Imaging the Crab Nebula while it is Flaring in Gamma-rays
The high energy gamma-ray flux from the Crab nebula doubled in a couple of days (from September 19 to September 21). Such enhancement, never seen before, is clearly detected both by Agile and Fermi, the two gamma-ray telescopes currently in operation. While such huge brightening is exciting the entire astrophysical community, TOOs are being scheduled by high energy space observatories such as Integral, Swift and Chandra. By imaging the status of the knots and wisps in the inner Crab nebula, HST could provide a unique piece of information, which may yield a clue to understand the source behavior.
WFC3/UVIS Charge Injection Test
In preparation for making charge injection (CI) available to observers, this proposal will 1) confirm that the CI performs on-orbit as it did on the ground, 2) provide an initial assessment of which CI mode is most effective (10, 17, 25 line or continuous), and 3) obtain a baseline calibration for each mode.
LARS - The Lyman Alpha Reference Sample
Lyman-alpha (Lya) is intrinsically the strongest recombination line in HII nebulae, reprocessing around 1/3 of the ionizing energy. This fact, combined with a rest wavelength that makes it convenient for high redshift studies have made Lya the dominant spectral probe of galaxy formation and evolution in the distant universe. At the same time, our understanding of emission and escape from galaxies is extremely patchy, for two reasons: 1) The resonant nature of Lya makes radiative transfer effects very important, and 2) with a rest wavelength pretty far out in the ultra violet (UV), detailed studies of local galaxies are difficult and require space instrumentation. In contrast to the thousands of galaxies in the nearby universe that have been studied at high spatial resolution (through ground based telescopes and yet a little further with HST) in optical broad bands and emission lines like H-alpha, only six (sic!) galaxies have Lya imaging available.
The Lya images available so far indicate that when Lya escapes, it does so primarily through a low surface brightness resonantly scattered component. With this proposal, we aim at observing 14 new targets and thereby increase the number of high resolution Lya images to 20, for a UV and H-alpha selected sample. By utilizing an alternative observational approach we will also improve the quality of the images by an order of magnitude. A better physical understanding of how Lya photons travel through and escape from galaxies is vital for interpreting and understanding observations at high redshifts, and would be an important legacy of HST in the JWST and ELT era, when the high-resolution UV imaging window on the Universe has been closed.
A public SNAPSHOT Survey of Gamma-ray Burst Host Galaxies
We propose to conduct a public infrared survey of the host galaxies of Swift selected gamma-ray bursts (GRBs) at z<3. By obtaining deep, diffraction limited imaging in the IR we will complete detections for the host galaxies, and in concert with our extensive ground based afterglow and host programmes will compile a detailed catalog of the properties of high-z galaxies selected by GRBs. In particular these observations will enable us to study the colours, luminosities and morphologies of the galaxies. This in turn informs studies of the nature of the progenitors and the role of GRBs as probes of star formation across cosmic history. Ultimately it provides a product of legacy value which will greatly complement further studies with next generation facilities such as ALMA and JWST.
How Dwarf Galaxies Got That Way: Mapping Multiphase Gaseous Halos and Galactic Winds Below L*
One of the most vexing problems in galaxy formation concerns how gas accretion and feedback influence the evolution of galaxies. In high mass galaxies, numerical simulations predict the initial fuel is accreted through 'cold' streams, after which AGN suppress star formation to leave galaxies red and gas-poor. In the shallow potential wells that host dwarf galaxies, gas accretion can be very efficient, and "superwinds" driven either by hot gas expelled by SNe or momentum imparted by SNe and hot-star radiation are regarded as the likely source(s) of feedback. However, major doubts persist about the physics of gas accretion, and particularly about SN-driven feedback, including their scalings with halo mass and their influence on the evolution of the galaxies. While "superwinds" are visible in X-rays near the point of their departure, they generally drop below detectable surface-brightness limits at ~ 10 kpc. Cold clumps in winds can be detected as blue-shifted absorption against the galaxy's own starlight, but the radial extent of these winds are difficult to constrain, leaving their energy, momentum, and ultimate fate uncertain. Wind prescriptions in hydrodynamical simulations are uncertain and at present are constrained only by indirect observations, e.g. by their influence on the stellar masses of galaxies and IGM metallicity. All these doubts lead to one conclusion: we do not understand gas accretion and feedback because we generally do not observe the infall and winds directly, in the extended gaseous halos of galaxies, when it is happening. To do this effectively, we must harness the power of absorption-line spectroscopy to measure the density, temperature, metallicity, and kinematics of small quantities of diffuse gas in galaxy halos. The most important physical diagnostics lie in the FUV, so this is uniquely a problem for HST and COS. We propose new COS G130M and G160M observations of 41 QSOs that probe the gaseous halos of 44 SDSS dwarf galaxies well inside their virial radii. Using sensitive absorption-line measurements of the multiphase gas diagnostics Lya, CII/IV, Si II/III/IV, and other species, supplemented by optical data from SDSS and Keck, we will map the halos of galaxies with L = 0.02 - 0.3 L*, stellar masses M* = 10^(8-10) Msun, over impact parameter from 15 - 150 kpc. These observations will directly constrain the content and kinematics of accreting and outflowing material, provide a concrete target for simulations to hit, and statistically test proposed galactic superwind models. These observations will also inform the study of galaxies at high z, where the shallow halo potentials that host dwarf galaxies today were the norm. These observations are low-risk and routine for COS, easily schedulable, and promise a major advance in our understanding of how dwarf galaxies came to be.
