Cycle 9 Abstract Catalog (based on Phase I Submissions) Generated on: Wednesday January 05, 2000 Proposal Category: GO Scientific Category: COS ID: 8559 Title: The Role of Dark Matter in Cluster Formation and Galaxy Evolution PI: Richard Ellis PI Institution: California Institute of Technology The outer regions of massive clusters represent transitional areas of great cosmological importance where field galaxies encounter the steep potential wells of dark matter and baryonic hot gas. Little is known about either the dark matter profile at large radii or the morphological properties of infalling galaxies at those redshifts where strong evolution is observed in the cluster cores. The former is central to understanding the puzzling high baryonic fraction observed in cluster cores with clear implications for the mean mass density, Omega_o. Understanding the mass distribution on large scales will also help separate cosmological field galaxy evolution from that driven by the environment. To address these questions we propose a wide-field imaging survey of the rich cluster Cl0024+1654 (z=0.40) which takes advantage of an extensive galaxy redshift survey we have compiled. We have designed an efficient sampling strategy which will simultaneously track the gravitational shear to at least simeq5h_50^-1 Mpc using proven mass reconstruction techniques developed with ground and HST-based data and connect this dark matter profile with the radial dependence of star formation, dynamical and morphological properties of recently-arrived cluster members. ================================================================================ Proposal Category: GO Scientific Category: COS ID: 8560 Title: Large Scale Structure at z ~ 0.9 PI: Lori Lubin PI Institution: California Institute of Technology We are requesting deep, broad-band red WFPC2 images of three fields within a supercluster at z ~ 0.9 in order to study the morphological properties of galaxies within a high-redshift large scale structure. Because significant evolution has already been observed in galaxy populations at this redshift, these observations will provide a crucial link between the global properties of large scale structure and galaxy-scale physics. The target supercluster contains two clusters which have already been well-studied by the proposers with Keck and HST. CL1604+4304 and CL1604+4321 are typical of Abell richness class 1 to 3 clusters. They are separated by 4100 km s^-1 and by only 7 h_0.7^-1 Mpc. This system is one of only two superclusters that are known at z ~great 0.9. The proposed HST fields cover the outskirts of the two clusters, as well as the very central supercluster region. These data will be combined with previous HST observations of the cluster cores to generate a complete sample of distant galaxies in a nearly contiguous area corresponding to 1 Mpc * 10 Mpc. The HST imagery, combined with a Palomar/Keck program to obtain photometric and spectroscopic coverage of the same region, will allow us to quantify the morphology--density relation over a wide range of local environments and to study the relationship between galaxies, clusters, and their surrounding large scale structure in the high-redshift universe. ================================================================================ Proposal Category: GO Scientific Category: COS ID: 8561 Title: The Ionizing Flux from Star-Forming Galaxies PI: Matthew Malkan PI Institution: University of California Meaningful upper limits on the amount of ionizing radiation from galaxies in the current epoch have been obtained (by HUT) for only 3 galaxies. The contribution of normal galaxies to the cosmic UV background flux is even more uncertain at earlier times. We propose to determine the emission of normal, intermediate-redshift, star-forming galaxies in the FUV. If their average escaping ionizing flux is even 1/10 of their strong mid-UV flux, they are a comparable or even larger source of the background than AGN. Even a small contribution from the numerous normal galaxies has far-reaching implications for the strength, spectrum, and spatial homogeneity of the diffuse ionizing flux. This ionization controls the properties of the young IGM, from the Ly- alpha forest to protogalaxies. The STIS/FUV-MAMA imager can provide an extremely sensitive measurement of the pure Lyman-limit continuum from the brightest galaxies at 1.1 <= z <= 1.7. Our integrations will be deep enough to provide detections or highly significant (50Sigma) upper limits, for more than three times as many galaxies as have been previously published (and those were only at low redshift). If the average ratio of Lyman limit/mid-UV fluxes is even as small as a few percent, these proposed observations will underlinedetect it. ================================================================================ Proposal Category: GO Scientific Category: COS ID: 8562 Title: Probing the Large Scale Structure: Cosmic Shear observations with STIS PI: Peter Schneider PI Institution: Max-Planck-Institut f. Astrophysik The distortion of light bundles from distant galaxies probes the statistical properties of the intervening inhomogeneous (dark) matter distribution. Its tidal gravitational field distorts the observable image shapes thereby causing a coherent ellipticity pattern (Cosmic Shear). The statistical properties of this pattern reflect those of the large-scale matter distribution in the Universe. Cosmic Shear can therefore probe the LSS without any reference to the relation between dark and luminous matter. Owing to the small magnitude of this effect, a reliable measurement of Cosmic Shear requires superb imaging of very faint objects. From our detailed and successful preliminary work on existing parallel imaging data with STIS, we have demonstrated that STIS provides the required image quality for this program due to its good pixel sampling and its small PSF anisotropy. We propose an imaging Parallel Program for Cycle 9, similar to that carried out in Cycle7. We propose to dedicate one and two orbit parallel opportunities to imaging with the 50CCD `Clear' filter. By combining the results from these two programs, we expect to measure the Cosmic Shear on the STIS angular scale with high precision. Comparison with light tracing through very large N-body simulations will allow us to constrain the cosmological parameters and fix the normalization of the dark matter power spectrum with high accuracy. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8563 Title: Determining the Duplicity of Nearby T Dwarfs (Methane Brown Dwarfs) PI: J. Davy Kirkpatrick PI Institution: Infrared Processing and Analysis Center Knowing the binary fraction of T-type dwarfs (methane brown dwarfs) is crucial to accurate determinations of the T-dwarf space density and mass function, especially since equal-magnitude binaries can introduce significant biases in photometric distance estimates. Because a recent study of slightly hotter L dwarfs indicates that 30\ equal-magnitude binaries, we believe that T dwarfs may show a similar tendency to form equal-mass pairs. Characterization of the T-dwarf multiplicity fraction is necessary if properties of the first few discoveries are to be adequately applied to larger samples uncovered later. We propose to image ten newly discovered T dwarfs using the incomparable resolution of WFPC2, where colors from the F814W and F1042M filters will provide discrimination of background sources. This imaging program will not only be able to split close binaries, but will also be capable of detecting wider companions up to four magnitudes fainter than the T dwarf primary. This will enable us to probe to temperatures around 500K, much cooler than any brown dwarf previously identified and squarely in the regime occupied by young, high-mass planets. ================================================================================ Proposal Category: GO Scientific Category: GAL ID: 8564 Title: Measuring the Evolution of the UV Upturn PI: Thomas M. Brown PI Institution: Goddard Space Flight Center We propose far-ultraviolet observations of CL1358+62, a rich, well-studied cluster of galaxies at z =0.33. These observations will provide the first completely unambiguous measurement of far-UV emission in quiescent ellipticals at moderate redshift. Theoretically, the strength of far-UV emission (relative to flux at longer wavelengths) is the most rapidly evolving feature in elliptical galaxies. Models suggest that this ``UV upturn'' can change by a factor of 25 over a few Gyr, and it is expected to fade rapidly with increasing redshift. Surprisingly, the Faint Object Camera (FOC) found strong far-UV emission in four elliptical galaxies at z=0.375, suggesting no evolution in this diagnostic between our own epoch and one 4 Gyr earlier. However, the FOC measurement was particularly susceptible to systematic errors, and it was limited to a small number of galaxies in just one cluster. In contrast to the FOC results, recent Space Telescope Imaging Spectrograph (STIS) observations at z=0.55 obtained very weak detections of ellipticals at higher redshift, as expected for ellipticals much younger than those in our own epoch. Observations with the STIS far-UV camera are not subject to the uncertainties of the FOC measurements, because the STIS camera is blind to flux at longer wavelengths. Our observations of CL1358+62 will unambiguously test the apparent lack of evolution in the UV upturn over the past 4 Gyr. ================================================================================ Proposal Category: GO Scientific Category: GAL ID: 8565 Title: Where Does Lyman Alpha Escape from Galaxy Disks? PI: William Keel PI Institution: University of Alabama The frequent detection of Lyman Alpha emission at high redshifts underscores the need to understand how it arises in nearby galaxies. Despite the obstacles posed by radiative transfer, we find empirically that significant Lyman Alpha emerges from some nearby galaxies. Data on M33, in particular, suggest that much of this escape could be from the diffuse ISM rather than from H II regions specifically, an idea with some theoretical attraction as well. This proposal examines the structure of known Lyman Alpha emission from the starburst disk of PG 0119+229, to separate the contributions of discrete and diffuse sources of this line. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8566 Title: High Resolution UV/X-ray Spectroscopy of SMC X-1 PI: Saeqa Vrtilek PI Institution: Smithsonian Astrophysical Observatory We propose simultaneous observations of the X-ray pulsar SMC X-1 and its B0 companion SK160 with HST/STIS, Chandra, and ground-based optical telescopes. We will search for correlation between orbital phase and ``bleaching'' of important P Cygni lines by X-ray photoionization (Hatchett-McCray effect). We will model the simultaneous X-ray, ultraviolet, and optical continuum emission at different phases of the superorbital period to measure changes in mass accretion rate, disk structure, and disk size. Using the Time-Tag mode, we will search in the ultraviolet for aperiodic variability near 0.1-0.2 Hz throughout the lines and continuum and for the 0.7 second X-ray pulsar period. Using the Chandra ACIS-S in CC mode we will conduct pulse-phased spectroscopy of the X-ray emission. Our multiwavelength observations will enable us to analyze the density structure and composition of the wind; set limits on the size, shape, rotation, and precession of the disk; and determine the effects of X-ray illumination on the disk, the star, and the stellar wind. