We propose to image the north east quadrant of M31 to deep limits in the UV, optical, and near-IR. HST imaging should resolve the galaxy into more than 100 million stars, all with common distances and foreground extinctions. UV through NIR stellar photometry (F275W, F336W with WFC3/UVIS, F475W and F814W with ACS/WFC, and F110W and F160W with WFC3/NIR) will provide effective temperatures for a wide range of spectral types, while simultaneously mapping M31's extinction. Our central science drivers are to: understand high-mass variations in the stellar IMF as a function of SFR intensity and metallicity; capture the spatially-resolved star formation history of M31; study a vast sample of stellar clusters with a range of ages and metallicities. These are central to understanding stellar evolution and clustered star formation; constraining ISM energetics; and understanding the counterparts and environments of transient objects (novae, SNe, variable stars, x-ray sources, etc.). As its legacy, this survey adds M31 to the Milky Way and Magellanic Clouds as a fundamental calibrator of stellar evolution and star-formation processes for understanding the stellar populations of distant galaxies. Effective exposure times are 977s in F275W, 1368s in F336W, 4040s in F475W, 4042s in F814W, 699s in F110W, and 1796s in F160W, including short exposures to avoid saturation of bright sources. These depths will produce photon-limited images in the UV. Images will be crowding-limited in the optical and NIR, but will reach below the red clump at all radii. The images will reach the Nyquist sampling limit in F160W, F475W, and F814W.
COS FUV DCE Memory Dump
Whenever the FUV detector high voltage is on, count rate and current draw information is collected, monitored, and saved to DCE memory. Every 10 msec the detector samples the currents from the HV power supplies (HVIA, HVIB) and the AUX power supply (AUXI). The last 1000 samples are saved in memory, along with a histogram of the number of occurrences of each current value.
In the case of a HV transient (known as a "crackle" on FUSE), where one of these currents exceeds a preset threshold for a persistence time, the HV will shut down, and the DCE memory will be dumped and examined as part of the recovery procedure. However, if the current exceeds the threshold for less than the persistence time (a "mini-crackle" in FUSE parlance), there is no way to know without dumping DCE memory. By dumping and examining the histograms regularly, we will be able to monitor any changes in the rate of "mini-crackles" and thus learn something about the state of the detector.
Primordial formation of Close Binaries in Globular Clusters with Low Density Cores
The primordial binary population is a key input parameter for any realistic model of dense star cluster dynamics. However, the number of primordial binaries and its direct implications for the formation rate of close binaries remain poorly understood. Theoretical calculations show that cataclysmic variables can be formed directly from primordial binaries in or near the core of low core density globular clusters. We propose to use Chandra/HST to study low density core globular clusters systematically and to test the prediction that low-luminosity X-ray sources can be formed from primordial binaries in the cluster core. This project will complement our successful Chandra/HST program to study the dynamical formation of X-ray sources in high core density globular clusters.
CCD Daily Monitor (Part 3)
This program comprises basic tests for measuring the read noise and dark current of the ACS WFC and for tracking the growth of hot pixels. The recorded frames are used to create bias and dark reference images for science data reduction and calibration. This program will be executed four days per week (Mon, Wed, Fri, Sun) for the duration of Cycle 17. To facilitate scheduling, this program is split into three proposals. This proposal covers 308 orbits (19.25 weeks) from 21 June 2010 to 1 November 2010.
IR Dark Current Monitor
Analyses of ground test data showed that dark current signals are more reliably removed from science data using darks taken with the same exposure sequences as the science data, than with a single dark current image scaled by desired exposure time. Therefore, dark current images must be collected using all sample sequences that will be used in science observations. These observations will be used to monitor changes in the dark current of the WFC3-IR channel on a day-to-day basis, and to build calibration dark current ramps for each of the sample sequences to be used by Gos in Cycle 17. For each sample sequence/array size combination, a median ramp will be created and delivered to the calibration database system (CDBS).
Cycle 17: UVIS Bowtie Monitor
Ground testing revealed an intermittent hysteresis type effect in the UVIS detector (both CCDs) at the level of ~1%, lasting hours to days. Initially found via an unexpected bowtie-shaped feature in flatfield ratios, subsequent lab tests on similar e2v devices have since shown that it is also present as simply an overall offset across the entire CCD, i.e., a QE offset without any discernable pattern. These lab tests have further revealed that overexposing the detector to count levels several times full well fills the traps and effectively neutralizes the bowtie. Each visit in this proposal acquires a set of three 3x3 binned internal flatfields: the first unsaturated image will be used to detect any bowtie, the second, highly exposed image will neutralize the bowtie if it is present, and the final image will allow for verification that the bowtie is gone.