HST U-band Survey of Star Clusters in Nearby Star-Forming Galaxies
We propose a small Snapshot program to obtain U-band imaging of a sample of 22 nearby star-forming galaxies with existing HST B, V, and I-band imaging. With the high UV efficiency and large field of view of WFC3/UVIS, it is now possible to obtain deep U-band imaging for a large sample of galaxies, and address fundamental questions on the cluster systems which can only now be answered. We will focus mainly on the young stellar cluster populations of these galaxies and use the deep U-band observations to accurately age date tens or even hundreds of clusters in each galaxy. By measuring the ages and masses of the cluster populations, we will be able to answer many of the outstanding questions regarding their properties, survival rates, cluster formation histories and environmental dependencies. The overall aim will be to relate cluster formation and cluster properties to the star formation rates and morphologies of their host galaxies. In particular, this dataset will be used to: 1) constrain the fraction of stars that form in clusters and search for environmental dependencies; 2) study the cluster luminosity/mass function and determine if a characteristic mass exists in the distribution; 3) measure the size (radius) distribution of the clusters and determine if this has a dependence on environment; 4) empirically constrain cluster disruption laws; and 5) determine the star/cluster formation histories of these galaxies over the past Gyr. This survey will complement existing imaging and will provide a rich legacy dataset for the entire community. We waive the 12 month proprietary period.
A Strong Lensing Measurement of the Evolution of Mass Structure in Giant Elliptical Galaxies
The structure and evolution of giant elliptical galaxies provide key quantitative tests for the theory of hierarchical galaxy formation in a cold dark matter dominated universe. Strong gravitational lensing provides the only direct means for the measurement of individual elliptical galaxy masses beyond the local universe, but there are currently no large and homogeneous samples of strong lens galaxies at significant cosmological look-back time. Hence, an accurate and unambiguous measurement of the evolution of the mass-density structure of elliptical galaxies has until now been impossible. Using spectroscopic data from the recently initiated Baryon Oscillation Spectroscopic Survey (BOSS) of luminous elliptical galaxies at redshifts from approximately 0.4 to 0.7, we have identified a large sample of high-probability strong gravitational lens candidates at significant cosmological look-back time, based on the detection of emission-line features from more distant galaxies along the same lines of sight as the target ellipticals. We propose to observe 45 of these systems with the ACS-WFC in order to confirm the incidence of lensing and to measure the masses of the lens galaxies. We will complement these lensing mass measurements with stellar velocity dispersions from ground-based follow-up spectroscopy. In combination with similar data from the Sloan Lens ACS (SLACS) Survey at lower redshifts, we will directly measure the cosmic evolution of the ratio between lensing mass and dynamical mass, to reveal the structural explanation for the observed size evolution of elliptical galaxies (at high mass). We will also measure the evolution of the logarithmic mass-density profile of massive ellipticals, which is sensitive to the details of the merging histories through which they are assembled. Finally, we will use our lensing mass-to-light measurements to translate the BOSS galaxy luminosity function into a mass function, and determine its evolution in combination with data from the original Sloan Digital Sky Survey.