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8567 Title: Confirming the parallax of the neutron star RX J185635- 3754 PI: Frederick Walter PI Institution: State University of New York Cycle 6 and 7 observations of the isolated neutron star RX J185635-3754 have revealed a motion of 0.8 arcsec in 2.5 years. This is a combination of the annual parallax and the proper motion. A third observation, planned for this fall, will formally yield sufficient information to solve for the parallax and proper motion independently. This first ever measurement of the distance of an isolated neutron star has important ramifications for astrophysics and for nuclear physics. The magnitude of the expected parallactic shift is less than one PC pixel, and must be measured against a far larger shift due to the proper motion. While this parallactic shift is in principle measurable for distance up to about 100 pc, these real data are subject to subtle instrumental effects which may skew the results. Given the scientific importance of obtaining an accurate distance, we request a fourth epoch observation to confirm the parallax. ================================================================================ Proposal Category: GO Scientific Category: ISM ID: 8568 Title: A Seminal Spectroscopic and Imagery Investigation of the Brightest Wolf-Rayet Shell Nebula: NGC 6888 PI: Reginald Dufour PI Institution: Rice University We propose to obtain HST WFPC2 imagery and STIS UV-optical-NIR spectroscopy of several regions in the brightest Wolf-Rayet Shell Nebula (WRSN), NGC 6888. The physical conditions in the wind-driven and/or stellar ejected plasma (temperature, density, ionization, and composition) of WRSN, which are dominated by strong stellar winds from hot massive stars in an advanced state of evolution, often involve emission from both shock-ionized and photoionized gas in close proximity. These new observations will comprise the first combined spectroscopy and imagery of a WRSN at a resolution sufficient (i.e., ~ 10^15 cm) to separate and individually analyze these two emission regions. We also expect to obtain the first determination of the abundance of carbon - a key element in the He-C-N nucleosynthesis chain - in WRSN, of which several are known to be nitrogen- and helium-enriched by mass loss during its previous red supergiant phase. These observations will also be used to evaluate the contribution of stellar wind-driven shock emission as a source of temperature fluctuations, important for accurate abundance determinations within this and other types of nebulae, such as planetary nebulae and H ii regions. ================================================================================ Proposal Category: GO Scientific Category: QAL ID: 8569 Title: A New Survey for Low-Redshift Damped Lyman-Alpha Lines in QSO MgII Systems PI: Sandhya Rao PI Institution: University of Pittsburgh -0.15 truein Studies have shown that most of the observable neutral gas mass in the Universe resides in QSO damped LyAlpha (DLA) systems. However, at low redshift (z<1.65), DLA can only be found by searching in the UV with HST. Such searches are crucial since z<1.65 corresponds to ~ 3/4 of the age of the Universe. The identification of significant numbers of low-redshift DLA systems is imperative if we ever hope to effectively study this cosmologically massive component of neutral gas. To this end, we recently reported on the results of our initial HST survey to study low-redshift DLA absorbers in QSO MgII systems. We discovered 14 DLA systems and had a success rate of ~14\ these results and our improved understanding of the selection criteria for successful DLA searches, we propose a new survey for low-redshift DLA lines in QSO MgII systems. With our new revised selection criteria, we can empirically show that our success rate would be ~35\ Specifically, we propose to observe the LyAlpha line of 71 MgII systems. We estimate that we will discover ~25 new DLA systems with redshift z<1.65. Finding these systems will facilitate the type of research that can be done with DLA systems. By boot-strapping from the MgII statistics, we will be able to further improve the determination of the low-redshift statistical properties of DLA (their incidence and cosmological mass density) and open up new opportunities for studies at low redshift. ================================================================================ Proposal Category: GO Scientific Category: QAL ID: 8570 Title: HS 1543+5921: A bright quasar seen through a nearby star- forming dwarf galaxy PI: Regina Schulte-Ladbeck PI Institution: University of Pittsburgh -0.15truein Recently, the nearby star-forming dwarf galaxy SBS 1543+593 (z=0.009) was discovered to be superimposed upon the bright quasar HS 1543+5921 (z~0.8, m_B=16.8). Very few such alignments are known, making HS 1543+5921/SBS 1543+593 a unique system for absorption-line studies with HST. In order to investigate the properties of SBS 1543+593 and determine the utility of future work, we request 2 orbits for a small pilot project. First, we propose to obtain a STIS spectrum which will allow us to determine the HI column density in the sight-line through the dwarf. Second, we propose to obtain a near-UV image of SBS 1543+593 with WFPC2 (to be used with ground- based images). The image will allow us to ascertain the dwarf galaxy's morphological type (spiral or irregular), details of its star formation, and investigate whether amplification bias due to the gravitational lens effect plays a role in the appearance of this improbable alignment. An exciting discovery which might result from this study is that SBS 1543+593 gives rise to a damped LyAlpha (DLA) absorption line in the spectrum of the background quasar. DLA absorbers are the reservoirs of most of the observable neutral gas mass in the Universe at higher redshifts, yet few have been directly matched with galaxies so far. There is a clear need to seize the opportunity presented by HS 1543+5921/SBS 1543+593, since a positive outcome would increase the sample of well-resolved nearby DLA galaxies. ================================================================================ Proposal Category: GO Scientific Category: QAL ID: 8571 Title: Metallicity and D/H abundance in Low-z LyAlpha Absorbers towards PG 1211+143 PI: J. Michael Shull PI Institution: University of Colorado, Boulder Our Cycle 7 STIS/G140M observations along the sightline toward PG 1211+143 reveal numerous LyAlpha absorption lines including 2 very strong LyAlpha absorbers (cz = 15,300 and 19,550 km s^-1) with associated Si III absorption. These are the first definite detections of metals in a low-z LyAlpha forest cloud; simple photoionization models suggest metallicities in the range 1--10\ sim10^17 cm^-2 in each system, we should be able to detect deuterium LyAlpha at 10--20 mAngstrom\ equivalent width, thereby testing models of D/H astration as a function of IGM metallicity, an issue of cosmological significance. We propose to obtain a 25-orbit (S/N ~ 25) STIS/E140M spectrum (1150-1740 Angstrom) at 10 km s^-1 resolution to detect or limit D I (LyAlpha) and to measure metal absorption lines (C IV, Si IV, N V, C II, Si II) observable down to below 10^-2 solar abundance (4 mAngstrom\ EW limit). This sightline is one of two prime FUSE targets for long-duration exposures in the extragalactic D/H program. FUSE will detect higher Ly-series lines and the Lyman break (accurate H I column density) and measure key metal lines (C III Lambda977, O VI Lambda1032,1038). Thus, the FUSE and STIS programs are highly interdependent. ================================================================================ Proposal Category: GO Scientific Category: QAL ID: 8572 Title: Identifying Normal Galaxies at 1.3 < z < 2.5 PI: Lisa Storrie-Lombardi PI Institution: California Institute of Technology Studies of faint, distant galaxies have greatly advanced in recent years. It is now possible to observe hundreds of galaxies out to z=1 and in the range 3 < z < 4.5, yet the redshift range 1 < z <3 remains largely unexplored. Galaxies selected by MgII absorption lines detected in quasar spectra are associated with normal galaxies up to redshifts z=1.2. We are extending this work to z = 2.5. We are already obtaining deep ground-based optical and near- infrared (VRIJK') images of fields around quasars with MgII absorbers. We propose obtaining far-UV and CCD images of our QSO fields with STIS. The aims of the observing program are: (1) Identify galaxies which produce MgII absorption using the Lyman drop-out technique. The 912Angstrom\ Lyman break is observed at 2100Angstrom\ -- 3200Angstrom\ for 1.3 < z < 2.5 so these galaxies will be absent from far-UV images below 2000Angstrom. (2) Obtain high resolution images to study MgII galaxy morphology. This can be accomplished extremely efficiently with STIS 50CCD imaging. Our main scientific goals are: (1) Find garden variety L^* galaxies at z ~ 2 when the Universe is 20-25\ as were found in the Steidel & Dickinson (1995) sample of MgII absorbers at z < 1.2. (2) Study the evolutionary history of MgII selected galaxies. If they are not typical L^* galaxies at z ~ 2 as they are at lower redshifts, we will determine the redshift at which this change occurs. ================================================================================ Proposal Category: GO Scientific Category: SF ID: 8573 Title: Newborn Planets and Brown Dwarf Companions in IC 348 PI: Kevin Luhman PI Institution: Harvard-Smithsonian Center for Astrophysics We propose to use deep WFPC2 images to search for young giant planets and brown dwarfs around ~100 low-mass stars and brown dwarfs in the nearby cluster IC 348. This cluster's age, 1-10 Myr, makes it perfectly suited for detecting such companions. While stars in star-forming regions such as Orion and Taurus are still surrounded by thick proto-planetary disks, the stars in IC 348 are old enough for most of the disks to have dissipated, yet young enough so that the newly-formed brown dwarfs and giant planets are still very luminous. By observing intrinsically faint, low-mass primaries, we should detect companions down to 3 and 7 M_ Jup at separations of 90 and 30 AU. When the results of this program are combined with other studies of planets at smaller separations around older, more massive primaries, we will better understand the properties of planetary systems as a function of primary mass and how they evolve from birth to the age of the solar system. Furthermore, because low-mass stars and brown dwarfs exist in such large numbers, this program is important in determining the frequency of planetary systems in the universe. ================================================================================ Proposal Category: GO Scientific Category: SP ID: 8574 Title: Proper Motions in Baade's Window PI: Carl Grillmair PI Institution: SIRTF Science Center/California Institute of Technology We propose to obtain third epoch WFPC2 observations of a rich field in Baade's Window. In just three orbits, we will be able to measure very accurate proper motions for ~ 13,000 Galactic bulge stars down to V = 23. Such a large number of stars, combined with color information, a relatively long baseline, and the high spatial resolution of HST, will enable an unprecedented opportunity to model the structure and dynamics of the Galactic bulge and bar populations. In addition, by selecting stars on the basis of their proper motions, we will be able to refine the color-magnitude distributions of stars in the bulge and the bar, and thus the corresponding initial mass functions and chemical enrichment histories. ================================================================================ Proposal Category: GO Scientific Category: SP ID: 8575 Title: Leo A --- Evidence for the ``Delayed Formation of Dwarfs" Scenario? PI: Regina Schulte-Ladbeck PI Institution: University of Pittsburgh Did all galaxies form at high redshift, or was the formation of certain galaxies delayed until recent (z<1) cosmological epochs? The delayed-formation -of-dwarfs hypothesis discusses how the faint blue galaxies came to be and where they are now: they represent copious dwarf galaxies that burst into stars at 0.5 0arcs3, these observations are capable of detecting companions with mass ratios M_Sec / M_Pri > 0.4. Most of our targets are at distances between ~10 and 40 parsecs. Given a binary fraction and semi-major axis distribution similar to M dwarfs, approximately 20\ are expected to be resolved. With detection limits extending well below the hydrogen-burning limit to Gl229B-like temperature, these observations, supplemented by ground-based imaging and spectroscopy, will provide a definitive measurement of the binary fraction and mass-ratio distribution in VLM dwarfs. ================================================================================ Proposal Category: SNAP Scientific Category: QAL ID: 8582 Title: UV Detectability of Bright Quasars in the Sloan Fields PI: Wei Zheng PI Institution: The Johns Hopkins University He II Ly alpha absorption at 304(1+z) Angstrom\ is a far more sensitive tracer of the intergalactic medium (IGM) than its H I counterpart. The recent detections of such absorption in four quasars, albeit with limited data quality and a small sample size, demonstrate the great potential of such a probe. The lines of sight toward the majority of z~ 3 quasars are intercepted by Lyman-limit systems, and these quasars' UV flux is cut off before reaching the He II Ly alpha feature. As a result of the SDSS, a number of bright (V<18), z>2.5 quasars are being identified. We propose a STIS snapshot survey to confirm