UVIS Cycle 17 Contamination Monitor
The UV throughput of WFC3 during Cycle 17 is monitored via weekly standard star observations in a subset of key filters covering 200-600nm and F606W, F814W as controls on the red end. The data will provide a measure of throughput levels as a function of time and wavelength, allowing for detection of the presence of possible contaminants.
WFC3 UVIS CCD Daily Monitor
The behavior of the WFC3 UVIS CCD will be monitored daily with a set of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K subarray biases are acquired at less frequent intervals throughout the cycle to support subarray science observations. The internals from this proposal, along with those from the anneal procedure (Proposal 11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS).
CCD Bias Monitor-Part 2
Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1, and 1x1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns.
CCD Dark Monitor Part 2
Monitor the darks for the STIS CCD.
Is 47 Tuc Young? Measuring its White Dwarf Cooling Age and Completing a Hubble Legacy
With this proposal we will firmly establish the age of 47 Tuc from its cooling white dwarfs. 47 Tuc is the nearest and least reddened of the metal-rich disk globular clusters. It is also the template used for studying the giant branches of nearby resolved galaxies. In addition, the age sensitive magnitude spread between the main sequence turnoff and horizontal branch is identical for 47 Tuc, two bulge globular clusters and the bulge field population. A precise relative age constraint for 47 Tuc, compared to the halo clusters M4 and NGC 6397, both of which we recently dated via white dwarf cooling, would therefore constrain when the bulge formed relative to the old halo globular clusters. Of particular interest is that with the higher quality ACS data on NGC 6397, we are now capable with the technique of white dwarf cooling of determining ages to an accuracy of +/-0.4 Gyrs at the 95% confidence level. Ages derived from the cluster turnoff are not currently capable of reaching this precision. The important role that 47 Tuc plays in galaxy formation studies, and as the metal-rich template for the globular clusters, makes the case for a white dwarf cooling age for this metal-rich cluster compelling.
Several recent analyses have suggested that 47 Tuc is more than 2 Gyrs younger than the Galactic halo. Others have suggested an age similar to that of the most metal poor globular clusters. The current situation is clearly uncertain and obviously a new approach to age dating this important cluster is required.
With the observations of 47 Tuc, this project will complete a legacy for HST. It will be the third globular cluster observed for white dwarf cooling; the three covering almost the full metallicity range of the cluster system. Unless JWST has its proposed bluer filters (700 and 900 nm) this science will not be possible perhaps for decades until a large optical telescope is again in space. Ages for globular clusters from the main sequence turnoff are less precise than those from white dwarf cooling making the science with the current proposal truly urgent.
Kinematic Reconstruction of the Origin and IMF of the Massive Young Clusters at the Galactic Center
We propose to exploit the wide field capabilities of Wide Field Camera 3 to study star formation at the Galactic center. By studying young stars located in the most physically extreme region of our Galaxy, we can test star formation theories, which suggest that such environments should favor high mass stars and, in extreme cases, should suppress star formation entirely. Specifically, we will measure the proper motions and photometry of stars over the full extent of the three massive young clusters that have been identified at the Galactic Center (Arches, Quintuplet, and the Young Nuclear Star Cluster). These observations are a factor of ?2000 more efficient than what can be done with ground-based adaptive optics. Our goals are two-fold. First, we hope to establish the initial sites of star formation in order to obtain an accurate estimate of the conditions that led to the stellar populations within these clusters. Answering this question for the Young Nuclear Star Cluster is particularly important as it establishes whether or not star formation can indeed proceed within 0.1 pc of our Galaxy's supermassive black hole. Second, we will measure the IMF in the Arches and Quintuplet, where dynamical evolution is less severe, using proper motions to determine membership and to reveal the tidal radius. Probing how the properties of the emergent stellar populations within our Galaxy may be affected by the physical environment in which they arise is an important first step to understanding how they might vary as a function of cosmic time and thereby affect our models of galaxy formation and evolution.
