter halos are pervasive in the universe, extending to galaxies with stellar densities 6 times lower than currently known. These resolved stars would be the most distant yet observed accurately by HST. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9364 Title: The Parallaxes and Proper Motions of Two Nearby Neutron Stars PI: David Kaplan PI Institution: California Institute of Technology We propose to measure the parallax of two nearby neutron stars to the highest possible level of accuracy, 0.5 mas. The primary goal is to determine the neutron-star radius at infinity with better than 1km precision, and therewith obtain a direct constraint on the equation of state of matter at supra-nuclear density. The required flux and temperature determinations are easiest for the so-called isolated or radio-quiet neutron stars because of their apparently completely thermal spectrum. We argue that the importance of the possible results warrants a study to the best possible level of the best possible sources, and request 24 orbits for the two brightest isolated neutron stars, RX~J1856.5$-$3754 and RX~J0720.4$-$3125. We will also determine whether the enigmatic RX~J0720.4$-$3125 is an old magnetar or an accreting source, based on its luminosity and proper motion. ================================================================================ Proposal Category: GO Scientific Category: AGN/Quasars ID: 9365 Title: Spectroscopy in the Inner Region of the 3C 48 Host Galaxy PI: Alan Stockton PI Institution: Institute for Astronomy As far as we are aware, there is only one host galaxy continuum feature in a luminous QSO that is bright enough for practical STIS spectroscopy: this is the bright peak ~1" NE of the well-known quasar 3C 48. This feature (3C 48A) is enigmatic, with an apparently distorted morphology. It may be the distended nuclear region of one of the galaxies in this major merger. It might, instead, possibly be the result of interaction of the compact-steep spectrum radio jet with ambient material; but this seems unlikely because the correspondence between the radio and optical morphologies is not very good. We also know from ground-based and HST imaging that 3C 48A is overwhelmingly dominated by continuum radiation, not line emission, and the colors seem to be inconsistent with stars as young as the probable age of the radio jet. Our previous high S/N ground-based spectroscopy of 3C 48 covered most regions of host galaxy beyond ~2" from the QSO. From this spectroscopy and spectral synthesis models, we have been able to determine mean ages for recent starbursts in various parts of the host galaxy as well as the velocity field of the stars. By tying the proposed STIS spectroscopy of 3C 48A to our existing spectroscopy of the host galaxy, together with archival PC images, we expect to be able to determine the nature of this unusual inner structure and its role in the evolutionary history of 3C 48. ================================================================================ Proposal Category: GO Scientific Category: ISM and Circumstellar Matter ID: 9366 Title: H_2 Imaging of Proto-Planetary Nebulae: Probing the Dynamics and Morphology PI: Bruce Hrivnak PI Institution: Valparaiso University H_2 emission provides an excellent probe of the physical conditions in planetary nebulae (PNs) and also in proto-planetary nebulae (PPNs), objects in transition between the asymptotic giant branch (AGB) and PN phases. It is thought that the shaping of the PN occurs when a fast wind interacts with the remnant of the AGB progenitor during the PPN phase. The study of shock- excited H_2 in PPNs will allow us to study this process. We request HST/NICMOS H_2 and complementary K and H broad-band images of 13 PPNs with a range of spectral types of the central star. We presently have very high-resolution (~100,000) H_2 spectra for 7 of these, which we will use with the high- resolution images to study the velocity structure of the fast wind. We will also explore the relationship between the presence of H_2 and a bipolar shape for the nebula, as has been found in PNs. However, the role of the equatorial torus is expected to be different in these two cases, and in the PPNs it is expected to collimate the wind rather than shield the molecules. Thus the H_2 in the PPNs is expected at the ends of the lobes rather than in the torus. Radiatively-excited H_2 emission appears to be common in PPNs with central stars of B spectral types; this appears to be a transitional stage in the evolution of the H_2 in the nebula which these images will help us to better understand. ================================================================================ Proposal Category: GO Scientific Category: Quasar Absorption Lines and IGM ID: 9367 Title: Unique Opportunities to Search for the Optical Counterparts to High-Z Damped LyAlpha Systems PI: Cyril Hazard PI Institution: University of Pittsburgh The galaxies responsible for damped LyAlpha absorption in QSO spectra are difficult to observe against the strong background QSO emission. We propose to detect even low luminosity galaxies associated with QSO absorption line systems out to redshifts as high as z = 1.8 by observing them in the shadow cast by an even higher redshift damped LyAlpha absorber. As a result the galaxy will be observed free of contamination by the background AGN and of the uncertainties which arise when image processing techniques are required to remove the AGN emission. We propose two approaches. In the first we will attempt to detect a z = 1.8634 system seen in the optical spectrum of a high-z BL Lac object in the shadow of two higher-redshift systems seen in the same optical spectrum. In the second only the higher redshift shadowing LyAlpha system is seen in the optical spectrum and the presence of the lower-redshift systems at z = 0.713 and z = 1.0466 are inferred from the presence of strong MgII, SiII and FeII absorption lines. ================================================================================ Proposal Category: GO Scientific Category: Cool Stars ID: 9368 Title: Spectrophotometry of Procyon A: Testing Metal Opacities PI: Carlos Allende-Prieto PI Institution: University of Texas Metal opacity shapes the near-UV spectrum of late-type stars, which dominate intermediate and old stellar populations. Learning the details of how metal opacity blocks the light in this spectral region is of capital importance to understanding the energy balance in the atmosphere of these stars and, ultimately, building reliable models to interpret observed fluxes. The model atmospheres most used in spectroscopic analyses of individual stars and at the core of population synthesis codes are based on calculations of photoionization cross-sections from the 70's, when better data have been available for a long time. We implement modern cross-sections in our calculations of synthetic fluxes and model atmospheres, but the models need to be confronted with observations. Detailed absolute fluxes for stars of known effective temperatures and angular diameters can constrain the opacities directly from observations. So far, such high-quality UV observations are available only for the Sun, and this leaves some room for ambiguity between line and continuum opacity. Observations with identical quality are possible with STIS for a second nearby late-type star: Procyon A. This star is indeed the only relatively unevolved late-type star for which an extremely precise determination of its angular diameter is available. ================================================================================ Proposal Category: GO Scientific Category: Cool Stars ID: 9369 Title: A Direct Test for Dust-driven Wind Physics PI: Alex Lobel PI Institution: Smithsonian Astrophysical Observatory We propose to perform with STIS a critical test of the physical mechanism of wind acceleration by dust drag in cool stars. Spatially resolved spectra of the circumstellar environment of Alpha Ori (M2 Iab) will directly test if radiation pressure onto dust grains provides the momentum that causes the high mass-loss rates (up to 10^-6 M_odot yr^-1) observed in asymptotic giant branch and red supergiant stars. Terminal gas outflow velocities of 13-14 km,s^-1 are observed in Betelgeuse's circumstellar dust shell. However, the smaller chromospheric outflow velocities (below 6 km,s^-1), point to an extended region in the circumstellar environment where the wind accelerates. Stellar wind theory suggests radiation pressure onto dust grains as the driving mechanism that drags the gas outflow to these high terminal velocities. Dynamic radiative transport calculations that fit the star's 9.7 Mum silicate dust emission indicate that this wind accelerating region is located between 0.78" and ~3". We propose to use STIS to obtain a high-resolution spatial and spectral raster scan across this region. These data can only be obtained for this unique nearby supergiant with the exceptional capabilities of the STIS. An increase of the observed asymmetry of the self-absorbed Mg ii h line (which forms in an expanding gas shell) with distance from the star, will directly confirm (or reject) the theory of dust-driven wind acceleration in cool stars. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9370 Title: The Optical Counterpart of an Ultraluminous X-Ray Source PI: Joel Bregman PI Institution: University of Michigan Ultraluminous X-ray sources (ULX) are non-nuclear sources in normal disk galaxies that are second only to AGNs in point-source luminosity. These enigmatic objects are thought to be intermediate mass black holes (10^3 -10^4 M), and this can be verified by a direct mass determination, which requires knowledge of the mass of the secondary and the period of the binary system. The first step in determining the mass of ULXs is the optical identification of the secondary and for the ULX in NGC 5204, the optical counterpart is a compact blue object at V = 20.3. This counterpart, with M _V=-8.7, is either a very tight cluster of O stars, a megastar, or a background BL\Lac object. We can distinguish between these possibilities with UV spectroscopy and imaging, and for the first time, determine the mass of the secondary in a ULX system. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9371 Title: A Definitive Test of the Nature of SN 1961V: Supernova vs. Luminous Blue Variable PI: You-Hua Chu PI Institution: University of Illinois The most massive stars evolve into luminous blue variables (LBVs) and end their lives in supernovae (SNe). Studies of the late evolutionary stages of the most massive stars will aid our understanding of the chemical enrichment and stellar energy feedback in a galaxy. The final days of the most massive stars can be confusing, as LBV outbursts often mimic SN explosions. The nature of three SNe have been called into question: SN 1954J and SN 1997bs are most likely LBVs, but the nature of SN 1961V is still debatable. SN 1961V is a peculiar SN in a complex environment. Its decaying nonthermal radio emission is consistent with a radio supernova, while its optical light curve and initial expansion velocity suggest an LBV outburst similar to Eta Car. HST WFC1 images could not conclusively identify the LBV. SN 1961V is either a bona fide SN related to exotic hypernovae or failed supernovae, or a superluminous LBV that is the most massive star known. We request STIS observations, necessary for their high spatial resolution, to use emission lines to identify LBV candidates and to discriminate among LBV ejecta nebula, decades-old SN/SNR, and mature SNR that are present within 1" from SN 1961V. We further request WFPC2 images in V, R, and I bands to search for red stars similar to Eta Car and to study the stellar populations in the vicinity of SN 1961V. ================================================================================ Proposal Category: GO Scientific Category: Stellar Populations ID: 9373 Title: Reaching the Horizontal Branch in NGC 5128: Deepest Probe of a Giant Elliptical PI: Marina Rejkuba PI Institution: ESO NGC 5128 is the nearest easily observable giant E galaxy, and is a unique testing ground for stellar population models. Previous WFPC2 photometry of its halo red-giant stars has shown that they are predominantly metal-rich (<~nglem/H rangle ~eq -0.45), but little is yet known about their spread in ages. With the ACS/WFC camera, we propose to obtain deep (V,I) photometry down to the level of its horizontal-branch population, with the goal of refining the metallicity distribution function and gaining quantitative information on its age distribution. This will be unique data for any giant elliptical galaxy and will provide major new input to population synthesis techniques for such galaxies. ================================================================================ Proposal Category: GO Scientific Category: Star Formation ID: 9374 Title: The FUV Flux Irradiating the Surfaces of Protostellar Disks PI: Edwin Bergin PI Institution: Smithsonian Astrophysical Observatory We propose to use STIS to determine the Far-Ultraviolet (FUV) radiation field in 3 proto-planetary disk systems. These systems: LkCa 15, GM Aur, and DM Tau, are among a handful of sources that can be subjected to detailed chemical studies with the current generation of millimeter-wave instruments. Such studies have found that the disks have a rich molecular chemistry, which appears to be controlled by the FUV radiation field (Qi 2001; Dutrey et al 1997; Kastner et al 1997). These observations will allow, for the first time, a firm characterization of the FUV radiation field impinging on the surfaces of circumstellar disks. Knowledge of the FUV field for each object will allow for theoretical chemical models to be created specific to each object and compared to observations. Since these objects will remain, for some time, the main templates for chemical studies of extra-solar disks this project will provide the real UV data required to push theory forward. Given that molecules are excellent probes of their environment, the new information will place better constraints on the virtually unknown vertical structure of proto- planetary disks. This project is unique in scope and will increase our limited understanding of disk chemical evolution, but also improve our knowledge of uncertain physical processes, such as the possible dissipation of outer disks by photo-evaporation and on the timescales of dust grain growth. ================================================================================ Proposal Category: GO Scientific Category: Cosmology ID: 9375 Title: The Host Galaxies of Time Delay Lenses: , An Independent Route to the Hubble Constant PI: Christopher Kochanek PI Institution: Smithsonian Astrophysical Observatory Because of its importance in setting the distance scale, the time scale and in estimating cosmological parameters from the CMB, astronomy needs an estimate of the Hubble constant independent of the local distance scale and its systematic problems. This can be achieved using gravitational lenses with time delay measurements given enough constraints on the gravitational potential of the lens. We will use deep NICMOS observations of the lensed quasar host galaxies in 7 gravitational lenses with time delay measurements to obtain the necessary constraints, determine the dark matter distribution and estimate H_0. Analysis of the existing images and the well-developed theory for analyzing Einstein ring images of host galaxies suggest the new data will break the familiar degeneracies between lens mass distributions and the Hubble constant. We also request 30 ksec Chandra ACIS images for each of the 2 systems lacking them (B1608+656 and B1600+434) to measure the mass in nearby or surrounding groups and clusters. ================================================================================ Proposal Category: GO Scientific Category: AGN/Quasars ID: 9376 Title: A Powerful Double Radio Source from a Spiral Galaxy PI: William C Keel PI Institution: University of Alabama We have identified a powerful double radio source whose host galaxy is clearly a disk system, and probably a spiral. This violates a very general pattern among radio-loud AGN, and understanding this object may thus shed light on the differences among expressions of nuclear activity between spiral and elliptical hosts. We propose a set of images to verify the spiral morphology, seek evidence of a nuclear ionization cone and jet/ISM interactions via narrow-band imaging, and search for optical synchrotron emission from the radio jet. These data would show whether indeed this (already strong) case indeed represents a spiral galaxy producing a powerful double source, what kind of spiral, and how both the nuclear and extended activity compare to those in typical elliptical host systems. ================================================================================ Proposal Category: GO Scientific Category: ISM and Circumstellar Matter ID: 9377 Title: NICMOS Imaging Polarimetry of Compact Proto-Planetary Nebula Dust Shells PI: Toshiya Ueta PI Institution: University of Illinois at Urbana-Champaign We propose to resolve the structure of 4 proto-planetary nebula (PPN) dust shells by means of imaging polarimetry using NICMOS. In our previous WFPC2 imaging surveys, these PPNs show a compact elliptical nebulosity (of radius 0arcs5 to 2") with a prominently visible central star. These PPNs appear to be members of a distinct class of PPNs, compared with bipolar nebulae in which an optically thick dust lane obscures the central star. Based on our previous mid-IR PPN survey, these PPNs are expected to host an optically thin, edge-on toroidal dust shell as evidence for the intrinsic axisymmetry of the PPN shells caused by an equatorially-enhanced mass loss during the asymptotic giant branch phase. These PPNs, however, are too compact to be fully resolved at mid-IR even with large ground-based telescopes because mid-IR images are diffraction-limited. The unique ability of imaging polarimetry at unprecedented high resolution makes HST the only instrument capable of isolating dust-scattered, polarized light from the shell and directly resolving the structure of compact PPNs without being hindered by the dominantly bright central star. These observations and following analysis with our radiative transfer code will provide crucial clues to the physical mechanism that drives the axisymmetric mass loss from originally spherically symmetric stars, which still remains to be one of the fundamental problems in astrophysics. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9378 Title: Galaxy Dynamics at Very Large Radius using LyAlpha Absorption Lines PI: Stephanie Cote PI Institution: Herzberg Institute of Astrophysics, NRC We propose to investigate the outer dynamics of the nearby spiral galaxy NGC1398 at very large galactocentric radii by using the kinematical information from Ly-alpha absorption lines in the spectra of 3 background UV- bright objects (two Seyferts 1 and one QSO). It is a unique opportunity to have 3 UV-bright objects surrounding one single isolated spiral galaxy, and this will enable us to measure its disk rotation up to radii several times greater than what is possible in HI at 21cm, since the UV-bright objects lie at projected distances of ~ 80 to 270 kpc. At these large radii we expect to observe the turn down from flat rotation, and be able to determine the size of the dark matter halo and hence measure the total mass and mass-to-light ratio of a spiral galaxy. ================================================================================ Proposal Category: SNAP Scientific Category: AGN/Quasars ID: 9379 Title: Near Ultraviolet Imaging of Seyfert Galaxies: Understanding the Starburst-AGN Connection PI: Henrique Schmitt PI Institution: National Radio Astronomy Observatory We propose a near-UV snapshot survey of 101 Seyfert galaxies using ACS/HRC and the filter F330W, a configuration which is optimal to detect faint star forming regions around their nuclei. These images will complement optical and near-IR images available in the HST archive, thus providing a panchromatic atlas of the inner regions of active galaxies, which we will use to study the starburst-AGN connection. The main goals of this proposal are: (1) Determine the frequency of circumnuclear starbursts in Seyferts, down to levels which cannot be observed from the ground; (2) characterize the observational (fluxes, colors, structure, sizes) and intrinsic (luminosities, masses, ages, global star-formation rate) properties of these clusters; (3) derive the luminosity functions of young star clusters around the nucleus of Seyferts and compare these results with those from normal and starburst galaxies to determine their survival rate close to the AGN; (4) address questions about the relation between AGNs and starbursts, like the possible connection between the masses and luminosities of black holes and starbursts, and the implications for the evolution of the black holes and their host galaxy bulges. By adding UV images to the existing optical and near-IR ones, this project will create an extremely valuable database for astronomers with a broad range of scientific interests, from the properties of the AGN to the properties of their host galaxies. ================================================================================ Proposal Category: GO Scientific Category: Cosmology ID: 9380 Title: Determination of Extragalactic Extinction Laws at UV wavelengths with gravitationally-lensed QSOs PI: Evencio Mediavilla PI Institution: Instituto de Astrofisica de Canarias The study of extragalactic extinction laws is of paramount importance as it plays a key role in galaxy evolution, as well as for the determination of the cosmological parameters, for example using SNe. We propose to utilize a new technique based on flux measurements of gravitationally lensed, multiply- imaged QSOs to estimate the extinction law of the lensing galaxy. Here we propose a pilot project of STIS observations of the doubly-imaged QSO SBS 0909+532 with a separation between images of 1.1 arcsec. Our goal would be to determine the extinction law at UV wavelengths in the lens galaxy (z=0.83). In a study that is the first of this type, we have obtained ground-based Integral Field Spectroscopy (IFS) data in the region of the 2175Angstrom PAH bump for SBS 0909+532. Our proposed observations will allow us to complete and extend the extinction law farther in the UV. Such observations would be impossible from the ground because they extend too far into the UV, and HST is the only instrument available with the necessary spatial resolution and sensitivity. ================================================================================ Proposal Category: GO Scientific Category: Stellar Populations ID: 9381 Title: The Birth of a Dwarf Galaxy: The Star Formation History of the Tidal Arm near NGC 3077. PI: Fabian Walter PI Institution: California Institute of Technology The extended tidal arm of neutral gas near NGC 3077 (member of the M 81 triplet, D~3.8 Mpc) is one of the most dramatic features of its kind seen in the local universe; it was created by an interaction with M 81 some 3*10^8 yr ago. It is one of the few tidal systems where atomic (HI) and molecular (CO) gas as well as low--level star formation (HAlpha) is detected over an area of several kpc^2. This tidal complex is believed to be in the process of forming a tidal dwarf galaxy. Using the unique resolving capability of the Hubble Space Telescope (HST) and the wide--field imaging capabilities of the ACS, we propose to perform a stellar population study of this tidally created system. By combining various methods to recover the star formation history (e.g., using the luminosity function of the core Helium burning stars) we will 1) measure the SF history since closest encounter with M 81, 2) determine whether older stars are present in the tidal feature or not and 3) investigate propagation of star formation across the tidal feature. This can be done with F435W, F555W, and F814W imaging using HST's ACS with only 8 orbits. We will, for the first time, recover the star formation history and the distribution of stars within a tidally created system. This study will also shed light on the creation and evolution of other tidal dwarf galaxies which are typically much further away. ================================================================================ Proposal Category: GO Scientific Category: Quasar Absorption Lines and IGM ID: 9382 Title: A Large Targeted Survey for z < 1.6 Damped Lyman Alpha Lines in SDSS QSO MgII-FeII Systems PI: Sandhya Rao PI Institution: University of Pittsburgh We have searched the first public release of SDSS QSO spectra for low-z (z < 1.65) metal absorption lines and found over 200 large rest equivalent width MgII-FeII systems. Previously, we empirically showed that such systems are good tracers of large neutral gas columns, with ~50% being classical damped Lyman alpha (DLA) systems (N2 * 10^20 cm^-2). Here we propose to follow up a well-defined subset of 79 of them to search for DLAs with 0.47 < z < 1.60. Only QSOs brighter than 19 were selected. The QSO emission and DLA absorption redshifts were constrained to virtually eliminate data loss due to intervening Lyman limit absorption. Consequently, we expect to discover ~40 new DLAs, which is a three-fold increase in this redshift interval. This will significantly improve our earlier low-z DLA statistical results on their incidence, cosmological mass density, and N2 distribution. The results will also allow us to better quantify the empirical DLA -- metal-line correlation. With this improved understanding, the need for follow-up UV spectroscopy will lessen and, with the release of the final database of SDSS QSO spectra (an ~25-fold increase), the number of low-z DLAs could be increased arbitrarily. Thus, the power of the large and statistically-sound SDSS database in combination with a proven technique for finding low-z DLAs will, over the next few years, essentially solve the problem of making an accurate determination of the cosmic evolution of the neutral gas component down to z ~0.4. ================================================================================ Proposal Category: GO Scientific Category: ISM and Circumstellar Matter ID: 9383 Title: Probing the Grains Responsible for Extinction Using Small Magellanic Cloud Sightlines PI: Karl Gordon PI Institution: University of Arizona Small Magellanic Cloud sightlines have the greatest potential to relate specific interstellar extinction features to distinct grain properties. The reasons for this are 1) prominent extinction features such as the 2175 Angstrom bump and the far-ultraviolet rise vary among SMC targets and 2) grain types may be very different from those in the Galaxy. Specifically, Welty et al. (2001) recently identified an SMC sightline that contains dust, but no silicate grains. Silicates are a dominant source of extinction in all dust models; the SMC may be the only location where the importance of silicates can be verified or disproven. We propose to explore the relationship between grain types and extinction toward 2 SMC stars with very different extinction curves; AzV 18 lacks a 2175 Angstrom bump and has a strong far-UV rise while the extinction curve towards the SMC star AzV 456 has a prominent 2175 Angstrom bump and a much weaker far-UV rise. We will compare the interstellar abundances of atoms that are prevalent in silicates (Si, Mg, Fe) toward these 2 stars and use the results to constrain dust extinction models. These SMC observations, which can only be obtained with STIS, are the only direct way to probe the connection between grain types/environments and extinction. The results from this study will be useful for modeling and understanding all regions that contain dust (AGN, circumstellar disks, star formation regions, etc.). ================================================================================ Proposal Category: GO Scientific Category: Solar System ID: 9384 Title: Ozone, Condensates, and Dust in the Martian Atmosphere PI: Philip James PI Institution: University of Toledo We propose to utilize the unique UV capabilities of STIS and ACS/HRC in order to study the spatial and seasonal variations in ozone, condensates, and dust in the Martian atmosphere. The data obtained will be critical in addressing recent breakthroughs in understanding the basic radiative, transport, and microphysical processes that provide for both long-term and short-term balance within the global Mars climate system. The proposal includes both Cycle 11 & 12 observations in order to span the classic dust storm season on Mars and provide the first good opportunity for HST to synoptically observe a dusty atmosphere on the planet. The UV observations will complement broad- band visible and IR observations that will be made during the Mars Global Surveyor Extended Mission and will provide support for the future UV observations of MARCI on the 2005 Mars Reconnaissance Orbiter. ================================================================================ Proposal Category: GO Scientific Category: Solar System ID: 9385 Title: Spatially-resolved polarimetry of Titan PI: Mark Lemmon PI Institution: Texas A&M University Titan's stratospheric haze not only hides the surface in visible light, it also traces the progress of Titan's seasons and controls the solar flux into the troposphere. Since 1994, we have monitored the seasonal context on Titan. We propose to continue this program and, with ACS and NICMOS, we can add important new measurements. Spacecraft polarimetry has suggested small particles, while high phase angle images suggest larger particles. Two types of models have been used to successfully explain the discrepancy: larger particles held above smaller particles by Titan's atmospheric dynamics; or a more uniform distribution of fluffy aggregate aerosols. The distinction is not just a question of large particles vs. small, it is about the process that governs the evolution of Titan's haze. New constraints have been slow in coming. Titan's disk integrated polarization near zero-phase angle does not distinguish the models. Intensity alone does not distinguish the models. We have the opportunity to make a set of observations that can test the models. We propose to obtain disk-resolved polarization measurements from 0.2 to 2 micron. We will use this information to develop a set of constraints on the type of particles in Titan's stratosphere. We will also continue our program of monitoring seasonal change on Titan, and use the data sets to provide context to the Cassini mission. ================================================================================ Proposal Category: SNAP Scientific Category: Solar System ID: 9386 Title: Infrared Photometry of a Statistically Significant Sample of KBOs PI: Keith Noll PI Institution: Space Telescope Science Institute While the discovery rate of Kuiper Belt objects is accelerating, the physical study of this new region of the solar system has been slowed by a lack of basic astrophysical data. Photometric observations of the majority of the more than 400 known KBOs and Centaurs are rudimentary and incomplete, particularly in the infrared. The multicolor optical-infrared photometry that exists for a small subset of KBOs often shows significant discrepancies between observations by different observers. Their intrinsic faintness puts them at the practical limits of ground-based systems. In July 2001 we began what will be the largest uniform sample of optical photometry of KBOs with a WFPC2 SNAPSHOT program that will perform accurate photometry at V, R, and I on a sample of up to 150 targets. We seek to greatly enhance the value of this survey by obtaining J and H photometry on the same sample using NICMOS. Combined optical and infrared broad band photometry is a far more powerful tool for physical studies than is either alone. Our sample includes objects that will be observed at thermal infrared wavelengths by SIRTF and will be used with those data to derive the first accurate diameters, albedos, and surface properties for a large sample of KBOs. ================================================================================ Proposal Category: GO Scientific Category: AGN/Quasars ID: 9387 Title: The Natural Occulting Disk and Host Galaxy of the Red BAL Quasar FIRST J1556+3517 PI: Michael Brotherton PI Institution: NOAO We propose an innovative imaging observation of the host galaxy of the red, broad absorption line (BAL) quasar FIRST J1556+3517. This object is already noteworthy as being the first radio-loud BAL quasar, and moreover a member of the very rare class of "Fe-LoBAL" quasars. FIRST J1556+3517 also has the unique property (out of some 60+ BALQSOs) of having unpolarized BAL troughs wider than the bandpass of the linear ramp filter of ACS. This unpolarized trough light most likely arises from stars comprising the host galaxy of FIRST J1556+3517. In this special quasar exists a natural occulting disk -- the BAL outflow -- and the opportunity to image a quasar host galaxy at high redshift without the complications of separating out the quasar. Red low-ionization BAL quasars like FIRST J1556+3517 have been hypothesized to be young merger products with high accretion rates and active star formation, perhaps representing a key evolutionary state in the lifetime of massive