the UV detectability of about 50 such quasars, in order to select the candidates for follow-up spectroscopic observations with STIS, COS, or FUSE. Future high-quality HST spectra of these new quasars will enable us to map the 70\ strict constraints on cold-dark-matter models of structure formation in the universe and reveal the evolution of the IGM from the epoch when the first generation of galaxies were formed down to z ~ 3. ================================================================================ Proposal Category: SNAP Scientific Category: SS ID: 8583 Title: Imaging Snapshots of Asteroids PI: Alex Storrs PI Institution: Space Telescope Science Institute We propose to obtain WFPC2 images of the fifty largest main belt asteroids that have favorable apparitions during cycle 9. The images will be searched for companion bodies, as well as mineralogical variegation on the resolved main bodies. Images in the F439W, F673N, F791W, F953N, and F1042M filters will define the 1 micron Fe^2+ feature and the possible 0.7 micron hydration feature. This will allow interpretation of compositional differences between the primary and secondary bodies, as well as any brightness variations across the disk(s) as being due solely to albedo. Because of the restriction that moving target snapshots be done under gyro control, we expect to miss 1/3 of the targets. We therefore request that each candidate be put in the snapshot pool twice, and so request 100 ``targets'' for these fifty asteroids. ================================================================================ Proposal Category: GO Scientific Category: COS ID: 8584 Title: Calibrating the Metallicity Dependence of the Cepheid PL Relation PI: Robert Kennicutt PI Institution: Steward Observatory Uncertainty in the metal abundance dependence of the Cepheid PL relation remains as one of the largest sources of systematic error in the Cepheid distance scale and in the extragalactic distance scale as a whole. We propose to directly test and calibrate the metallicity dependence of the PL relation, by obtaining independent Pop II based distances to a sample of 6 Cepheid host galaxies with (Cepheid) metal abundances (0.2--2 Z_\odot), using the tip of the red giant branch (TRGB) method. The TRGB method offers the optimal combination of precision and metallicity insensitivity for this test. When combined with currently available Cepheid and TRGB distances, these data will provide: (1) A robust empirical calibration of the Cepheid metallicity dependence; (2) Hard limits on the systematic error in H_0 from metallicity effects; (3) Empirical constraints on theoretical models of Cepheids; (4) Tight limits on other systematic errors in Cepheid distances as functions of distance, stellar crowding, and extinction; (5) A valuable Pop II based cross- check on the zeropoint of the Pop I distance ladder. ================================================================================ Proposal Category: GO Scientific Category: COS ID: 8585 Title: Cosmological Parameters from Type Ia Supernovae at High Redshift PI: Saul Perlmutter PI Institution: Lawrence Berkeley Laboratory HST can directly measure the cosmological parameters, Omega, Lambda, and thus the curvature, Omega_k, using Type Ia supernovae (SNe Ia) as calibrated standard candles. Observations of SNe Ia spanning a large redshift range are key to decoupling Omega and Lambda. In Cycle 7 (and 7-NICMOS) we studied 12 SNe in the redshift range z~ 0.35--0.85; the forthcoming measurement of Omega and Lambda is expected to have uncertainty ~11\ embarked on a program to extend the redshifts to z~1.2, starting with 2 SNe. We here propose to continue the painstaking work of obtaining a statistically significant sample across this redshift range, by studying 2 more SNe at z~ 1.2, and filling in the redshift gap with 3 SNe between z~ 0.85--1.0. Measurement of these additional high redshift SNe will dramatically shrink the major-axis of the error ellipse in the Omega_M---Lambda plane, and unambiguously determine whether the universe contains a significant vacuum energy density. These data will provide powerful constraints on SN Ia evolution and on absorption by intergalactic ``gray'' dust; it would be very difficult for either evolution or dust to alter corrected peak magnitudes in the same way as cosmology predicts over the redshift range 0= 10. The key factor that makes this project possible with the HST is the small pixel scale of the WFPC2, coupled with the small, stable PSF and superior photometric capabilities. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8593 Title: Sakurai's Novalike Object: Real-Time Monitoring of a Stellar Thermal Pulse PI: Howard E. Bond PI Institution: Space Telescope Science Institute This is a continuation of a Cycle 7-8 Long-Term program. Sakurai's novalike variable (V4334 Sgr) presents a ``once-in-a-lifetime'' opportunity for real- time observations of a star undergoing a final helium thermal pulse. The star rose from obscurity to become an 11th-magnitude, hydrogen-deficient red giant in 1995-96, and currently it is undergoing episodes of atmospheric dust formation which make it drop to quite faint magnitudes at random intervals. If it follows the pattern of the similar object V605 Aql, it will soon begin evolving back to high temperature. During the subsequent few years, it would then begin to (re)-ionize its large, faint planetary nebula, and we should be able to witness the re-establishment of a fast stellar wind as the effective temperature increases. This is a Target-of-Oppurtunity proposal. When the star does start to become hot again, we will start using STIS to monitor the spectroscopic development of the star in the UV at regular intervals, continuing over the next 3 Cycles. We will also use WFPC2 once a year to monitor expansion of the ejecta. In combination with ground-based monitoring (optical, IR, and mm), we will thus produce the first detailed case study of a thermal pulse, as the star re-traces its evolution across the HR diagram from the AGB to the planetary-nebula phase. ================================================================================ Proposal Category: GO Scientific Category: ISM ID: 8594 Title: H-deficient condensations in PNe -- a key to discrepancies in abundance determinations PI: Xiao-wei Liu PI Institution: University College London own and other galaxies rests on emission line nebulae. Our recent CNO abundance determinations for PNe using optical recombination lines (ORLs) have yielded abundances systematically higher than the `standard' values deduced from UV/optical collisionally excited lines (CELs), with discrepancies covering a wide range from 1--20. In the extreme case of NGC 6153, multi- waveband analysis has yielded CNO and Ne abundances from ORLs which are all about a factor of ten higher than the CEL values. Temperature fluctuations and density inhomogeneities fail to explain all the available data. Instead our analysis indicates that NGC 6153 may have experienced a recent ejection of H-deficient knots, similar to those observed in the `born-again' PN A 30. We propose to obtain deep STIS long-slit spectra for the well-resolved H- deficient knots of A 30 and to search for such knots in NGC 6153. The data will yield the spatially resolved temperature, density and ionization structure of the knots in A 30, and, for the first time, accurate ORL C and O abundances for them. The results will lead to a much better understanding of the physics of such knots and their effects on abundance determinations. The observations of NGC 6153 will allow us to test if the observed central peaking of its ORL C and O abundances is a consequence of a central concentration of similar ================================================================================ Proposal Category: GO Scientific Category: ISM ID: 8595 Title: Does the D/H Ratio Vary in Local Interstellar Gas? PI: Meena Sahu PI Institution: NASA/Goddard Space Flight Center Measurements of the D/H ratio in the Local Interstellar Cloud (LIC) are consistent with 1.5 +/- 0.1* 10^-5, while for other clouds within ~ 100 pc, the measurement uncertainties are larger. Current data provide limited information on whether the D/H ratio varies between the LIC and the other clouds. We propose to determine if the D/H ratio varies, by high-precision D/H measurements and by devising strategies to reduce both random and systematic errors. STIS E140H & E230H mode (R~ 150,000) data will resolve the velocity components and allow reliable determinations of component-to- component variations. Two target white dwarfs (WDs) HZ 43 and GD 153 are chosen because EUVE data show low H i column densities, thereby reducing the probabilities of multiple velocity components and saturation of the D i line. The WDs have pure-H atmospheres, so contamination of the interstellar lines by photospheric metal lines is not an issue. Physically realistic NLTE models will be used to accurately predict the WD Lyman-Alpha contributions. HST-STIS, with its higher velocity resolution (compared to GHRS & FUSE), wider wavelength coverage, and better scattered light corrections (compared to GHRS) is the facility best suited for this project. We have demonstrated the capabilities of STIS in our study of the G191-B2B sightline, which is the only published STIS measurement of the D/H ratio to date. ================================================================================ Proposal Category: GO Scientific Category: QAL ID: 8596 Title: Environmental Pollution: The Outflow in the Archetypal Galaxy-Quasar Pair NGC3067/3C232 PI: Max Pettini PI Institution: Institute of Astronomy Galactic-scale outflows are now known to be a common occurrence in star- forming galaxies, in the nearby universe and at high redshift. These superwinds have fundamental astrophysical implications for regulating star formation, determining the evolution of the host galaxies, disseminating the products of stellar nucleosynthesis over large volumes, and are probably responsible for many of the metal absorption lines seen in QSO spectra. In order to understand the physical process involved, we have been developing detailed chemo-spectro-dynamical models which, however, suffer from a lack of direct observational constraints. We propose to remedy this situation by detecting the hot gas from NGC3067, a galaxy with concentrated nuclear star formation giving rise to an outflow seen in X-rays, in STIS G140M spectra of the background QSO 3C232. Although this is one of the best studied QSO-galaxy pairs, there have been no high-resolution observations yet targeted at absorption lines of highly ionized species, as requested here. In addition, STIS spectroscopy of the nuclear regions of the galaxy will establish the age and properties of the stellar population, so far only known from imaging data. By bringing together X-ray, UV and optical data we will obtain the first quantitative description of a galactic outflow, its relation to the star- formation activity in the galaxy, and its effects on the interstellar and intergalactic medium. ================================================================================ Proposal Category: SNAP Scientific Category: AGN ID: 8597 Title: The Fueling of Active Nuclei:, Why are Active Galaxies Active? PI: Michael Regan PI Institution: Carnegie Institution of Washington Accretion onto massive black holes is believed to be the energy source for AGN. However, evidence for black holes in quiescent galaxies has also been reported; why are these galaxies inactive? One possibility is that active galaxies are better at providing fuel to the nuclear region than quiescent galaxies. For the ISM to fuel a massive black hole it must lose significant amounts of angular momentum. Although angular momentum can easily be removed by stellar bars, recent ground-based studies of Seyferts show that the fraction of bars in active galaxies is no higher than in normal galaxies. Other possible fueling mechanisms such as ``bars-within-bars'' or nuclear spirals cannot be investigated from the ground because they are relatively small features in the ISM. Recent HST observations using optical - near- infrared color maps to probe the morphology of the ISM at high resolution have shown that the majority of Seyfert galaxies have nuclear dust spirals. We propose to obtain WFPC2 snapshots of a sample of primarily quiescent galaxies which we will combine with existing NICMOS images to form color maps to determine if quiescent galaxies also have a large fraction of nuclear dust spirals. This will allow us to determine if nuclear spiral arms are the