The Host Environments of Type Ia Supernovae in the SDSS Survey
The Sloan Digital Sky Survey Supernova Survey has discovered nearly 500 type Ia supernovae and created a large, unique, and uniform sample of these cosmological tools. As part of a comprehensive study of the supernova hosts, we propose to obtain Hubble ACS images of a large fraction of these galaxies. Integrated colors and spectra will be measured from the ground, but we require high-resolution HST imaging to provide accurate morphologies and color information at the site of the explosion. This information is essential in determining the systematic effects of population age on type Ia supernova luminosities and improving their reliability in measuring dark energy. Recent studies suggest two populations of type Ia supernovae: a class that explodes promptly after star-formation and one that is delayed by billions of years. Measuring the star-formation rate at the site of the supernova from colors in the HST images may be the best way to differentiate between these classes.
A Dynamical-Compositional Survey of the Kuiper Belt: A New Window Into the Formation of the Outer Solar System
The eight planets overwhelmingly dominate the solar system by mass, but their small numbers, coupled with their stochastic pasts, make it impossible to construct a unique formation history from the dynamical or compositional characteristics of them alone. In contrast, the huge numbers of small bodies scattered throughout and even beyond the planets, while insignificant by mass, provide an almost unlimited number of probes of the statistical conditions, history, and interactions in the solar system. To date, attempts to understand the formation and evolution of the Kuiper Belt have largely been dynamical simulations where a hypothesized starting condition is evolved under the gravitational influence of the early giant planets and an attempt is made to reproduce the current observed populations. With little compositional information known for the real Kuiper Belt, the test particles in the simulation are free to have any formation location and history as long as they end at the correct point. Allowing compositional information to guide and constrain the formation, thermal, and collisional histories of these objects would add an entire new dimension to our understanding of the evolution of the outer solar system. While ground based compositional studies have hit their flux limits already with only a few objects sampled, we propose to exploit the new capabilities of WFC3 to perform the first ever large-scale dynamical-compositional study of Kuiper Belt Objects (KBOs) and their progeny to study the chemical, dynamical, and collisional history of the region of the giant planets. The sensitivity of the WFC3 observations will allow us to go up to two magnitudes deeper than our ground based studies, allowing us the capability of optimally selecting a target list for a large survey rather than simply taking the few objects that can be measured, as we have had to do to date. We have carefully constructed a sample of 120 objects which provides both overall breadth, for a general understanding of these objects, plus a large enough number of objects in the individual dynamical subclass to allow detailed comparison between and within these groups. These objects will likely define the core Kuiper Belt compositional sample for years to come. While we have many specific results anticipated to come from this survey, as with any project where the field is rich, our current knowledge level is low, and a new instrument suddenly appears which can exploit vastly larger segments of the population, the potential for discovery -- both anticipated and not -- is extraordinary.
Binary Brown Dwarfs and the L/T Transition
Brown dwarfs traverse spectral types M, L and T as their atmospheric structure evolves and they cool into oblivion. This SNAPSHOT program will obtain WFC3-IR images of 45 nearby late-L and early-T dwarfs to investigate the nature of the L/T transition. Recent analyses have suggested that a substantial proportion of late-L and early-T dwarfs are binaries, comprised of an L dwarf primary and T dwarf secondary. WFC3-IR observations will let us quantify this suggestion by expanding coverage to a much larger sample, and permitting comparison of the L/T binary fraction against ?normal? ultracool dwarfs. Only eight L/T binaries are currently known, including several that are poorly resolved: we anticipate at least doubling the number of resolved systems. The photometric characteristics of additional resolved systems will be crucial to constraining theoretical models of these late-type ultracool dwarfs. Finally, our data will also be eminently suited to searching for extremely low luminosity companions, potentially even reaching the Y dwarf regime.