galaxies. ================================================================================ Proposal Category: SNAP Scientific Category: Solar System ID: 9391 Title: High-Resolution Imaging of Pluto's Surface PI: Marc W. Buie PI Institution: Lowell Observatory We propose a series of SNAPSHOT observations with the ACS/HRC from which we will derive a two-color global map of Pluto's surface. We will image Pluto at F435W and F555W, wavelengths that have been extensively studied from the ground over the past 50 years. The maps will provide albedoes with accurate error determinations down to 52degrees South latitude. These observations will provide a second epoch of HST mapping of the active surface of Pluto as it continues to receed from the Sun and will provide an important context for other detailed studies of Pluto. These observations take advantage of the observational and scheduling constraints imposed on SNAPSHOT observations to collect an extremely high-quality dataset from which to construct surface maps. This proposal has an associated INNOVATIVE proposal component that will map Pluto at longer wavelengths using super-resolution techniques to provide constraints on the methane frost distribution. The combination of albedo maps (from this program) and methane maps (from the INNOVATIVE program) will provide the strongest observational constraints yet on the complex problem of volatile frost transport on Pluto. ================================================================================ Proposal Category: GO Scientific Category: Stellar Populations ID: 9392 Title: The Ancient Stars of M32 PI: Mario Mateo PI Institution: University of Michigan The question of whether the dwarf elliptical galaxy M32 contains a population of truly ancient stars has remained unsettled for decades. We recently used HST/WFPC2 to identify for the first time a population of RR Lyr stars in this galaxy. Since these stars are known only to be present in stellar populations older than 8-10 Gyr, we contend that M32 does possess an old stellar component and certainly cannot be comprised of only intermediate-age (~ 5 Gyr) stars as has been frequently suggested in the literature. Our earlier observations were insufficient to determine even the most basic photometric properties of these stars. Nor could we use the data to identify independent evidence of the old population that could help constrain just what fraction of the galaxy's stars are ancient. We propose new HST/ACS observations to (a) get periods and luminosities of the previously observed RR Lyr stars, (b) search for additional RR Lyr stars in a significantly larger volume of M32, and (c) obtain ultra-deep 2-color photometry to study the ancient main- sequence turnoff region of that galaxy directly, (d) look for radial population gradients in M32, both among the RR Lyr/Horizontal Branch and main- sequence populations, (e) compare the M31/M32 old populations in terms of metallicity spread, and (f) use the RR Lyr stars to precisely determine the relative and possibly the absolute distances of M32 and M31's halo. ================================================================================ Proposal Category: GO Scientific Category: Solar System ID: 9393 Title: Dynamics and Cloud Structure of Neptune PI: Lawrence Sromovsky PI Institution: University of Wisconsin-Madison A 4-year gap in detailed observation of one of the most active planets in our solar system can be ended by our proposed multispectral WFPC2 imaging of Neptune over a period of 4.5 Neptune rotations. Our objectives are (1) mapping the two-dimensional distribution of Neptune's discrete cloud features and zonal bands with sufficiently dense longitudinal sampling to insure detection of any Great Dark Spot, or other major storm system, up to 35degrees N, (2) characterizing Neptune's circulation by tracking cloud motions during two densely sampled half-rotations that ensure reliable target identification, (3) measuring cloud evolution and more accurate tracking of non-evolving features by sparse imaging at earlier and later rotations relative to the two densely sampled primary sequences, and (4) characterizing the vertical structure of clouds by imaging with filters that select varying amounts of Rayleigh scattering and methane absorption and by capturing their center-to-limb variations during intensely sampled feature transits. To enhance the characterization of cloud structure we will also propose coordinated groundbased IRTF and Keck observations, both using adaptive optics at near IR wavelengths that provide access to additional strong methane and hydrogen absorption bands. The proposed HST observations use the same filters as in 1996 and 1998, as well as additional filters, permitting detailed comparisons with previous observations. ================================================================================ Proposal Category: GO Scientific Category: Stellar Populations ID: 9394 Title: Halo Microlensing: Direct Detection of a Microlens PI: Kem Cook PI Institution: Lawrence Livermore National Lab The MACHO project has recently released 5.7 years of LMC microlensing data, presenting 17 candidate microlensing events. These events suggest an 8-50 MACHO halo and a most likely MACHO mass of 0.2-0.9 M. However, nearly a decade after the first reported event (Alcock et al. 1993) there still remains much debate about the nature and location of the lensing matter. MACHO has also obtained WFPC2 follow-up data of the microlensing source stars, to date we have observed 16 candidates with HST. The WFPC2 follow-up data of MACHO event LMC-5 provided unexpected insight into the nature of the lens. This image revealed a very red, faint object displaced by 0.134^ from the source star which may well be the first direct detection of the dark matter component (lens) of a microlensing event. A second epoch of WFPC2 photometry will verify the proper motion of the lens and allow for a parallax measurement of its distance. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9395 Title: Is Bulge Formation Still Going-On? , An ACS Survey of Pseudo-Bulges PI: C. Marcella Carollo PI Institution: Columbia University vspace*-0.2truecm Pseudo-bulges, i.e., bulges with an exponential light profile, have been unveiled in the centers of many intermediate-type disks. Their structural similarity with the disks provides support to theoretical scenarios in which bulges may form due to secular evolution processes within the host disks. If at play, these processes would likely be active throughout a large fraction of cosmic history down to our days: `young' bulges should exist ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9396 Title: Young Cluster Systems in Two Super-Gas-Rich , Mergers: Arp 220 and Arp 299 PI: Christine Wilson PI Institution: McMaster University Massive young star clusters are found in large numbers within the mergers of massive, gas-rich disk galaxies. The most outstanding and well studied case is in the nearby merging Antennae pair (Whitmore and colleagues). These systems may give us our best hope to see directly the way in which globular clusters formed in the uniquely gas-rich protogalactic era of the universe. But, even in the Antennae, the many hundreds of young clusters have a median mass which is still 5 to 10 times smaller than the characteristic mass ~ 3 * 10^5 M that characterizes normal, old-halo globular clusters. To find objects closer to the mass range of "true" protoglobular clusters, we need mergers which are still more gas-rich than the Antennae and in which the gas has been collected into more massive GMCs. Two excellent candidates are Arp 220 and Arp 299, both of which are undergoing extremely high star formation rates and have > 10^10 M of molecular hydrogen compressed into their central few kpc. With the ACS High Resolution Camera we will obtain deep UBVI imaging of the active central regions of these galaxies, allowing us to trace the luminosities, colors, masses, and ages of the young star clusters within them. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9397 Title: Unmasking the optical counterpart to the ultraluminous X- ray source, NGC 5204 X-1 PI: Timothy Roberts PI Institution: University of Leicester We propose HST/STIS near- and far-UV spectroscopy of the recently identified optical counterpart to the ultraluminous X-ray source (ULX) NGC 5204 X-1 (Roberts et al. 2001). This source has since been resolved with HST/WFPC2 (data just public) into two sources with V magnitudes of 20.5 and 22.0 respectively, separated by 0.4 arcsecs (10 pc at the distance of NGC 5204). Existing low resolution ground-based data are dominated by the brighter source, the spectrum of which appears blue and apparently featureless, consistent with either (i) at least one unusually bright supergiant O star (M_v<=-7.8), or (ii) an O star association, although the data cannot presently rule out the presence of a background BL-Lac object. Ground-based data cannot unambiguously type both the new sources, due to their small separation (there are no bright nearby stars necessary for adaptive optics), and the absence of strong features in the optical spectra of O stars. By observing with the HST/STIS far- and near-UV MAMA we will obtain spectra in a waveband rich in O star absorption features, with sufficient S/N (10--15) and resolution (0.6-1.5Angstrom) to identify the sources, and reveal the nature of the first optical counterpart to an ULX. This result will be an important step in determining whether most ULX systems contain a new, 10^2 - 10^3 M `intermediate-mass' class of black hole. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9398 Title: Understanding Irradiation and Dipping Behaviour in Low Mass X-ray Binaries PI: Robert Hynes PI Institution: University of Southampton It is now clear that X-ray irradiation is the driving force behind many of the observed properties of accretion discs on a huge range of scales from Galactic interacting binaries to AGN. However to study the detailed physics of this process requires the accessible timescales and geometrical constraints afforded by Galactic low mass X-ray binaries (LMXBs). The ideal object for this study is EXO 0748--676 (UY Vol) because of its high inclination and full spectrum of LMXB phenomenology: type I bursts, dips and total eclipses. It is also remarkable as it was designated a transient on its discovery in 1985, but remains X-ray active to this day, thereby providing a potential unifying link between persistent and transient systems. Its present high state is likely maintained by X-ray heating; hence we can learn about a disk strongly influenced by irradiation. STIS TIMETAG observations in the far-UV will eclipse map continuum and emission lines; examine obscuration by the likely thick disk rim; and search for the UV signatures of dips and bursts. This provides an unprecedented range of techniques with which to probe the structure of an irradiated accretion disk and further our understanding of the irradiation of accretion flows in general. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9399 Title: Insights into Elliptical Galaxy Formation from HST Imaging of Shell Galaxies PI: David Carter PI Institution: Liverpool John Moores University We propose to use ACS to carry out an imaging survey of the cores of shell galaxies. Key to understanding several aspects of shell formation is to determine how far in do shells exist. Photometric detection from the ground is limited by seeing and sampling to radii of at best R ~ 10 - 15 arcsec. In velocity maps derived from high spatial resolution long-slit and integral- field ground-based spectra we have found shell-like features with distinct kinematics in several shell galaxy cores (R ~ 3 - 5 arcsec ~ 1 kpc). Hence we believe that shells may extend further in than previously known. HST provides the spatial resolution and sampling needed to map out shells in the pronounced surface brightness gradients of elliptical galaxy cores. The data will allow us to detect and map inner shells, to measure their colors, to establish their dynamics with the help of ground-based kinematics, to compare the inner surface brightness profiles of shell and non-shell ellipticals, and to measure the mass and distribution of the dust. Where shells are found, combined spatial and velocity information will establish the orbital structure of shell-producing merger debris on the basis of data, and will allow useful checks of the models for formation of shell systems in early-type galaxies. ================================================================================ Proposal Category: GO Scientific Category: Stellar Populations ID: 9400 Title: Are there young galaxies in the local universe: the age of the blue compact dwarf galaxy I Zw 18 PI: Trinh Xuan Thuan PI Institution: Astronomy Department, University of Virginia The question of whether there exists young galaxies in the local universe is important for cosmology. Cold Dark matter models predict that low-mass galaxies could still be forming at the present epoch. In the hierarchical model of galaxy formation, large galaxies result from the merging of smaller structures. These primordial building-block galaxies are too faint and small to be studied at high redshifts, while we stand a much better chance of understanding them if we can find some local examples. One of the best candidates for being a young nearby galaxy forming stars for the first time at the present epoch, is the blue compact dwarf (BCD) galaxy I Zw 18 because of its extremely low heavy element content (2 We propose to obtain deep V and I ACS images of I Zw 18. Our goal is to detect or put limits on the red giant branch (RGB) stellar population in this galaxy. If RGB stars are not detected, then we can set an upper limit for the age of I Zw 18 to be less than ~ 1 Gyr. If they are detected, I Zw 18 is not young, and the RGB tip can be used to derive its distance and set limits on the metallicity of the pregalactic gas. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9401 Title: The ACS Virgo Cluster Survey PI: Patrick Cote PI Institution: Rutgers, The State University of New Jersey We propose the most comprehensive imaging survey to date of low-redshift, early-type galaxies. Our goal is to exploit the exceptional imaging capabilities of the ACS by acquiring deep images --- in the SDSS g^ and z^ bandpasses --- for 163 E, S0, dE, dE,N and dS0 galaxies in Virgo, the nearest rich cluster. This extraordinary dataset would likely constitute one of the principal legacies of HST, and would have widespread applications for many diverse areas of astrophysics. Our immediate scientific objectives are threefold: (1) measure metallicities, ages and radii for the many thousands of globular clusters (GCs) in these galaxies, and use this information to derive the protogalactic mass spectrum of each galaxy; (2) measure the central luminosity and color profile of each galaxy, and use this information to carry out a completely independent test of the merging hierarchy inferred from the GCs, with the aid of N-body codes that simulate the merger of galaxies containing massive black holes; and (3) calibrate the z^ -band SBF method, measure Virgo's 3-D structure, and carry out the definitive study of the GC luminosity function's precision as a standard candle. Our proposed Virgo Cluster Survey will yield a database of unprecedented depth, precision and uniformity, and will enable us to study the record of galaxy and cluster formation in a level of detail which will never be possible with more distant systems. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9402 Title: A NICMOS Study of Merging Nuclei in the Toomre Sequence: Finding Order Amid Chaos PI: Seppo Laine PI Institution: Space Telescope Science Institute The final death throes of merging spiral galaxy nuclei are hidden behind dusty maelstroms of colliding gas clouds and glaring star formation activity. The dynamically important centers of mass can only be uncovered by imaging at NIR wavelengths and with the high spatial resolution of HST. We propose a near- infrared imaging program to inspect the physical processes of merging at spatial scales of ~100 pc. The Toomre Sequence provides the best sample of merging galaxies for such a study, because it has been studied extensively from the ground, and the global properties are well understood. Our previous Cycle 9 WFPC2 images of the nuclei have revealed a wealth of information on star forming activity and dust, but based on those data alone it is impossible to determine the locations of the current centers of mass. Determining the mass centers and stellar density profiles is important for understanding both the kinematics and the dynamical evolution of the nuclei, and the formation of nuclear density cusps in galaxies. We propose J, H and K band imaging of the nuclei in early and intermediate stage mergers in the Toomre Sequence. Because of the much reduced effect of dust extinction, the near-infrared images are also optimally suited to searches for nuclear rings and bars around the nuclei. Combined with our ongoing Cycle 9 program, these data will provide a detailed view of the structure and evolution of a sequence of merger nuclei. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9403 Title: Galaxy Formation in Nearby Voids: Reflections of the High-Redshift Universe? PI: Norman Grogin PI Institution: Space Telescope Science Institute vspace-.075inGalaxy voids, at the opposite environmental extreme from galaxy clusters, present an ideal yet under-utilized laboratory for probing the relationship between environment and the mechanisms of galaxy formation and evolution. Mounting evidence from ground-based surveys of galaxies in voids suggests that they have formed comparatively recently (and many are still forming) from gas-rich, low velocity-dispersion surroundings: a picture in accordance with models of hierarchical structure formation. The superior resolution of HST allows us to verify this hypothesis with the first directed HST imaging survey of void galaxies (VGs). With HST/ACS deep imaging of a subset of E+S0 VGs from our earlier ground-based imaging and spectroscopic survey, we will investigate their globular cluster (GC) systems to unravel their formation history and to constrain the age of their oldest GCs. The HST resolution of their inner light profiles will reveal whether they have significantly under-massive central black holes, as might be expected if these are young systems. HST will also detect the presence of morphological fine structure indicative of recent merger activity. If the present-day VGs truly reflect the early stages of galaxy formation which occurred at higher redshift outside the voids, their proximity enables the investigation of galaxy formation processes in much greater detail than possible from observations of the high-redshift field, even with NGST. ================================================================================ Proposal Category: GO Scientific Category: Cosmology ID: 9404 Title: Spatially Resolved Stellar Populations in Two z~2.5 Gravitational Arcs PI: David Thompson PI Institution: California Institute of Technology We propose to use ACS and NICMOS to observe two gravitationally lensed galaxies at z~2.5. We will combine these data with existing archival and scheduled GTO observation to make spatially resolved maps of color, dust, and age for these objects. We will then use these maps to study the properties of individual star-forming regions within these galaxies, to search for an underlying old stellar population between the knots of active star formation, and to test previous HST and ground-based studies which have hitherto relied on spatially unresolved colors alone to study stellar population in high redshift star-forming galaxies. Ours will be the first study of stellar populations of Lyman Break Galaxies on sub-galactic scales, and will give important new insights into the way that these high-z galaxies are assembled. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9405 Title: The Origin of Gamma-Ray Bursts PI: Andrew Fruchter PI Institution: Space Telescope Science Institute The rapid and accurate localization of gamma-ray bursts (GRBs) promised by a working HETE-2 during the coming year may well revolutionize our ability to study these enigmatic, highly luminous transients. We propose a program of HST and Chandra observations to capitalize on this extraordinary opportunity. We will perform some of the most stringent tests yet of the standard model, in which GRBs represent collimated relativistic outflows from collapsing massive stars. NICMOS imaging and STIS CCD spectroscopy will detect broad atomic features of supernovae underlying GRB optical transients, at luminosities more than three times fainter than SN 1998bw. UV, optical, and X-ray spectroscopy will be used to study the local ISM around the GRB. Chandra spectroscopy will investigate whether the GRB X-ray lines are from metals freshly ripped from the stellar core by the GRB. HST and CTIO infra-red imaging of the GRBs and their hosts will be used to determine whether `dark' bursts are the product of unusually strong local extinction; imaging studies may for the first time locate the hosts of `short' GRBs. Our early polarimetry and late-time broadband imaging will further test physical models of the relativistic blast wave that produces the bright GRB afterglow, and will provide unique insight into the influence of the GRB environment on the afterglow. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9406 Title: GD 552: The Oldest Cataclysmic Variable PI: Joseph Patterson PI Institution: Department of Astronomy, Columbia University A terrible puzzle has long afflicted our understanding of the evolution of cataclysmic variables (CVs). Angular momentum loss should grind the binaries down to orbital periods near 1.3 hr in 2 -- 4 Gyr, and then slowly drive them apart again. Most CVs should therefore have undergone ``period bounce" long ago, and be evolving towards longer period, with secondaries << 0.1 M. However, not a single post-bounce CV has been conclusively identified. Where are the old CVs hiding? They should be hard to find since they're probably faint intrinsically, and because their accretion rates may be too low to trigger dwarf-nova eruptions. One, and only one, good candidate appears in the Lowell proper-motion lists. This is GD 552: noneruptive, possessing a light secondary, and probably the least luminous CV yet found (M_V >~ +12.5). An accurate FGS parallax will establish whether this object (clearly very nearby) signifies a large population of very old CVs. A 1200 -- 10000 Angstrom spectrum would likely represent a pure steady-state low-M disk (the only one known), and the FUV region would provide a measurement of T_ eff in a white dwarf long after eruptive heating episodes have stopped. The UV observation obviously requires HST, and efforts to measure the parallax from the ground are thwarted by a background star 0^ .7 distant. ================================================================================ Proposal Category: GO Scientific Category: Cool Stars ID: 9407 Title: FGS Astrometry of a Star Hosting an Extrasolar Planet: The Mass of Upsilon Andromedae d PI: G. Fritz Benedict PI Institution: University of Texas We propose observations with HST/FGS to determine the astrometric elements (perturbation orbit semimajor axis and inclination) produced by the outermost extra-solar planet orbiting the F8V star Upsilon Andromedae. These observations will permit us to determine the actual mass of the planet by providing the presently unknown sin i factor intrinsic to the radial velocity method which discovered this object. An inclination, i = 30degrees, within the range of one very low precision determination using reanalyzed HIPPARCOS intermediate data products, would produce the observed radial velocity amplitude, K = 66 ms with a companion mass of ~8 M_Jupiter. Such a mass would induce in Upsilon Andromedae a perturbation semi-major axis, Alpha = 0arcs0012, easily within the reach of HST/FGS fringe tracking astrometry. The proposed observations will yield a planetary mass, rather than, as previous investigations have done, only suggest a planetary mass companion. ================================================================================ Proposal Category: GO Scientific Category: Cool Stars ID: 9408 Title: Calibrating the Mass-Luminosity Relation at the End of the Main Sequence PI: Todd Henry PI Institution: Georgia State University 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 0.05 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 interferometry 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 equaled 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. Three of the targets are brown dwarf candidates, including the current low mass record holder, GJ 1245C, with a mass of 0.062 +/- 0.004 Msun. The payoff of this proposal is high because all 10 of the systems selected have already been resolved with HST-FGS3/FGS1R during Cycles 5--10 and contain most of the reddest objects for which masses can be determined. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9409 Title: The Evolution of Globular Cluster Systems in Merger Remnants PI: Paul Goudfrooij PI Institution: Space Telescope Science Insititute Mergers seem to have played a major role in determining the shapes and dynamics of elliptical galaxies. A few galactic mergers still occur and offer valuable clues to past evolutionary processes. Globular clusters formed during mergers are crucial probes for age-dating such events, and help shed light on the process of cluster formation and evolution. With young globulars in ongoing mergers now well studied, we propose to make deep ACS observations of intermediate-age globular clusters in three bona fide ellipticals: NGC 1316, 1700, and 3610. These ellipticals all have line-strength indices, UBV colors, and fine structure indicative of their being 2 -- 4 Gyr old merger remnants. Past HST+WFPC2 observations have shown that they also possess significant numbers of intermediate-age globulars as part of their bimodal cluster populations. We plan to use the new HST+ACS observations to (1) measure high-accuracy BVI colors for clusters up to ~ 2 -- 3 mag fainter than ever before, (2) use these colors to separate first- and second-generation clusters, and (3) determine the luminosity functions of the two kinds of clusters to 3 -- 4 mag past the peak for old globulars. Deep dithered BVI images form a crucial part of our observing strategy. This program should permit---for the first time---to directly detect the predicted evolution of the cluster luminosity function from a power law for young clusters to the Gaussian distribution typical of old globulars. ================================================================================ Proposal Category: GO Scientific Category: ISM and Circumstellar Matter ID: 9410 Title: The Galactic Warm Ionized Medium: the First Direct Measures of its Ionization and Abundances PI: J. Christopher Howk PI Institution: The Johns Hopkins University The warm ionized medium (WIM) is the dominant gaseous component of the Galactic halo and represents an important sink of the radiative and kinetic energy output of stars and supernovae, though the source of its ionization remains unknown. We will use STIS spectroscopy of the post-AGB stars ROB 162 and ZNG 1 in the globular clusters NGC 6397 and Messier 5 to measure directly the abundances and ionization states of several key metals in the Galactic WIM. These sight lines are unique: because the two clusters also contain pulsars with published radio dispersion measurements, these are the only sight lines for which we can derive the column densities of both HI,em and ionH2, as well as the columns of multiple ionization stages of the important metals S, P, and Fe. We will use the proposed STIS observations with existing FUSE data to derive the total gas-phase abundances of S, P, and Fe for the material along these sight lines with no ionization uncertainties. We will directly measure the ionization fractions of S and P in the WIM. We will also infer the dust content of the WIM. Our study of the ionization state and dust content of the WIM will provide the best yet constraints for models of this gas. Our work will also provide the best constraint for the fundamental "cosmic" reference abundance (averaged over these sight lines) of the undepleted elements S and P. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9411 Title: Morphologies and faint neighbors of z=4.5 Lyman Alpha Emitting Galaxies PI: Sangeeta Malhotra PI Institution: The Johns Hopkins University We propose to image one ACS field containing four spectroscopically confirmed Ly-alpha emitters at z=4.5 in restframe UV and a narrowband filter containing the Ly-alpha line. These observations will (A) Reveal the morphology of the four spectroscopically confirmed sources. The high equivalent widths of the Ly-alpha line in these four galaxies in particular and this population in general cannot be explained without invoking one or more of: extreme youth of the stellar population, zero metallicity, energetic winds or type II quasars. Comparison of morphologies in the line and continuum would help favor or rule out some of these possibilties. This would also tell us whether the star- formation is uniformly distributed or centrally concentrated or concentrated but in many clumps? Proximity of these galaxies (average projected physical separation of 200 kpc, with one pair 30 kpc apart) also makes interactions likely. (B) Extend the luminosity function of Ly-alpha sources by 2.5 magnitudes due to better spatial resolution of HST and sensitivity of ACS. We will be able to detect sources with line flux of ~eq 2 * 10^-18 ergcm2s over 11.5 sq-arcmins (~ 100 sources). This complements the LALA (Large Area Lyman Alpha) survey which covers 1/3 square-degree to a line sensitivity of ~eq 2 * 10^-17. Thus we get a picture of this patch of young universe in two ways: statistics of faint galaxies and morphologies of relatively bright ones. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9412 Title: The Physical Parameters of the Hottest, Most Luminous Stars as a Function of Metallicity PI: Philip Massey PI Institution: Lowell Observatory We have obtained excellent, new ground-based blue optical and HAlpha spectra of a sample of very early-type stars in the Magellanic Clouds in order to measure their physical properties, for comparison with the extensive data that exists for higher-metallicity Galactic stars. Our aim is to understand how effective temperatures depend upon metallicity (necessary in determining IMFs), and to explore the astrophysically interesting regime of stars of extreme temperatures, masses, and luminosities. In order to do this, we need to measure the stellar wind terminal velocities for our stars, necessary to constrain the stellar models. These can only be measured with STIS/FUV on HST. In addition, we will obtain higher spatial resolution data on the HAlpha line for several stars for which nebular contamination is significant in our ground-based data. We also include several R136 stars with excellent STIS/CCD data but which lack UV line measures. These new HST data will provide important information about the strengths of stellar winds at extreme luminosities and the calibration of the Wind Momentum-Luminosity Relationship at lower metallicities. This proposal was highly rated in Cycle 9, but only 4 snapshots were obtained. We have completed the analysis of these plus additional data from the archives, but need spectra of the remaining objects if we are to answer the questions we pose. ================================================================================ Proposal Category: GO Scientific Category: AGN/Quasars ID: 9413 Title: Infrared Spectroscopy of z > 5 QSOs PI: Michael Corbin PI Institution: Space Telescope Science Institute The elemental abundances of high-redshift QSOs provide an important probe of the early universe. The ratio of iron to alpha-process elements observed in all QSOs to z ~ 4.5 in particular suggests that the gas has been enriched by Type Ia supernovae. Evidence of such enrichment in turn helps constrain the ages and masses of QSO host galaxies, which can be compared with the predictions of galaxy formation models under currently popular LambdaCDM cosmologies. With these motivations we propose to obtain NICMOS grism spectra of five bright (z^* ~ 19) QSOs from z = 5.03 to z = 6.28 recently discovered in the Sloan Digital Sky Survey. Our main goal will be to measure the strength of the broad Fe II emission complex at 2500 Angstrom (rest) in these very young (~ 1 Gyr) objects, if it is present at all. With the exception of two objects at z = 5.99 and z = 6.28 it will also be possible to measure the Mg II Lambda2800 line. These measurements are impossible from the ground because of the atmospheric absorption bands in the near infrared. The Fe II / Mg II emission ratio will in turn be used to estimate the relative abundance of these elements in the objects, and to compare these abundances to those of QSOs at lower redshifts. The infrared brightness of the objects and reduced sky background will allow high signal-to-noise ratio spectra to be obtained in relatively short integration times (1 orbit per object). ================================================================================ Proposal