distinguishing feature that makes active galaxies active. Since the database created will be invaluable for other studies of spiral galaxies, we are waiving our proprietary period. ================================================================================ Proposal Category: SNAP Scientific Category: AGN ID: 8598 Title: Snapshot Survey of Extended OIIILambda5007Angstrom\ Emission in Seyfert Galaxies PI: Henrique Schmitt PI Institution: Space Telescope Science Institute We propose a snapshot survey of narrow band OIIILambda5007Angstrom\ images for a well defined sample of 88 Seyfert galaxies (29 Seyfert 1s and 59 Seyfert 2s), 18 of which already have data in the archive, selected from a mostly isotropic property, the 60Mum flux. These data will be used: 1) to determine the origin of the misalignment between the accretion disk axis and the host galaxy plane axis, which can be due to mergers with other galaxies, or by the self induced radiation warping; 2) to compare the size and shape of the NLR of Seyfert 1s and Seyfert 2s, and to study the frequency of conically shaped Narrow Line Regions (NLR) in Seyfert galaxies, which are usually unresolved from ground-based observations; 3) estimate the importance of shocks to the ionization of the NLR. We aim to provide a critical test of the applicability and limitations of the Unified Schemes that currently are the framework for understanding Seyfert galaxies and their luminous counterparts. ================================================================================ Proposal Category: SNAP Scientific Category: GAL ID: 8599 Title: A Census of Nuclear Star Clusters in Late-Type Spiral Galaxies PI: Torsten Boeker PI Institution: Space Telescope Science Institute Recent HST observations have revealed that many spiral galaxies have a prominent star cluster in their dynamical center. Such a cluster can plausibly have significant influence on the formation and/or evolution of the galaxy bulge, which is an important new aspect in the ongoing discussion about the origin of the Hubble sequence. While existing HST data indicate that nuclear clusters can occur in spirals of all types, statistics for cluster frequency, size, and luminosity as a function of Hubble type are incomplete. There is a particular lack of data for late type spirals, because most HST studies were biased towards earlier Hubble types. To fill this gap, we propose a WFPC2 I- band snapshot survey of a well-defined sample of nearby, face-on spiral galaxies of type Scd or later. Given the sizes of known nuclear clusters (R_eff~ 0.2^ ), HST provides an order of magnitude contrast improvement over ground-based imaging, crucial for an unambiguous identification of the cluster. The data will also yield cluster sizes and unblended luminosities, which are impossible to obtain from the ground. This program will be the first systematic census of nuclear star clusters in late-type spirals. As such, it will provide a valuable catalog for follow-up spectroscopy to study the stellar populations, masses, and ages of these clusters, all of which are important diagnostics for understanding their formation mechanism and possible influence on the surrounding bulge. ================================================================================ Proposal Category: SNAP Scientific Category: GAL ID: 8600 Title: Dwarf Elliptical Galaxy Snapshot Survey III PI: Henry C. Ferguson PI Institution: Space Telescope Science Institute We propose to extend our V and I snapshot survey of nearby dwarf elliptical (dE) galaxies to include a sample of 30 bright dE (M_V < - 15.7) with significant globular cluster (GC) populations. This survey will provide important information on the globular cluster systems of such galaxies and the properties of their cores and nuclei. The high resolution of HST allows us to identify globular cluster candidates and classify more accurately a galaxy as nucleated or non-nucleated. Our results from the Cycle 6 survey show that dE have globular cluster specific frequencies (S_N) similar to those of giant ellipticals. Nucleated dE have higher S_N than non-nucleated dE, and show a trend of increasing S_N with fainter luminosities. We have also studied the spatial distribution of the globular clusters and an interesting (lack of a) trend is emerging. The globular cluster surface densities follow the luminosity profiles of the underlying galaxies, on average, and there is no segregation by luminosity. This is an interesting result, if confirmed, because the dynamical friction timescales for dE galaxies are significantly shorter than a Hubble time. With better statistics, analysis of the cluster spatial distribution can place constraints on the ages of the clusters and the dark matter, and offer tests of the universality and evolution of the globular cluster luminosity function. ================================================================================ Proposal Category: SNAP Scientific Category: GAL ID: 8601 Title: A Snapshot Survey of Probable Nearby Galaxies PI: Patrick Seitzer PI Institution: University of Michigan The census of galaxies in the Local Volume of space is very incomplete, particularly at the faint end. We propose to continue our very successful snapshot survey to use the high spatial resolution of HST to determine whether selected galaxies are nearby on the basis of resolution into stars, and the magnitudes and colors of the brightest stars. In the first 2 months of the cycle 8 proposal, data was obtained on 18 candidates, and 15 (83 \ on the magnitudes of the brightest stars. We are rapidly increasing the number of confirmed galaxies within 4 Mpc. Our sample is chosen from the survey by team members Karachentsev & Karachentseva (KK98) of some 260 nearby dwarf galaxy candidates. Our F606W & F814W snapshot survey will concentrate on 125 unobserved candidates. One HST orbit per galaxy results in a distance from the magnitude of the tip of the red giant branch (TRGB) and is sufficiently deep to identify the brightest stellar population if the galaxy is within 4 Mpc. Keck, VLT, and other large telescopes will be used for spectroscopic follow-up for abundances and kinematics. The survey has already discovered two possibly isolated dwarf galaxies not associated with any galaxy or group. Since the sample to be observed is chosen from an all sky sample, we will be able to determine if there is a significant number of such isolated dwarf galaxies. ================================================================================ Proposal Category: SNAP Scientific Category: HS ID: 8602 Title: A Snapshot Survey of the Sites of Recent, Nearby Supernovae PI: Alex Filippenko PI Institution: University of California at Berkeley During the past few years, the Lick Observatory Supernova Search (LOSS) and the Beijing Astronomical Observatory Supernova Search (BAOSS) have found a total of 76 supernovae (SNe), 62 of them in relatively nearby galaxies (cz <= 6000 km s^-1). Most of the nearby objects were discovered before maximum brightness. All have follow-up photometry and spectroscopy; they include some of the best-studied SNe to date. We propose to conduct a WFPC2 snapshot survey in V and I of the sites of the nearby SNe, which have precisely known positions, to obtain high-resolution information on their local environment. For example, we will see whether SNe of a given kind tend to occur close to star clusters, or in dusty regions, or in old (red) stellar populations. This will give important clues to the nature of their progenitor stars, with ramifications for many areas of astronomy (e.g., stellar evolution, nucleosynthesis, cosmology). For some of the most recent or unusually long- lived SNe, the new HST data will provide late-time photometry that is superior to what we can obtain from the ground. This proposal is similar, but complementary to, our archival proposal in which existing HST images from other programs are used to glean information about the environments of SNe. To make the data readily available to other researchers studying these SNe, we waive the entire proprietary period. ================================================================================ Proposal Category: SNAP Scientific Category: HS ID: 8603 Title: Secular changes in the temperatures and radii of extreme helium stars PI: Simon JEFFERY PI Institution: Armagh Observatory Extreme helium stars (EHEs) are luminous stellar remnants evolving rapidly to become white dwarfs. They represent an important stage in the evolution of at least some low-mass stars, and are closely related to the R Coronae Borealis variables. Models do not agree about their origin, nor about what fraction of normal stars pass through this phase, in which the stars have been completely stripped of their outer layers. The models do predict that EHEs are contracting and provide rate predictions and evolutionary lifetimes. First and second epoch IUE observations have shown that these contraction rates can be measured. We propose HST/STIS observations of 15 EHEs which, together with IUE data, will give a 20-year baseline of ultraviolet spectrophotometry. These observations will provide effective temperatures and angular radii with an internal accuracy for individual stars of $~1\ precision which cannot be achieved from optical or other diagnostics. From these measurements we will measure precise contraction rates for a larger sample of targets and obtain direct tests of the evolution models. Building on the IUE archive, the higher quality of HST data will provide a foundation dataset for establishing fundamental quantities (e.g. extinction) and for studying evolutionary changes in EHEs into the next century and beyond. ================================================================================ Proposal Category: SNAP Scientific Category: SP ID: 8604 Title: Stellar Populations Across the Small Magellanic Cloud: History and Structure PI: Eline Tolstoy PI Institution: European Southern Observatory The Small Magellanic Cloud (SMC) is an extraordinary galaxy. It is the nearest example of a low metallicity, star-forming dwarf irregular, contains a wide range of stellar ages, and is distorted by interactions with the Milky Way and its close companion, the Large Magellanic Cloud. We propose to investigate the structure and evolutionary history of the SMC by obtaining a series of 50 three-color SNAPshots with WFPC2 of selected SMC regions. With this polling of SMC field star properties, we will produce color-magnitude diagrams (CMDs) in the U, V and I bands which will reach V~23.5 in regions too crowded to be observed accurately from the ground. We will use these data for investigations of two major topics: (1) the star formation history of the SMC, by quantitative matching between models and data using a sophisticated numerical approach which properly accounts for errors and other uncertainties. (2) the structure of the SMC along our line of sight. The galaxy is thought to be considerably distended in this direction and we will put constraints on this from the width of the observed lower main sequence. In addition, by obtaining accurate photometry for about 100,000 stars in each region, our CMDs will provide an excellent basis for comparisons with evolutionary tracks of low metal stars in the few solar masses range. ================================================================================ Proposal Category: GO Scientific Category: AGN ID: 8605 Title: Stellar-Dynamical Measurements of the Black Hole Masses of Reverberation-Mapped AGN PI: Gary Bower PI Institution: National Optical Astronomy Observatories The broad emission line regions of 20 AGN have been successfully reverberation mapped in intensive international monitoring campaigns, allowing model dependent determinations of the central mass. This determination depends on the hypothesis that the dynamics in this gas are dominated by gravity, consistent with the detection of the expected Keplerian decline in velocity with radius in the best studied case (NGC5548). However, when normalized by the bulge mass of the host galaxy, the central masses in these 20 AGN are over an order of magnitude less massive than the compact dark masses found in normal galaxies. If the masses determined by reverberation mapping can be independently verified, this technique could potentially be used to measure the evolution in the masses of the population of supermassive black holes over cosmic time and determine these masses in radio-quiet and radio-loud AGN spanning a huge range in luminosity. We therefore propose to use STIS to measure the stellar dynamics in the type 1 Seyfert nucleus