The Nuclear Structure of OH Megamaser Galaxies
We propose a snapshot survey of a complete sample of 80 OH megamaser galaxies. Each galaxy will be imaged with the ACS/WFC through F814W and a linear ramp filter (FR656N or FR716N or FR782N or FR853N) allowing us to study both the spheroid and the gas morphology in Halpha + [N II]. We will use the 9% ramps FR647M (5370-7570 angstroms) centered at 7000 angstroms and FR914M (7570-10, 719 angstroms) 8000 angstroms for continuum subtraction for the high and low z objects respectively. OH megamaser galaxies (OHMG) form an important class of ultraluminous IR-galaxies (ULIRGs) whose maser lines emit QSO-like luminosities. ULIRGs in general are associated with recent mergers but it is often unclear whether their power output is dominated by starbursts or a hidden QSO because of the high absorbing columns which hide their nuclei even at X-ray wavelengths. In contrast, OHMG exhibit strong evidence for the presence of an energetically important and recently triggered active nucleus. In particular it is clear that much of the gas must have already collapsed to form a nuclear disk which may be the progenitor of a circum-nuclear torus, a key element of the unified scheme of AGN. A great advantage of studying OHMG systems over the general ULIRG population, is that the circum-nuclear disks are effectively "fixed" at an inner, edge on, orientation, eliminating varying inclination as a nuisance parameter. We will use the HST observations in conjunction with existing maser and spectroscopic data to construct a detailed picture of the circum-nuclear regions of a hitherto relatively neglected class of galaxy that may hold the key to understanding the relationship between galaxy mergers, nuclear star-formation, and the growth of massive black holes and the triggering of nuclear activity.
Spectroscopy of IR-Selected Galaxy Clusters at 1 < z < 1.5
We propose to obtain WFC3 G141 and G102 slitless spectroscopy of galaxy clusters at 1 < z < 1.5 that were selected from the IRAC survey of the Bootes NDWFS field. Our IRAC survey contains the largest sample of spectroscopically confirmed clusters at z > 1. The WFC3 grism data will measure H-alpha to determine SFR, and fit models to the low resolution continua to determine stellar population histories for the brighter cluster members, and redshifts for the red galaxies too faint for ground-based optical spectroscopy.
Characterizing Atmospheric Sodium in the Transiting Hot-Jupiter HD189733b
We propose STIS transit observations of the exoplanet HD189733b with the goal of measuring atmospheric atomic sodium. Our strategy is to repeat the observing methods used for HD209458b, which resulted in a successful exoplanetary atmospheric sodium detection. Initial ground-based measurements suggest that the sodium signature on HD189733 could be up to three times larger than HD209458b, making a robust 8 detection possible within a 12 orbit program observing three transits. Transit transmission spectra resulting from space-based measurements have the advantage of retaining absolute transit depths when features are measured, which will make it possible to provide an observational link between sodium and atmospheric haze detected with ACS. Such a link can break modeling degeneracies and providing stringent constraints on the overall atmospheric properties, making such atmospheric information as abundances and the temperature-pressure-altitude relation known. A successful measurement will also allow for comparative atmospheric exoplanetology, as an atmospheric feature will be measured with the same instrument in two separate planets.
Galaxies at z~7-10 in the Reionization Epoch: Luminosity Functions to <0.2L* from Deep IR Imaging of the HUDF and HUDF05 Fields
The first generations of galaxies were assembled around redshifts z~7-10+, just 500-800 Myr after recombination, in the heart of the reionization of the universe. We know very little about galaxies in this period. Despite great effort with HST and other telescopes, less than ~15 galaxies have been reliably detected so far at z>7, contrasting with the ~1000 galaxies detected to date at z~6, just 200-400 Myr later, near the end of the reionization epoch. WFC3 IR can dramatically change this situation, enabling derivation of the galaxy luminosity function and its shape at z~7-8 to well below L*, measurement of the UV luminosity density at z~7-8 and z~8-9, and estimates of the contribution of galaxies to reionization at these epochs, as well as characterization of their properties (sizes, structure, colors). A quantitative leap in our understanding of early galaxies, and the timescales of their buildup, requires a total sample of ~100 galaxies at z~7-8 to ~29 AB mag. We can achieve this with 192 WFC3 IR orbits on three disjoint fields (minimizing cosmic variance): the HUDF and the two nearby deep fields of the HUDF05. Our program uses three WFC3 IR filters, and leverages over 600 orbits of existing ACS data, to identify, with low contamination, a large sample of over 100 objects at z~7-8, a very useful sample of ~23 at z~8-9, and limits at z~10. By careful placement of the WFC3 IR and parallel ACS pointings, we also enhance the optical ACS imaging on the HUDF and a HUDF05 field. We stress (1) the need to go deep, which is paramount to define L*, the shape, and the slope alpha of the luminosity function (LF) at these high redshifts; and (2) the far superior performance of our strategy, compared with the use of strong lensing clusters, in detecting significant samples of faint z~7-8 galaxies to derive their luminosity function and UV ionizing flux. Our recent z~7.4 NICMOS results show that wide-area IR surveys, even of GOODS-like depth, simply do not reach faint enough at z~7-9 to meet the LF and UV flux objectives. In the spirit of the HDF and the HUDF, we will waive any proprietary period, and will also deliver the reduced data to STScI. The proposed data will provide a Legacy resource of great value for a wide range of archival science investigations of galaxies at redshifts z~2-9. The data are likely to remain the deepest IR/optical images until JWST is launched, and will provide sources for spectroscopic follow up by JWST, ALMA and EVLA.