A Snapshot Survey of The Most Massive Clusters of Galaxies
We propose the continuation of our highly successful HST/ACS SNAPshot survey of a sample of 123 very X-ray luminous clusters in the redshift range 0.3-0.7, detected and compiled by the MACS cluster survey. As demonstrated by dedicated HST observations of the 12 most distant MACS clusters (GO-09722) as well as by the MACS SNAPshots of an additional 25 obtained with ACS so far in Cycles 14 and 15, these systems frequently exhibit strong gravitational lensing as well as spectacular examples of violent galaxy evolution. A large number of additional MACS SNAPs have since been obtained with WFPC2, leading to the discovery of several more powerful cluster lenses. The dramatic loss, however, of depth, field-of-view, and angular resolution compared to ACS led to significantly reduced scientific returns, underlining the need for ACS for this project. The proposed observations will provide important constraints on the cluster mass distributions, on the physical nature of ! galaxy-galaxy and galaxy-gas interactions in cluster cores, and will yield a set of optically bright, lensed galaxies for further 8-10m spectroscopy. For those of our targets with existing ACS SNAPshot images, we propose SNAPshots in the WFC3 F110W and F140W passbands to obtain colour information that will greatly improve the secure identification of multiple-image systems and may, in the form of F606W or F814W dropouts, lead to the lensing-enabled discovery of very distant galaxies at z>5. Acknowledging the broad community interest in this sample (16 of the 25 targets of the approved MCT cluster program are MACS discoveries) we waive our data rights for these observations.
This proposal is an updated and improved version of our successful Cycle 15 proposal of the same title. Alas, SNAP-10875 collected only six snapshots in the F606W or F814W passbands, due to, first, a clerical error at STScI which caused the program to be barred from execution for four months and, ultimately, the failure of ACS. With ACS restored, and WFC3 providing additional wavelength and redshift leverage, we wish to resume this previously approved project.
COS-GTO: Io Atmosphere/STIS
We will use six HST orbits with COS to observe the disk-integrated longitudinal distribution of Io's atmosphere, and ten HST orbits with STIS to provide complementary disk-resolved information at key locations. We will use the COS G225M grating to observe four SO2 absorption bands, which can be used to determine SO2 atmospheric density. Disk-integrated 19 micron observations of the atmosphere indicate that the anti-Jupiter hemisphere of Io has an atmospheric density roughly ten times greater than the Jupiter-facing side (Spencer et al. 2005), and mm-wave observations suggest a similar pattern. However the infrared and mm-wave observations cannot easily separate atmospheric density from atmospheric temperature, so these results are model-dependent. Sparse 2100 2300 disk-resolved observations (McGrath et al. 2000, Jessup et al. 2004) tell a consistent story, but do not cover enough of Io's surface to provide full confirmation of the long-wavelength result. We will therefore observe Io's disk-integrated atmospheric density at six longitudes, roughly 30, 90, 150, 210, 270, and 330 W, to confirm the 19 micron results and improve our ability to model the 19-micron data. With STIS, we plan disk-resolved 2000-3200 spectroscopy of Io's SO2 atmosphere. Our observations will target low-latitude regions away from active plumes (in contrast to our Cycle 10 observations (Jessup et al. 2004) which targeted the Prometheus plume), to look for the effect of plumes on the atmosphere. We will also look at the variation of low-latitude atmospheric abundance with terrain type, to look for explanations for the large longitudinal variations in atmospheric pressure to be studied with COS. Finally, we will look at a variety of regions at two different times of day to determine the extent of diurnal variations in the atmosphere, which are expected if the atmosphere is dominantly supported by frost sublimation.
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.
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).
NUV Internal/External Wavelength Scale Monitor
This program monitors the offsets between the wavelength scale set by the internal wavecal versus that defined by absorption lines in external targets. This is accomplished by observing two external radial velocity standard targets: HD187691 with G225M and G285M and HD6655 with G285M and G230L. The two standard targets have little flux in the wavelength range covered by G185M and so Feige 48 (sdO) is observed with this grating. Both Feige 48 and HD6655 are also observed in SMOV. The cenwaves observed in this program are a subset of the ones used during Cycle 17. Observing all cenwaves would require a considerably larger number of orbits. Constraints on scheduling of each target are placed so that each target is observed once every ~2-3 months. Observing the three targets every month would also require a considerably larger number of orbits.