in NGC3227, in which the measurements will be the most straightforward by far. If the reverberation mapped mass is correct, we will see its dynamical signature in these new data. ================================================================================ Proposal Category: GO Scientific Category: AGN ID: 8606 Title: Determining the Nature of the Variable Absorption in AGN: Monitoring NGC 3783 with HST and Chandra PI: D. Michael Crenshaw PI Institution: Catholic University of America, STIS Science Team About 60\ characterized by high ionization (C IV, N V), moderate widths (30 -- 300 km s^-1), significant outflow velocities (up to 2500 km s^-1), and variability on time scales as small as days. Seyferts with UV absorption also show variable X-ray ``warm absorbers'', characterized by O VII and O VIII absorption edges, which suggests a common origin. The frequent occurrence of intrinsic absorption indicates that an important component has been missing from our overall picture of active galaxies. To understand the nature and origin of this component, and thereby use it as a probe of the active nucleus, we must know its location, physical conditions, and kinematics. Variability monitoring is the key to understanding the absorbers, by providing their radial locations, densities, and evolution in ionization, column density, velocity, and coverage of the inner active nucleus. However, our search for the nature of the absorption has been hampered by the lack of an intensive UV and X-ray monitoring campaign at high spectral and temporal resolutions. HST/STIS and Chandra are ideal instruments for this pursuit, and NGC 3783 is an ideal target, because it shows extremely variable absorption and rapid continuum variability in both the UV and X-rays. ================================================================================ Proposal Category: GO Scientific Category: AGN ID: 8607 Title: Completing the Local AGN Inventory: The AGN Content of Composite Nuclei PI: Luis Ho PI Institution: Observatories of the Carnegie Institution of Washington Knowledge of the local space density of AGNs is of fundamental importance to a number of astrophysical problems. A significant fraction of nearby galaxies have nuclei whose spectra are intermediate between those of LINERs and nuclear starbursts. These ``transition objects'' may be composite systems that contain both a central AGN and circumnuclear star formation. We will test this hypothesis by using STIS to obtain spatially-resolved optical spectra of a well-defined sample of 15 nearby (<= 17 Mpc) transition nuclei selected from the extensive ground-based survey of Ho, Filippenko, and Sargent. The physical origin of these objects affects the census of AGNs in nearby galaxies, the nature of nuclear star formation, and the possible connection between starburst and AGN activity. We will use the G430L and G750M gratings to cover the most important diagnostic emission lines in order to search for line-ratio variations across the nuclear region. If the two-component model for transition nuclei is correct, we expect the spectra to change from H II\ region-like to AGN-like as the center of the galaxy is approached. We will also use the high-resolution spectra to search for weak broad H\al\ emission, the classical signature of AGN activity, at a level of sensitivity far greater than is possible from the ground. Finally, the spectra will provide a rich source of nebular diagnostics to systematically study the physical properties of nuclear H II\ regions. ================================================================================ Proposal Category: GO Scientific Category: AGN ID: 8608 Title: Simultaneous HST, Chandra, and FUSE Spectroscopy of NGC 4151 PI: Gerard Kriss PI Institution: Space Telescope Science Institute Absorption by warm, ionized gas at UV and X-ray wavelengths is proving to be a common feature in Seyfert 1 galaxies, showing its presence in well over half the galaxies observed. In some cases, like NGC 4151 and NGC 3516, the absorption is seen over a wide range of ionization states, and it is optically thick at the Lyman limit, thick enough to potentially collimate the ionizing radiation in these objects and produce ``ionization cones" visible in emission -line images. Thus understanding this warm absorbing gas and its origin may help us to understand how radiation is collimated in AGN, and it may provide additional clues to the differences and similarities between Type 1 and Type 2 AGN. The proximity and brightness of NGC 4151 make it a key object for understanding the structure of AGN. We propose to obtain simultaneous spectroscopy of the absorbing gas in NGC 4151 using the STIS echelle modes on HST, FUSE, and Chandra. These observations will allow us to determine the ionization states of each of the 8 kinematic components present in the absorbing gas in NGC 4151, and to resolve the persistent discrepancies between the gas columns inferred for the UV and X-ray absorption over the past two decades. The simultaneity will avoid any ambiguity due to the known variability in the UV and X-ray absorption. ================================================================================ Proposal Category: GO Scientific Category: AGN ID: 8609 Title: Host galaxy luminosities of the most luminous QSOs PI: Lance Miller PI Institution: Oxford University Department of Physics What are the factors that determine whether a galaxy is host to a luminous QSO? Recent evidence indicates that host galaxy spheroid mass is a key factor: we want to test the relationship between host galaxy and QSO luminosity at the highest feasible QSO luminosities by measuring the luminosities and profiles of host galaxies for QSOs with -25.8 > M_V > -27.6. Current data in this area are conflicting, and we aim to make a definitive experiment that takes careful account of problems caused by extended line or continuum emission around QSOs, relativistic beaming, gravitational lensing and galaxy interactions. ================================================================================ Proposal Category: GO Scientific Category: AGN ID: 8610 Title: A Black Hole Offset from the Host Galaxy Mass Center? PI: Carole Mundell PI Institution: University of Maryland It has been suggested that the central regions of many galaxies are unlikely to be in a static steady state, with instabilities caused by sinking satellites, the influence of a supermassive black hole or residuals of galaxy formation, resulting in the nuclear black hole orbiting the galaxy center. The observational signature of such an orbiting black hole is an offset of the active nucleus (AGN) from the kinematic center defined by the galaxy rotation curve. This orbital motion may provide fuelling of the AGN, as the hole `grazes' on the ISM, and bent radio jets, due to the motion of their source. The early type (E/SO) Seyfert galaxy, NGC2110, with its striking twin, `S'- shaped radio jets, is a unique and valuable test case for the offset-nucleus phenomenon since, despite its remarkably normal rotation curve, its kinematically-measured mass center is displaced both spatially (260 pc) and kinematically (170 km s^-1) from the active nucleus, as seen both in optical and radio studies. However, the central kinematics, where the rotation curve rises most steeply, are inaccessible with ground-based resolutions. The proposed WFPC2 imaging and long-slit STIS spectroscopy of NGC 2110 will enable determination of the structure and kinematics of gas moving in the galactic potential on subarcsecond scales and investigate the origin of the off-set nucleus. ================================================================================ Proposal Category: GO Scientific Category: COS ID: 8611 Title: UV Observations of Nearby 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 throughly 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/CCD UV spectra of five nearby (0.02 < z < 0.08) SNe Ia in the Hubble Flow. 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 the z > 0.8 SNe Ia observed by both the Supernova Cosmology Project and the High-Z Supernovae Search Team this data is crucial for proper cross-filter k-corrections and calibration of the supernova photometry. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8612 Title: Boron in the Lithium-Rich K-Giants: A Critical Test of Deep Stellar Mixing Versus Brown-Dwarf Ingestion PI: Ramiro de la Reza PI Institution: Observatorio Nacional We will observe the B I 2500Angstrom\ lines in four Li-rich K-giants using HST with STIS/G230M in order to test two different evolutionary scenarios invoked to explain the high Li abundances: the cool bottom process (CBP) versus the possible accretion of brown dwarfs/planets. This test utilizes the two following properties of boron: among the three light elements (Li, Be, and B) which are easily destroyed in stars by (p,Alpha) reactions, B is the least fragile to nuclear destruction. In addition, unlike Li which can be created under certain conditions in stellar mixing, B can only be destroyed. The hypothetical mixing mechanism, CBP, produces Li by introducing deeper mixing to hotter layers such that ^7Li is created via ^3He(alpha,Gamma)^7Be(e^-,anti- Nu)^7Li. A by-product of CBP is the total destruction of pre-existing Be and B. If B I is absent from the spectra, we will prove that deep mixing has occurred. In an accretion scenario, the increase in the Li abundance caused by the deposition of fresh material onto the red giant from a substellar mass companion will also result in an increase in the Be and B abundances. Because B is more robust to nuclear burning than Be, as well as initially being 20 times more abundant, spectroscopy of the B I lines will provide a solid and definitive test of whether the process that creates these chemically peculiar giants is a new type of internal mixing, or the ingestion of a substellar mass companion. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8613 Title: Coordinated Observations of Stellar Flares on AD Leo PI: Suzanne Hawley PI Institution: University of Washington We will obtain high resolution HST/STIS spectra of the dMe star AD Leo during periods of quiescence and during flares to study the physics of atmospheric heating in flare stars. The HST observations will form an essential part of a large, coordinated observing campaign including FUSE, EUVE, and ground-based observations (both multicolor photometry and high resolution optical spectroscopy). The STIS spectra, in combination with data from the other satellites, will allow us to determine the structure (during quiescence) and evolution (during flares) of the temperature and density in the corona, transition region, and chromosphere. These data will provide strong empirical constraints on our current generation of flare evolution models. The uniquely high spectral resolution of the STIS data will also allow us to directly observe the dynamic effects of the chromospheric shocks that are predicted by the models. In addition, we will search for significant red- shifted emission in the hydrogen Lyman-Alpha line during the flare rise phase, which is a signature of an energetic proton beam. The existence and role of proton beams in both solar and stellar flares is currently a subject of considerable debate. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8614 Title: NUV Extension of the Arcturus Project: Probing the Onset of Chromospheric Heating PI: Kenneth Hinkle PI Institution: National Optical Astronomy Observatories Two stars have multi-wavelength atlases at resolutions (R>= 100,000) high enough to resolve dynamically interesting line structure: the Sun (G2 V) and Arcturus (K2 III). These canonical atlases provide an astrophysical test bench for studying the effects of temperature, gravity, and metalicity in cool stars. We have produced high resolution spectral atlases of the Sun from 22 Mum through the visible, as well as a high resolution spectral atlas of Arcturus from 5 Mum through 0.9 Mum. These atlases are widely used for line identification, calibrating atomic data, testing model atmospheres, studying stellar granulation, etc. We are currently finishing a major new digital atlas of the Sun and Arcturus from 3600--9000 Angstrom\ at R=150,000 (to be published next year as an ASP monograph). We propose to extend the spectral coverage of these atlases down to 2124 Angstrom, using existing STIS spectra of Alpha Cen A (as a solar proxy) and new STIS observations of Arcturus. The NUV spectrum is astrophysically important because it encompasses the transition from the photosphere through the temperature minimum into the chromosphere. Modeling the spectroscopic transition from absorption to emission lines will provide important semi-empirical constraints on the poorly understood nonradiative heating processes that give rise to chromospheres in evolved stars. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8615 Title: Ultraviolet Spectroscopy of R Coronae Borealis Stars -- Broad Lines from an Accretion Disc? PI: David L. Lambert PI Institution: University of Texas at Austin STIS spectra of three R Coronae Borealis (RCB) stars will provide novel data on hot gas near these stars; such data can be obtained only from HST. RCBs are hydrogen-deficient and fade at unpredictable times as a carbon soot cloud obscures the star. Optical spectra taken when a star has faded reveal an emission line spectrum containing sharp (FWHM ~eq 15 km s^-1) and broad (FWHM ~eq 250 km s^-1) lines. The lattter are of much higher excitation than the former. For R CrB, it has been suggested that the broad lines arise from an accretion disk around a compact secondary. These optical lines are visible only during the infrequent extreme fadings of a RCB. Although IUE spectra reveal high-excitation emission lines at maximum light, the IUE spectra lack the spectral resolution to distinguish broad from sharp lines. STIS spectra will resolve the broad-line from a sharp-line component, and, in the case, of R CrB, where repeat visits are requested, be used to search for velocity variations as the companion orbits the RCB. In addition, the line intensity ratios will provide new estimates of the physical conditions of the gas emitting the broad lines. This proposal may help to answer the question -- How are RCBs formed? And this answer may show that, although RCBs are rare, many low mass stars evolve through the RCB on their path to extinction as a white dwarf. ================================================================================ Proposal Category: GO Scientific Category: CS ID: 8616 Title: Masses of Pre-Main Sequence Binaries PI: Michal Simon PI Institution: State University of New York We propose to continue to map the orbits of young star binaries in the Taurus and Ophiuchus star forming regions. Our goal is to measure their masses dynamically. This is important because there are still no low mass young stars with reliably known masses so calculations of their evolution to the main sequence are uncalibrated. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8617 Title: Ultraviolet Spectroscopy of Hot Horizontal-Branch Stars in the Globular Cluster M13 PI: Bradford Behr PI Institution: California Institute of Technology Blue horizontal-branch (BHB) stars in the metal-poor globular clusters M13 and NGC 6752 have recently been found to exhibit remarkable metallicity enhancements and helium depletion relative to the canonical cluster composition. These abundance anomalies are most likely due to diffusion processes --- radiative levitation of the metals, and gravitational settling of helium --- in the stable radiative atmospheres of these hot stars. With available ground-based facilities, we have observed stars in M13 as hot as 19000 K, but beyond this point we are constrained by low V- and B-band flux and an insufficient number of visible-wavelength spectral lines. We therefore propose HST/STIS spectroscopic observations in the wavelength range 1700--3100 Angstrom\ to extend the abundance measurements in M13 to yet hotter stars. Such measurements will provide a new and important confrontation between theory and observations of the diffusion mechanisms, and will also offer insights into poorly-understood aspects of CMD morphology, including the BHB `gaps' and overluminous BHB stars observed in many clusters. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8618 Title: FGS parallaxes of magnetic CVs PI: Klaus P. Beuermann PI Institution: Universitaets-Sternwarte Goettingen Trigonometric parallaxes of cataclysmic variable (CVs) are needed to obtain reliable information on luminosities, accretion rates, and on radii and masses of the stellar components. They are also needed to derive the space density, an important ingredient for theories of CV evolution. Photometric and spectroscopic parallaxes of CVs are notoriously uncertain because the stellar components have properties different from single field stars. Obtaining trigonometric parallaxes of CVs will allow us to understand to what extent the other methods are applicable to CVs and why they fail in certain cases. Trigonometric distances are also needed for those CVs to which the other methods can not be employed, e.g. because the secondary star, serving as a standard candle, is not detectable. In summary, trigonometric parallaxes are essential to our understanding of CVs. We propose to obtain accurate trigonometric parallaxes of three magnetic cataclysmic variables (CVs) which are among the brightest of their class, are not accessible to other methods of distance determinations, and have largely defied physical interpretation so far. We will: (1) clarify the nature of the enigmatic system EX Hya; (2) measure the radius (and thereby the mass) of the white dwarf in EF Eri, obtain tight limits on the magnitude of its (near-)degenerate secondary star, determine the mass-transfer rate supposedly driven by gravitaional radiation; and (3) decide on the nature of AH Men, one of the brightest long-period (probable) Intermediate Polars. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8619 Title: Critical spectroscopic variations in Eta Carinae PI: Kris Davidson PI Institution: University of Minnesota The very massive, unstable, persistently enigmatic star Eta Carinae has implications for several branches of astrophysics. While HST has produced a series of remarkable discoveries concerning this object, the nature of the central star remains elusive. Now, however, recent developments offer, for the first time, an approach that can settle certain long-standing questions which have been obstacles to understanding this unique object. A 5.5-year spectroscopic and X-ray cycle has been confirmed. STIS now provides the most promising and very likely the only way to test whether Eta Car is a 5.5-yr binary system. If it is, STIS will also allow us to constrain the parameters, needed to assess the companion star's possible role in past outbursts and ejecta. If the data conflict with binary models, then the 5.5-yr effect is probably a thermal cycle which will give novel information about the star's structure. In addition to the periodicity, a large, almost unprecedented brightening, first noticed in HST data, has occurred since 1997 and merits followup observations. We sense a breakthrough in the periodicity and the brightening, if Eta Car can be observed repeatedly with STIS through the current 5.5-year period, 1998.0---2003.5. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8620 Title: Taking a glance at the beating heart of 4 Draconis PI: Boris T. Gaensicke PI Institution: Universitaets-Sternwarte Goettingen 4 Dra is a unique triple system containing a magnetic cataclysmic variable (AM Her-type) and an M3 III giant. Even though the M-giant completely dominates the optical emission of the system, we can learn much from 4 Dra about the accretion physics in and the evolution of AM Her stars, because: (a) 4 Dra is the second brightest AM Her star in the ultraviolet, (b) 4 Dra is one of the very few cataclysmic variables with a good HIPPARCOS parallax (d~180 pc), and, in addition, (c) 4 Dra is so far the only bright CV for which an estimate of the age, ~10^8 yrs could be derived. We propose an in-depth HST/STIS echelle study of the AM Her star in 4 Dra. Our scientific goals are twofold. (1) We will derive the fundamental properties of the accreting magnetic white dwarf, such as its photospheric temperature, the temperature and the size (lateral extent) of the accretion-heated pole cap, and the chemical composition of the accretion-enriched atmosphere. (2) We will use the HST/STIS echelle spectra for Doppler mapping of the UV line emission. The HST maps of LineCIV1550 and LineHeII1640 emission will probe the velocity field and ionization structure in the complete accretion flow, including the irradiated face of the donor star, the ballistic gas stream from that star to the white dwarf magnetosphere, the threading region between the stream and magnetosphere, the magnetically controlled flow down to the standoff shock, and the surrounding heated regions at the white dwarf surface. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8621 Title: The Galactic Abundance Gradients of Boron and Iron PI: David L. Lambert PI Institution: Department of Astronomy, University of Texas This proposal aims to provide the first measurement of the Galactic abundance gradients for Boron and Iron. Boron abundances will be obtained for 5 B-type stars (with Galactocentric distances between 4--15 kpc) from the B iii 2066Angstrom\ line. Optical spectroscopy of these (and other B-type) stars has yielded abundance gradients of -0.07 dex kpc^-1 for N & the Alpha-elements (O,Mg,Si). Determination of Boron abundances require UV spectra and HST/STIS. It is significant that stellar nucleosynthesis which is the leading source of oxygen (via Type II SN) is unlikely to be a major contributor to B synthesis (spallation being the leading candidate). Hence, a measurement of the B abundance gradient provides novel information on the gradient of cosmic ray flux in the Galaxy. The same STIS spectra will also provide Fe iii lines that will be used to obtain the first estimate of the present abundance gradient for iron (thought to originate predominantly in Type I SN). Recent advances in modelling the chemical evolution of the Galactic disk have led to definite predictions of the spatial variation of the Alpha/Fe ratio in competing Galaxy formation scenarios, viz. the biased infall and biased outflow models. This study should yield differential Fe abundances accurate to +/-0.1 dex -- which will allow a Alpha/Fe gradient to be compared directly with theory, as a critical test of formation models. ================================================================================ Proposal Category: GO Scientific Category: ISM ID: 8622 Title: The Interstellar Isotopic Ratio of Boron toward Omicron Persei and Nearby Sight Lines PI: David L. Lambert PI Institution: University of Texas at Austin The isotopic ratio ^11B/^10B will be determined for diffuse interstellar material along lines of sight to 40 Persei, o Persei, Zeta Persei, and X Persei that pass close to the star-forming region IC 348. High-resolution spectra of the Li, i 6707Angstrom\ line toward o and Zeta Per show remarkably different isotopic ratios for lithium. Particularly striking is the ratio ^7Li/^6Li ~eq 3 for o Per while Zeta Per shows a quasi-solar (~eq 10) ratio. The significance of the very low ratio for o Per is that it is essentially the value predicted for production by relativistic cosmic rays through spallation reactions; it is the only interstellar or stellar measurement that approaches this theoretical value. This discovery provides a novel opportunity to measure the isotopic B ratio of gas with a Li concentration dominated by spallation induced by relativistic cosmic rays. Feasibility of isotopic measurements has been demonstrated by our GHRS observations of the interstellar B, ii 1362Angstrom\ resonance line that provided the first extra-solar measurement of the ratio. Comparison of the observed and predicted isotopic B (and Li) ratio will test the relative importance of B synthesis by cosmic rays and Type II supernovae, and test proposals that invoke high-fluxes of high-energy particles in star-forming regions as major players in light element synthesis. ================================================================================ Proposal Category: GO Scientific Category: ISM ID: 8623 Title: HST, Chandra, and FUSE Studies of Interstellar Material toward HD 24534 (aka X Persei) PI: Theodore P. Snow PI Institution: University of Colorado We are proposing new HST/STIS high-resolution UV spectroscopic observations of the reddened star HD 24534 (aka X Persei), in order to: (1) establish accurate gas-phase column densities for elements other than carbon and oxygen (for which high-quality data already exist), for the purpose of deriving (in conjunction with FUSE and Chandra observations) absolute depletions of several key elements; and (2) further pursue molecular abundances toward this star, to supplement HST/GHRS data obtained earlier which showed that this line of sight supports a rich chemistry. The depletion work will focus on magnesium, silicon, and