Category: GO Scientific Category: Stellar Populations ID: 9414 Title: Resolved halo stellar populations in the Milky Way analogue edge-on galaxy NGC 891 PI: Richard de Grijs PI Institution: University of Cambridge The stellar halo is one of the fundamental building blocks of galaxies. Although ground-based surface photometry has shown that stellar halos exist in some spiral galaxies, with colours similar to those of the main disk, little else is known about their stellar populations. We propose to carry out a systematic study of the halo regions of the edge-on galaxy NGC 891. The resulting deep colour-magnitude diagrams will be used to infer the mean metallicity of the bright halo giants at the tip of the RGB and below, and its metallicity spread. Recently, Zepf et al. (2000) inferred that the halo metallicity of NGC 5907 has to be low (Fe/H <=sssim -1.7), with a large stellar M/L ratio. We will be able to test this hypothesis with much better and deeper data. If we can confirm a similar halo composition in NGC 891, this would imply that the Milky Way halo might be very different from external halos. Since galactic halos trace the history of galaxy formation, this will have important implications for our understanding of galactic evolution on cosmological time scales. Using these survey data, we will be able to conclusively distinguish between genuine halo objects and merger remnants, without having to assume a scenario in which the halo field population is fully mixed. Surprisingly, such studies have not yet been undertaken for NGC 891, although the galaxy is a prime Milky Way analogue. ================================================================================ Proposal Category: GO Scientific Category: ISM and Circumstellar Matter ID: 9415 Title: Is the Compact HVC Toward Ton S210 Remnant Debris from the Formation of the Local Group? PI: Kenneth Sembach PI Institution: Space Telescope Science Institute There is a fortuitous coincidence in the positions of the quasar Ton S210 and a compact ionH1 high velocity cloud on the sky that makes it possible to test the hypothesis that such clouds are extragalactic entities located in the Local Group. The HVC toward Ton S210 has ionH1 21 cm emission properties similar to those of isolated compact HVCs suspected of being Local Group clouds. It has recently been detected in ionO6 absorption by FUSE, which suggests that either there is hot gas associated with the collapse of the cloud or that the HVC is interacting with a hot, tenuous Galactic halo or Local Group medium. We propose to observe the HVC in absorption against the smooth ultraviolet continuum of Ton S210 with HST/STIS. To answer the question posed in the proposal title, we will combine the STIS observation with extant FUSE and ionH1 21 cm data to determine the metallicity, elemental abundances, and ionization properties of the HVC. To date, such information has been difficult to obtain for all but a few HVCs, and this is the first time such an opportunity has been available for a compact HVC. The results of this study will bear directly upon the issues of the locations of compact HVCs, the ionization conditions of HVCs detected in ionO6 absorption, and the possible influence HVCs might have on the chemical evolution of galaxies. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9417 Title: New Clues to the Origin of the Extreme Helium Stars PI: David L. Lambert PI Institution: University of Texas at Austin The extreme helium stars (EHes) are H-poor supergiants whose origins are not yet understood despite thorough analyses of optical spectra. This proposal seeks STIS echelle spectra for 7 stars from which novel data on their chemical compositions will be obtained to pin down key abundances. First, even the EHe's initial metallicity is uncertain; certain abundance ratios - e.g., Ca/S, Ti/S, and Fe/S - imply alterations of surface abundances among elements from Na to Ni resulting from fractionation or diffusive separation, possibly the result of winnowing of dust grains from gas. The zinc abundance measurable only from UV spectra will be a powerful clue to the true metallicity because it is known not to be removed by such winnowing. Second, elements affected by the s-process, the last of the major nucleosynthetic processes for which surface abundances are unknown for EHes, will be studied. The new abundances will be used to probe the evolutionary origins of these peculiar stars by comparisons with theoretical scenarios involving a merger of white dwarfs or a final He-shell flash in a low mass white dwarf, and with observed abundances for R Coronae Borealis stars that would seem to be close relatives of the EHes. Spectrophotometric observations of EHes obtained with GO 8603 will give accurate estimates of effective temperature and surface gravity that will be used in our abundance determinations. ================================================================================ Proposal Category: GO Scientific Category: Quasar Absorption Lines and IGM ID: 9418 Title: The Sight-line toward PHL 1811: A Rare Chance to Probe a Lyman Limit System at Very Low Redshift PI: Edward Jenkins PI Institution: Princeton University Observatory The sight-line to an extraordinarily bright quasar, PHL 1811, penetrates four gas systems at z( abs) < z( em)=0.192. One of them is a Lyman limit system (LLS: N( H I)>10^17.5, cm^-2) at z( abs)=0.08088 which is especially well suited for a study of atomic abundances, local density, and ionization state. We propose to obtain a STIS E140M spectrum with moderately good S/N so that we can measure absorption features that will permit the determinations of overall metallicity of the system, its nucleosynthetic ratios Alpha/Fe and Alpha/N, the fractions and kinematics of ionized gas, and the amount of gas-phase element depletions caused by dust. The LLS should be close enough for us to identify an associated galaxy, but to be sure we do not miss one very close to the quasar in projection, we plan to supplement our spectrum with a short- exposure ACS HRC image of the quasar's immediate surroundings. ================================================================================ Proposal Category: GO Scientific Category: Stellar Populations ID: 9419 Title: The Complete IMF of a Massive Young Cluster PI: Jesus Maiz-Apellaniz PI Institution: Space Telescope Science Institute We propose to use the large improvement in sensitivity and wide-field resolution provided by ACS to obtain for the first time the complete ~ 0.1 M to ~ 100 M IMF of a single massive young cluster. We will obtain BVI + nebular deep (V ~ 27) WFC photometry of six cluster and one background pointings and we will use the auto-parallel capacity of ACS to simultaneously acquire deep NUV+U+V photometry of selected regions in the cluster. Special care has been taken to treat all the complications which arise in the reduction of data for the purpose of calculating the IMF of a young cluster. We have chosen as our object of study N11 in the LMC because it arguably provides the best combination of stellar mass range (> 40 O stars, with several O3 stars), spatial resolution (1 WFC pixel = 0.0125 pc), low extinction (E(B-V) ~ 0.1), crowding, background confusion, and nebular contamination in comparison to other Galactic and Local Group clusters. It also has the advantage of having two separate regions, one which has already stopped forming stars and another one which is still forming them, thus allowing us to search for differences in the IMF between those two cases. The ACS data will be complemented with IR ground-based observations obtained using Gemini South, for which we already have been awarded time. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9420 Title: Intensive Coverage of the Eta Carinae Event in 2003 PI: Kris Davidson PI Institution: University of Minnesota For a variety of reasons, HST can provide a very special and unique data set when Eta Car experiences its next spectroscopic event in mid-2003. Explaining the phenomenon is only part of the motivation. This star and its ejecta have unique characteristics that make them important for several branches of astrophysics; and when a spectroscopic event occurs, it's like varying the parameters in an experiment (or rather, set of experiments). The 2003 event will be the last chance in the forseeable future to obtain such a data set. Eta Carinae has extreme parameters; it is mysterious in surprisingly basic ways; and HST/STIS can gather useful data on it at a terrific rate. As we explain below, the proposed data set will be valuable in several independent ways: It will help solve a specific set of current problems, it will constitute a large and unique archival data base for both stellar and nebular astrophysics, and it will be well-suited for educational uses. ================================================================================ Proposal Category: GO Scientific Category: Cosmology ID: 9421 Title: UV Observations of Hubble Flow Type Ia Supernovae PI: Peter Nugent PI Institution: Lawrence Berkeley National Laboratory Two independent research groups have presented compelling evidence for an accelerating universe from the observation of high-redshift Type Ia supernovae (SNe Ia). These findings have such important ramifications for cosmology that every effort must be made to thoroughly test the calibrated standard candles on which they are based, improve upon our understanding of the underlying physics of the SN Ia explosion mechanism and attempt to constrain or determine their progenitors. Here we propose to obtain STIS UV spectra of five Hubble Flow SNe Ia. The spectra will be taken at weekly intervals over a range in time starting slightly before maximum light and extending to +30 days. These observations will accomplish the following three goals: (1) Calibration of the rest frame UV light curves of SNe Ia and an assessment of their potential use as distance indicators through UV light curve shape analyses. (2) Improvement in our understanding of the physics of SNe Ia, metallicity/evolutionary effects and correlations between peak brightness and UV spectral features. (3) Calibration of the SNe Ia previously observed by HST at high-redshift. For z > 0.8 SNe Ia discovered by the Supernova Cosmology Project, the High-Z Supernovae Search Team and future HST discovered SNe Ia (like SN 1997ff found in the HDF) this data is crucial for proper cross-filter K-corrections and calibration of the supernova photometry. ================================================================================ Proposal Category: GO Scientific Category: Cool Stars ID: 9422 Title: Masses of AGB stars PI: Kenneth Hinkle PI Institution: NOAO There are few AGB stars with known masses. We have undertaken a program to measure spectroscopic orbits for about 50 binary systems containing M giants and typically white dwarfs. These are all single lined systems so the spectroscopic orbit of the M giant results in a mass function, m_2^3sin^3i / (m_1 + m_2)^2, for the secondary. Under special conditions, it is possible to undertake a simple observation that allows a solution for the masses. By measuring the angular