The Nature of Low-Ionization BAL QSOs
The rare subclass of optically-selected QSOs known as low-ionization broad absorption line (LoBAL) QSOs show signs of high-velocity gas outflows and reddened continua indicative of dust obscuration. Recent studies show that galaxies hosting LoBAL QSOs tend to be ultraluminous infrared systems that are undergoing mergers, and that have dominant young (< 100 Myr) stellar populations. Such studies support the idea that LoBAL QSOs represent a short- lived phase early in the life of QSOs, when powerful AGN-driven winds are blowing away the dust and gas surrounding the QSO. If so, understanding LoBALs would be critical in the study of phenomena regulating black hole and galaxy evolution, such as AGN feedback and the early stages of nuclear accretion. These results, however, come from very small samples that may have serious selection biases. We are therefore taking a more aggressive approach by conducting a systematic multiwavelength study of a volume limited sample of LoBAL QSOs at 0.5 < z < 0.6 drawn from SDSS. We propose to image their host galaxies in two bands using WFC3/UVIS and WFC3/IR to study the morphologies for signs of recent tidal interactions and to map their interaction and star forming histories. We will thus determine whether LoBAL QSOs are truly exclusively found in young merging systems that are likely to be in the early stages of nuclear accretion.
Investigations of the Pluto System
We propose a set of high SNR observations of the Pluto system that will provide improved lightcurves, orbits, and photometric properties of Nix and Hydra. The key photometric result for Nix and Hydra will be a vastly improved lightcurve shape and rotation period to test if the objects are in synchronous rotation or not. A second goal of this program will be to retrieve a new epoch of albedo map for the surface of Pluto. These observations will also improve masses and in some case densities for the bodies in the Pluto system.
COS-GTO: Star Formation/Lyman-Alpha
A sample of 20 star-forming galaxies will be observed with COS G130M. The galaxies were selected from the Kitt Peak International Spectroscopic Survey (KISSR) data release and cover a broad range of luminosity, oxygen abundance, and reddening. The goal of the program is to characterize the Lyman-alpha properties and establish correlations with fundamental galaxy properties. Each galaxy will be observed for one orbit.
Characterizing the Stellar Populations in Lyman-Alpha Emitters and Lyman Break Galaxies at 5.7< z<7 in the Subaru Deep Field
The epoch of reionization marks a major phase transition of the Universe, during which the intergalactic space became transparent to UV photons. Determining when this occurred and the physical processes involved represents the latest frontier in observational cosmology. Over the last few years, searches have intensified to identify the population of high-redshift (z>6) galaxies that might be responsible for this process, but the progress is hampered partly by the difficulty of obtaining physical information (stellar mass, age, star formation rate/history) for individual sources. This is because the number of z>6 galaxies that have both secure spectroscopic redshifts and high-quality infrared photometry (especially with Spitzer/IRAC) is still fairly small. Considering that only several photometric points are available per source, and that many model SEDs are highly degenerate, it is crucial to obtain as many observational constraints as possible for each source to ensure the validity of SED modeling. To better understand the physical properties of high-redshift galaxies, we propose here to conduct HST/NICMOS (72 orbits) and Spitzer/IRAC (102 hours) imaging of spectroscopically confirmed, bright (z<26 mag (AB)) Ly-alpha emitters (LAEs) and Lyman-break galaxies (LBGs) at 5.7< z<7 selected from the Subaru Deep Field. Spectroscopic redshifts remove one critical free parameter from SED modeling while bright source magnitudes ensure high-quality photometric data. By making accurate determinations of stellar masses, ages, and star-formation histories, we will specifically address the following major questions: (1) Do LAEs and LBGs represent physically different galaxy populations at z>6 as suggested recently? (2) Is Ly-alpha emission systematically suppressed at z>6 with respect to continuum emission? (i.e., are we reaching the epoch of incomplete reionization?), and (3) Do we see any sign of abnormally young stellar population in any of the z>6 galaxies?