iron, while the molecular observations will entail searches for vibrationally excited H_2, an important indicator of cloud physical conditions; and sulfur- bearing species (such as SO, CS, and SH), which represent an important unknown in current models of interstellar cloud chemistry. HD 24534 is the best possible target for this work, because it is the brightest star available that lies behind a translucent line of sight with high molecular abundances, and because it is also an x-ray source whose spectrum is ideally suited for the measurement (through x-ray absorption and scattering) of total (gas plus dust) abundances in the line of sight. This will be the first line of sight for which depletions have been determined independent of any assumed ``cosmic'' abundance standard such as the sun or other stars. ================================================================================ Proposal Category: GO Scientific Category: ISM ID: 8624 Title: Imaging and Spectroscopy of Dusty Circumstellar Disks PI: Alycia Weinberger PI Institution: University of California Los Angeles Understanding the properties and evolution of dusty disks in the circumstellar environments of young stars is a key element in furthering our concepts of the formation mechanisms of extra-solar planetary systems. In the past year, the advent of NICMOS and STIS coronagraphy has given rise to the first reflected light imaging, other than for Beta Pic, of dusty circumstellar disks with spatially resolved morphological structures. NICMOS has taken a first step in imaging these new disks, elucidating their geometries, morphologies, and bulk photometric properties, while increasing the number of such known systems from one to half a dozen. These dusty disks vary in physical size by over two orders of magnitude and exhibit radial anisotropies in their brightness distributions which may be indicative of dynamical confinement or sculpting of the disk particles by unseen planetary bodies. STIS follow-on imaging and spectroscopy are needed to provide further insight into the nature of the disk particles. With spectra, we will measure the albedo of the disk dust and search for complex molecules and water ice. With coronagraphic images, we will investigate the scattering phase function and hence the composition of the disk dust as well as measure the disk sizes and shapes with high precision. Such observations are of fundamental importance in establishing the physical basis for emergent theories of disk evolution and planet- building. ================================================================================ Proposal Category: GO Scientific Category: QAL ID: 8625 Title: The Metallicity of Gas in the Local Universe: Beyond the Milky Way PI: David V. Bowen PI Institution: Princeton Observatory We wish to obtain STIS spectra of three QSO/AGN which lie behind nearby galaxies, to measure the metallicity of the interstellar gas at the present epoch beyond the local group. We aim to provide the first steps in establishing a low-redshift anchor to the ever burgeoning abundance measurements of gas at high redshift, to quantify the range of abundances seen in the galaxies today, and thereby examine whether our galaxy might simply be metal rich in comparison. Our data will also provide valuable information for discriminating between competing models of galaxy evolution. The three probes are the best available for obtaining UV data with sufficient quality to reliably measure column densities and Doppler parameters; Q1219+047 passes 21 \h\ through the outer H I disk of M61, where there are no sites of current star formation; Mrk 205 shines through the inter-arm region of NGC 4319, and can be used to construct the first UV absorption-line atlas of a galaxy beyond the Magellanic Clouds; and Q1543+489 directly intercepts an intergalactic H I cloud associated with two nearby galaxies. In this latter case, direct measurement of the cloud's metallicity and hydrogen column density will also enable us to constrain the ionization parameter of the UV background radiation field. ================================================================================ Proposal Category: GO Scientific Category: QAL ID: 8626 Title: Spatially Resolved Spectroscopy of APM08279+5255 PI: Sara Ellison PI Institution: Institute of Astronomy We propose to obtain spatially resolved, high resolution spectra of the z=3.911 BAL quasar, APM 08279+5255. This ultra-luminous QSO is a triply imaged gravitationally lensed system with image separations of 0 nd38 -- 0 nd15. Ground-based observations of this bright source have revealed a rich absorption spectrum caused by both intervening material and the complex QSO environment and BAL flows. The proposed STIS spectrum, which will spatially resolve the individual quasar images, is a unique opportunity to probe the numerous intervening systems on sub-kpc scales, providing: o a sensitive probe of the structure of intervening galaxy halos and metal line systems on scales of ~ 0.2 -- 1.6 kpc h^-1, their kinematics and spatial extents, o multiple sightlines through the complex BAL flow on parsec scales, yielding information on ionization, kinematics and metal enrichment, We also request 5 orbits with WFPC2 in order to detect and measure the centroid of the lensing galaxy; this will provide the necessary information to remove the degeneracy in the present gravitational lensing models. ================================================================================ Proposal Category: GO Scientific Category: SF ID: 8627 Title: TESTING THEORIES OF WIND/JET PRODUCTION IN YSOs PI: Nuria Calvet PI Institution: Smithsonian Astrophysical Observatory We propose to use STIS ultraviolet spectroscopy to test theories of jet/wind production from the accretion disks of low-mass young stellar objects, providing new insight into disk physics, accretion energy balance, and jet collimation. STIS observations of the Fe II ultraviolet lines in absorption will probe lower-density and lower-temperature material than optical forbidden and permitted emission lines, and thus provide unique information on jet/wind launching and acceleration. Velocity-resolved spectra will distinguish between X-wind models, in which all the mass ejection occurs from the inner disk edge, and disk wind models, where the flow originates from a much larger area of the disk. Our results will provide important new constraints on the best-studied, best-understood astrophysical jet systems. ================================================================================ Proposal Category: GO Scientific Category: SF ID: 8628 Title: High Density (~ 10^9 cm^-3) gas in the jet formation region of T Tauri stars PI: Ana I. Gomez de Castro PI Institution: Instituto de Astronom'\ia y Geodesia Outflow is ubiquotous during star formation however the mechanism which drives it, is still uknown. The key observational information about how outflow is initiated is contained within a region of angular size smaller than 0.1 arcsec (for the nearest stars) which is not accessible to direct imaging. It has been shown that the jet density increases towards the source but the commonly used optical forbidden lines cannot probe densities higher than ~ 10^6 cm^-3. An analysis of the ultraviolet tracers of shocked material carried out by us and based on data from the HST Archive has shown that jet emission is also detected from the UV semiforbidden lines of C iii and Si iii . The infered electronic density of the emitting gas is ~ 10^9 - 10^10 cm^-3 ================================================================================ Proposal Category: GO Scientific Category: SP ID: 8629 Title: The Search for ``True'' Starburst Dust and the Importance of Metallicity on Properties of O & B Stars PI: Fred C. Bruhweiler PI Institution: The Catholic Univ. of America Much of what we know about starburst (SB) galaxies, at low and high redshift, depends upon the nature of the SB dust extinction and the intrinsic physical parameters of OB stars versus metallicity. Typically SBs, unlike our Galaxy, exhibit extinction laws with no 2200Angstrom\ peak. There is little information on the effects of dense star-formation on dust extinction properties. Specifically, no UV-visual extinction studies exist for the dense star-forming regions of 30 Dor (LMC) and NGC 346 (SMC), which represent prime laboratories for studying these effects. These regions have the highest concentration of young O stars in these galaxies, where 30 Dor is the nearest example of a definite starburst. Using the 2-D capability of STIS, we will a.) perform the first UV-visual extinction study of the dense regions of 30 Dor (in and around R136) and NGC 346, b.) produce unreddened OB star flux distributions in 30 Dor and NGC 346, c.) use these results to derive effective temperature, luminosity, and mass-loss rate correlations with spectral type and metallicity, and d.) explore if the extinction for the cores of 30 Dor and NGC 346 can be used to generate ``true'' starburst extinction laws. ================================================================================ Proposal Category: GO Scientific Category: SP ID: 8630 Title: The Deepest Far-UV Imaging Survey of Globular Clusters: NGC 6752 and NGC 6397 PI: Michael Shara PI Institution: American Museum of Natural History A few very close binaries can drive the dynamical evolution of an entire globular cluster. We propose the deepest UV imagery ever obtained on globular clusters to search for cataclysmic variables (CVs). CVs should be relatively easy to find in globular cores with HST, but there is a remarkable dearth of detected CVs in globular clusters relative to the large numbers predicted by tidal capture theory. This calls into serious doubt all of our understanding of globular cluster dynamical evolution. If most CVs in globular clusters are much fainter than canonical classical and dwarf novae, then tidal capture theory (and our claim to understand cluster evolution) can be salvaged. We propose to image the globular clusters NGC 6752 and NGC 6397 in the passband where CVs emit most of their radiation: the far UV, and at Lyalpha. Using the FUV-MAMA detector on STIS, we will reach an equivalent optical limiting magnitude of M_V = 13 at S/N=10 which is sensitive enough to detect even the faintest known CVs. If few or no faint CVs are found, then theorists will have run out of phase space and simple tidal capture theory will be shown to have made an incorrect prediction. This would force a major revision in our theory of tidal capture, and our understanding of globular cluster dynamical evolution. ================================================================================ Proposal Category: SNAP Scientific Category: AGN ID: 8631 Title: Bright Quasar Close Lensing Search II PI: Michael Gregg PI Institution: University of California, Davis enlargethispage0.25in We propose to expand our Cycle 8 second generation HST snapshot survey of bright quasars, optimized to find lenses with component image separations < 1". Most models of quasar lensing predict distributions which peak at separations in the range 0arcs5 to 1", yet the observed distribution of lenses peaks at 1arcs3. The lack of systems with close separations is difficult to reconcile with a flat universe, preferred by theory (inflation) and the observational determinations of the cosmological constant from type Ia supernovae. Our Cycle 8 survey improves over the earlier pre-refurbishment snapshot survey of quasars (Bahcall et al.\ 1992; Maoz et al.