separation at the epoch of greatest elongation of a zero eccentricity, eclipsing system (i.e. a system with a known inclination) m_1+m_2 can be determined, hence allowing the masses to be solved. Parallaxes indicate that there are two systems that can be resolved using HST/ACS. We propose to carry out this observation. ================================================================================ Proposal Category: GO Scientific Category: AGN/Quasars ID: 9423 Title: NICMOS Observations of Transient Infrared Jets in the Galactic Microquasar GRS1915+105 PI: Stephen Eikenberry PI Institution: Cornell University We propose to use HST/NICMOS to make Target of Opportunity observations of the galactic microquasar GRS1915+105. This source possesses transient radio jets which exhibit apparent superluminal motions, and resolved infrared emission from these jets has been observed in GRS1915+105 (Sams, Eckart, and Sunyaev, 1996; Eikenberry and Fazio, 1996). Because the jet ejection events are correlated with X-ray outbursts, we will use observations of X-ray flares with the Rossi X-Ray Timing Explorer to trigger the HST observations. We will then monitor GRS1915+105 periodically with NICMOS, obtaining relative astrometry, photometry, polarimetry, and grism spectroscopy of the jets and the parent object. These observations will allow us to greatly increase our understanding of the jets' radiative mechanisms and physical conditions, and their evolution with time. We require the capabilities of HST and NICMOS due to the small angular separations between the jets and the parent object (increasing from ~ 0.1 to ~ 0.8 arcsec over the span of the TOO observations) and the high reddening towards GRS1915+105 (A_V ~ 30 mag). ================================================================================ Proposal Category: GO Scientific Category: Star Formation ID: 9424 Title: Externally Illuminated Circumstellar Material in the , Young Nebulous Cluster NGC 2024 PI: Karl Stapelfeldt PI Institution: Jet Propulsion Laboratory HST imaging of the Orion M42 H II region has revealed circumstellar emission and absorption regions ("proplyds") with sizes comparable to those expected for protoplanetary disks. Disk morphology is directly observed in a dozen cases; disk photoevaporation is now the working model to explain the ionized rims seen at more than 100 Trapezium cluster stars. Are the Trapezium circumstances unique? Different cluster ages, densities, and UV radiation fields may strongly affect proplyd characteristics. To address these questions, we have searched for proplyds in several other young nebulous clusters, and found that the embedded infrared cluster associated with the NGC 2024 H II region has a large group of strong proplyd candidates. Our WFPC2 images of the optically visible edge of the cluster have identified an HAlpha proplyd aligned toward a B0 star. Our VLA 3.6 cm maps show compact ionization regions coincident with 20 members of the infrared cluster - a result similar to the original VLA proplyd discovery in M42 by Churchwell (1987). These results strongly indicate that infrared emission line imaging of selected cluster members should reveal many objects similar to the those in M42. We propose NIC2 Paschen Alpha and continuum imaging of fourteen of the NGC 2024 compact VLA sources. Our goal is to resolve and characterize their circumstellar structures, and compare them with those seen in M42. ================================================================================ Proposal Category: GO Scientific Category: Cosmology ID: 9425 Title: The Great Observatories Origins Deep Survey: Imaging with ACS PI: Mauro Giavalisco PI Institution: Space Telescope Science Institute We propose a Treasury program of ACS imaging as part of the Great Observatories Origins Deep Survey (GOODS), covering 320(square)', or 32* the area of the two original WFPC2 HDFs, to within 0.5--0.8 mag of their depth in four ACS bands, BViz. The two GOODS fields, the Hubble Deep Field North and Chandra Deep Field South, are the premier deep survey areas from X--ray to radio wavelengths. ACS data will provide unique angular resolution, sensitivity, and wavelength coverage to close the gap between the deepest Chandra and SIRTF observations. Supported by extensive imaging and spectroscopy from the VLT, Keck, Subaru, NOAO, Gemini, VLA, JCMT, and other facilities, the combined GOODS data set will make it possible to map the evolution of the Hubble sequence with redshift, reconstruct the history of galaxy mass assembly, star formation and nuclear activity from the epoch of reionization to the present, trace the growth of density perturbations via cosmic shear, and, with properly phased z--band observations, detect ~ 12 Type Ia supernovae at 1.2100 km KBOs and hence not yet detected. In particular, we will determine whether the current absence of objects with perihelia beyond 50 AU is due to a truncation of the protoplanetary disk at some point in Solar System history, or just a failure to accrete D>150 km objects. ================================================================================ Proposal Category: SNAP Scientific Category: ISM and Circumstellar Matter ID: 9434 Title: A SNAPSHOT Survey of the Hot Interstellar Medium PI: James Lauroesch PI Institution: Northwestern University We propose to obtain SNAPSHOT STIS echelle observations of key tracers of hot interstellar gas (ionC4, ionN5, and ionSi4) for selected FUSE Team ionO6 survey targets with known UV fluxes. By taking advantage of the SNAPSHOT observing mode we will efficiently obtain a large number of spectra suitable for the study of the highly ionized hot component of the interstellar medium (ISM). Our goals are to explore the physical conditions in and distribution of such gas, as well as to explore the nature of the interfaces between the hot ISM and the other interstellar gas phases. Using inter--comparisons of the various ionic ratios for ionC4, ionN5, ionO6, and ionSi4, we will be able to discriminate between the various models for the production of the highly ionized gas in the Galactic ISM. The survey will also enable detailed studies of regions already known to contain hot gas through X-ray emission measurements (e.g., SNRs and radio loops). The proposed SNAPSHOT observations will extend our previous Cycle 9 survey (which was compromised by the STIS side 1 failure), and should roughly double the number of stars for which high quality STIS observations of the important hot gas tracers are available, enabling us to derive a truly global view of the hot ISM. ================================================================================ Proposal Category: GO Scientific Category: Star Formation ID: 9435 Title: Systematic Search for Rotation at the Base of Outflows from T Tauri Stars PI: Francesca Bacciotti PI Institution: Osservatorio Astrofisico di Arcetri We wish to search for rotation signatures in the initial portion (first 100 AU) of a sample of outflows emanating from T Tauri stars (TTSs). This project originates from our detection of systematic transverse radial velocity shifts in STIS spectra of the DG Tau jet (Bacciotti et al., 2001a). The shifts, observed in a region where the flow is already collimated, but has not yet manifestly interacted with its environment, are consistent with the predictions of magneto-centrifugal launching models, and may constitute the first observed indication for rotation in the initial portion of a jet flow. Rotation is a fundamental ingredient in star formation theories, thus we propose to confirm the above result by carrying out a systematic survey in similar flows. We plan to take for each jet a STIS spectrum in the 6300 -- 6800 Angstrom range, with the slit perpendicular to the flow direction and at a distance of about 0.3" from the source (i.e., in our targets, 40 -- 70 AU along the jet depending on inclination angle). Since the flows are resolved transversely with HST, the proposed slit orientation allows for the direct detection of systematic velocity shifts. Where found, we will check for consistency between the sense of rotation observed and that of the underlying disk through CO interferometric measurements. As a by-product, estimates of the excitation conditions across the flow (including ionization fraction) and of the mass outflow rates will be derived. ================================================================================ Proposal Category: GO Scientific Category: Galaxies ID: 9436 Title: Proper Motions of Bulge Stars at b=-6: The Shape of the Potential in the Central kpc of the Galaxy PI: Konrad Kuijken PI Institution: Kapteyn Institute We propose to measure proper motions in a bulge field at l,b=0,-6, near the globular cluster NGC 6558. Suitable first-epoch data exist (from 1997). These data will allow us to calculate the vertical potential gradient in the bulge region, and hence the flattening of the potential in the central regions of the potential - a crucial piece of information for deciding measuring the central density of the dark halo of the Galaxy. Central halo densities currently constitute one of the most discrepant predictions of structure formation theories. In addition, the proper motions will allow us to make a kinematic separation between bulge, disk and globular cluster stars. The resulting cleaned colour-magnitude diagrams allow the bulge main sequence turnoff to be viewed cleanly, and compared with lower-latitude regions. Thus age and metallicity gradients in the bulge can be measured. ================================================================================ Proposal Category: GO Scientific Category: Hot Stars ID: 9437 Title: Quantitative Constraints for Massive Star Evolution Models with Rotation PI: Kim Venn PI Institution: U.Minnesota, Macalester College Rotation is now recognized as an important physical component in understanding massive stars. Theory suggests that rotation affects the lifetimes, chemical yields, stellar evolution tracks, and the supernova and compact remnant properties (Heger & Langer 2000, Maeder & Meynet 2000). In a Cycle 7 program, we proved that rotational mixing occurs in massive main sequence stars (Venn et al. 2001). In this proposal, we want to quantitatively test model predictions and constrain the theory for a better understanding of massive star evolution. We are requesting HST STIS observations of the ionB3 2066 Angstrom resonance line of seven massive stars in three young clusters carefully selected from IUE analyses. These stars show traces of boron depletion, but without nitrogen enrichment; rotation is the only theory able to explain this abundance pattern. These new abundances will allow us to test rotating model predictions: that mixing strength increases with stellar age, mass, and rotation rate. They will also help to quantitatively constrain the rotational mixing efficiencies in massive stars. One very high S/N spectrum of a moderately boron-depleted star is also requested. We wish to measure its ^11B/^10B ratio, which is predicted to change as boron is depleted in the rotating models. This ratio will further confirm rotational effects and observationally constr