\ 1993) in several important respects. With the restored PSF and the image quality of STIS, the new images are considerably more sensitive to the presence of both close separation and faint lens components. Our snapshots are guided, multiple exposure observations, allowing a much better final data product. We are also obtaining exposures in both Clear and LongPass modes, providing immediate color information to gauge the chances that a pair of close images is consistent with lensing. At the time of this writing, about 80 of our 300 allocated snapshots have been taken. The early returns are exciting: we have one small (0arcs6) separation lens, plus 3 additional lens candidates at larger separations. Encouraged by these results, we propose to expand the survey in Cycle 9. ================================================================================ Proposal Category: SNAP Scientific Category: GAL ID: 8632 Title: A UV Atlas of Nearby Galaxies PI: Mauro Giavalisco PI Institution: Space Telescope Science Institute We propose a snapshot survey of local galaxies at UV wavelengths with WFPC2 and the F300W filter. The aim of the project is to build a reference UV Atlas of normal galaxies, whose optical images are well known, with the highest possible degree of information, covering all the morphological types and luminosity classes. The F300W passband is significantly bluer than the Johnson U, its transmittance is not limited by the atmosphere, and it offers adequate throughput for this project. The sample is extracted from the Revised Shapley- Ames Catalog and includes 130 galaxies with a redshift distribution centered around ~ 1500 km/sec and FWHM~ 500 km/s. At these redshifts the field-of-view of WFPC2 covers ~ 23 kpc, or approximately the Holmberg diameter of a large spiral galaxy. No systematic imaging of local galaxies at wavelengths bluer than the B band are currently available and the general properties of the various Hubble types in the UV are essentially unknown. Still, this information is crucial for a variety of studies, which include star-formation activity and evolution, nuclear activity, the physics of the ISM, the evolution of galaxy morphology. The WFPC2 UV Atlas will provide a unique reference data set which will be valuable for a wide variety of future observations, both ground--based and with HST. This project is a service to the community, and we waive the proprietary period. ================================================================================ Proposal Category: SNAP Scientific Category: HS ID: 8633 Title: The Physical Parameters of the Hottest, Most Luminous Stars as a Function of Metallicity PI: Philip Massey PI Institution: National Optical Astronomy Observatories 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, and compare these to the extensive data that exists for higher metallicity Galactic stars. What we lack is knowledge of 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 six of our stars for which nebular contamination is significant even with long -slit subtraction in out ground-based data. These new HST data will allow us to understand how the spectral type to effective temperatures depend upon metallicity (necessary in determining IMFs), as well as allow us to explore the astrophysically interesting regime of stars of extreme temperatures, masses and luminosities. Together with the optical data, they will also provide important information about the strengths of stellar winds at extreme luminosities and the calibration of the Wind Momentum - Luminosity Relationship at lower metallicities. ================================================================================ Proposal Category: SNAP Scientific Category: SS ID: 8634 Title: Atmospheric Variability on Uranus and Neptune PI: Kathy Rages PI Institution: Space Physics Research Institute/NASA Ames Research Center We propose snapshot observations of Uranus and Neptune to monitor changes in their atmospheres on time scales of months to years. Uranus is rapidly approaching equinox in 2007, with another 4degrees\ of latitude in the northern hemisphere becoming visible every year. Recent HST images during this unique epoch (6818: Hammel, Lockwood, and Rages; 7429: Tomasko and Karkoschka; 7885: Hammel, Karkoschka, and Marley) have revealed: (i) strongly wavelength-dependent latitudinal structure, (ii) the presence of numerous visible-wavelength cloud features in the northern hemisphere, and, (iii) in the near-IR, discrete features northward of 25degrees N that have the highest contrast ever seen for a Uranian cloud (Karkoschka 1998c; Hammel et al.\ 1999). Long-term ground- based observations (Lockwood and Thompson 1999) show seasonal brightness changes whose origins are not well understood. Recent IR images of Neptune (http://www2.keck.hawaii.edu:3636/realpublic/ao/neptune.html) obtained using adaptive optics on the Keck Telescope indicate that a new ``Bright Companion" type of feature has recently appeared in the southern hemisphere. Snapshot observations of these two dynamic planets can supply context in which to discern the nature of long-term changes in their latitudinal atmospheric bands and to track the appearance, movement, and disappearance of discrete albedo features. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8635 Title: A test of pulsation and diffusion theory for subluminous B stars PI: Ulrich Heber PI Institution: Dr. Remeis-Sternwarte The recent discovery of radial and nonradial mode pulsations in nearly 20 sdB stars makes it possible to use asteroseismology to probe the internal structure of these stars and discern their evolutionary status; this is needed for reasons as diverse as understanding the late stages of stellar evolution and the calibration of the observed ultraviolet upturn in giant elliptical galaxies as an age indicator. Central to any asteroseismological study is an identification of the pulsation driving mechanism; evidence to date suggests that this is due to the recently discovered heavy metal opacity. The necessary metal abundance has to be maintained by diffusive equilibrium between gravitational settling and radiative levitation. Abundance analyses of high resolution optical spectra have, however, revealed that the surface iron abundance is not discriminating between pulsating and non-pulsating sdB stars. We propose to extend the abundance analyses of three pulsating sdB stars and two non-pulsating sdB stars to chemical elements unobservable from the ground using echelle UV spectra; this would enable diffusion/pulsation calculations to be tested by searching for significant differences in their surface abundance patterns. The targets are chosen to cover the full range of sdB gravities since \logg\ is the dominant parameter for both diffusion and pulsation. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8636 Title: Metal abundances in very hot DA white dwarfs -- a test of diffusion theory PI: Ralf Napiwotzki PI Institution: Dr. Remeis-Sternwarte The photospheric abundances of white dwarfs are controlled by diffusion processes like gravitational settling and radiative levitation. UV, EUV and X- ray observations revealed a large metallicity spread from star to star, which cannot be explained by state-of-the-art stationary diffusion calculations. Additional processes, e.g. a weak stellar wind, have been invoked. A contrasting pair of extremely hot DA white dwarfs, recently discovered by the HS survey, has very similar temperature and gravity, but probably very different metal abundances. HS 0505+0112 is unique because it is the only H- rich hot white dwarf known to show optical C lines. Balmer line fitting yields further evidence that the heavy element abundances of HS0505+0112 must be high. In contrast HS 0615+6535 displays Balmer lines only and fitting their line profiles is consistent with an unusually low amount of metals. We propose to determine abundances of C,N,O,Si and Fe and Ni directly from STIS UV spectra by means of fully metal line blanketed NLTE model atmospheres. Indications of mass loss will also be searched for providing us with an important check of the diffusion theory in white dwarfs. Both stars are also ideally suited for a test, whether the C, N, O line opacity can account for the Balmer line discrepancy noted for the analysis of very hot H-rich stars. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8637 Title: Distance to the prototype WD showing signatures of a super-hot wind PI: Klaus Werner PI Institution: Universitaet Tuebingen, Institut fuer Astronomie und Astrophysik We propose to determine the distance to the prototype of a new class of hot white dwarfs (WD). Their optical spectra reveal absorption lines from ultra- high ionized metals (e.g.\ IonOVIII), a phenomenon never observed before in any astronomical object. The occurrence of such features requires temperatures in the order of 10^6 K, far in excess of the stellar T_ eff. The asymmetric line profiles suggest formation in a rapidly accelerating high-speed wind (10,000 km s^-1). These stars represent the most convincing proof for on-going mass-loss from WDs. We have demonstrated that a large fraction of hot WDs shows this phenomenon, concluding that perhaps all WD go through this evolutionary stage. For the prototype we will determine stellar parameters and possible consequences of the mass-loss for WD evolution on hand of detailed NLTE modeling. The distance to the star is an essential prerequisite for this. We propose to derive the distance spectroscopically by determination of spectral type and luminosity class of the cool companion of the WD. ================================================================================ Proposal Category: GO Scientific Category: HS ID: 8638 Title: Temperature scale and metal abundances of hot hydrogen- rich central stars of planetary nebulae PI: Klaus Werner PI Institution: Universitaet Tuebingen, Institut fuer Astronomie und Astrophysik We propose UV spectroscopy of a sample of hot hydrogen-rich central stars of PNe, covering the hottest phase of post-AGB evolution (T_ eff>70 000 K). The spectra shall be analyzed with fully metal line blanketed NLTE model atmospheres in order to determine T_ eff, surface gravity, and chemical composition. The results will address the following problems: 1. The temperature scale of the hottest central stars is poorly known. Iron lines, only accessible in the UV, are ideal temperature indicators to set up a reliable temperature scale. 2. Depending on the particular star, the derived metal abundances are either dominated by current diffusion processes or they originate from dredge-up phases during previous AGB evolution. We expect that our sample comprises different objects so that both processes/phases can be studied in detail. 2a. Those objects, which show qualitatively a metal abundance pattern which points at dredge-up phases, can be used to quantitatively check against abundance predictions of stellar evolution theory. 2b. The other objects, where gravitational diffusion and radiative acceleration determine the photospheric metal abundances, will be used to check our NLTE models which for the first time include diffusion processes self-consistently. ================================================================================ Proposal Category: GO Scientific Category: AGN ID: 8639 Title: The Origin of Gaseous Outflows in Active Galaxies PI: Andrew Wilson PI Institution: University of Maryland We have recently obtained HST PC images of the ionized gas in the Circinus galaxy, a nearby (distance 4 Mpc) Seyfert 2. The images reveal that the nuclear (i.e. the inner 2^ = 40 pc) high excitation gas is ``V-shaped'' and represents the inner part of the ``ionization cone'' seen previously on much larger scales in ground-based observations. At 10 - 15^ = 190 - 280 pc from the nucleus, there is an elliptical ring of high excitation gas, which we infer to be the end of the intrinsically circular cone viewed at its known orientation. The images thus suggest that the observed emission lies along the boundary of a conical structure, a situation which has probably originated through mass entrainment of dense gas in the galaxy disk along the edges of a low density outflow. We wish to obtain long slit observations of this structure. Our goals are: 1) to confirm or reject this picture kinematically; 2) investigate how gas is entrained into the outflow from the dense ism in the galaxy disk in the inner (< 40 pc) region of the outflow at unprecedented spatial resolution for a Seyfert galaxy (our resolution of 1 pc is comparable to or smaller than the expected radius of the inner edge of the putative blocking ``torus''); 3) distinguish between collimation of ionization photons or of gaseous outflow as the origin of the ``ionization cone''; 4) attempt to measure the mass of the nuclear black hole using a long slit spectrum of the disk HII regions. ================================================================================ Proposal Category: GO Scientific Category: COS ID: 8640 Title: A Public STIS Survey of the Host Galaxies of Gamma-Ray Bursts PI: Stephen Holland PI Institution: University of Aarhus We propose to obtain high-resolution STIS images of the fields containing every gamma-ray burst with well-localized coordinates; i.e.\ the burst has been localized to within ~ 1". The goal of this survey is to obtain a uniform sample of images of the host galaxies of these bursts. This data will be used to search for host galaxies that are too faint to be discovered by ground- based searches, to study the morphology of host galaxies, and to compare the population of galaxies that contain gamma-ray bursts to other populations of galaxies such as Lym