HST Cycle 17 and Post-SM4 Optical Monitor
This program is the Cycle 17 implementation of the HST Optical Monitoring Program.
The 36 orbits comprising this proposal will utilize ACS (Wide Field Channel) and WFC3 (UVIS Channel) to observe stellar cluster members in parallel with multiple exposures over an orbit. Phase retrieval performed on the PSF in each image will be used to measure primarily focus, with the ability to explore apparent coma, and astigmatism changes in WFC3.
The goals of this program are to: 1) monitor the overall OTA focal length for the purposes of maintaining focus within science tolerances 2) gain experience with the relative effectiveness of phase retrieval on WFC3/UVIS PSFs 3) determine focus offset between the imagers and identify any SI-specific focus behavior and dependencies
If need is determined, future visits will be modified to interleave WFC3/IR channel and STIS/CCD focii measurements.
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.
The Impact of Starbursts on the Gaseous Halos of Galaxies
Perhaps the most important (yet uncertain) aspects of galaxy evolution are the processes by which galaxies accrete gas and by which the resulting star formation and black hole growth affects this accreting gas. It is believed that both the form of the accretion and the nature of the feedback change as a function of the galaxy mass. At low mass the gas comes in cold and the feedback is provided by massive stars. At high mass, the gas comes in hot, and the feedback is from an AGN. The changeover occurs near the mass where the galaxy population transitions from star-forming galaxies to red and dead ones. The population of red and dead galaxies is building with cosmic time, and it is believed that feedback plays an important role in this process: shutting down star formation by heating and/or expelling the reservoir of cold halo gas. To investigate these ideas, we propose to use COS far-UV spectra of background QSOs to measure the properties of the halo gas in a sample of galaxies near the transition mass that have undergone starbursts within the past 100 Myr to 1 Gyr. The galactic wind associated with the starburst is predicted to have affected the properties of the gaseous halo. To test this, we will compare the properties of the halos of the post-starburst galaxies to those of a control sample of galaxies matched in mass and QSO impact parameter. Do the halos of the post-starburst galaxies show a higher incidence rate of Ly-Alpha and metal absorption-lines? Are the kinematics of the halo gas more disturbed in the post-starbursts? Has the wind affected the ionization state and/or the metallicity of the halo? These data will provide fresh new insights into the role of feedback from massive stars on the evolution of galaxies, and may also offer clues about the properties of the QSO metal absorption-line systems at high-redshift .
Infrared Survey of Star Formation Across Cosmic Time
We propose to use the unique power of WFC3 slitless spectroscopy to measure the evolution of cosmic star formation from the end of the reionization epoch at z>6 to the close of the galaxy-building era at z~0.3.Pure parallel observations with the grisms have proven to be efficient for identifying line emission from galaxies across a broad range of redshifts. The G102 grism on WFC3 was designed to extend this capability to search for Ly-alpha emission from the first galaxies. Using up to 250 orbits of pure parallel WFC3 spectroscopy, we will observe about 40 deep (4-5 orbit) fields with the combination of G102 and G141, and about 20 shallow (2-3 orbit) fields with G141 alone.
Our primary science goals at the highest redshifts are: (1) Detect Lya in ~100 galaxies with z>5.6 and measure the evolution of the Lya luminosity function, independent of of cosmic variance; 2) Determine the connection between emission line selected and continuum-break selected galaxies at these high redshifts, and 3) Search for the proposed signature of neutral hydrogen absorption at re-ionization. At intermediate redshifts we will (4) Detect more than 1000 galaxies in Halpha at 0.5< z<1.8 to measure the evolution of the extinction-corrected star formation density across the peak epoch of star formation. This is over an order-of-magnitude improvement in the current statistics, from the NICMOS Parallel grism survey. (5) Trace ``cosmic downsizing" from 0.5< z<2.2; and (6) Estimate the evolution in reddening and metallicty in star-forming galaxies and measure the evolution of the Seyfert population. For hundreds of spectra we will be able to measure one or even two line pair ratios -- in particular, the Balmer decrement and [OII]/[OIII] are sensitive to gas reddening and metallicity. As a bonus, the G102 grism offers the possibility of detecting Lya emission at z=7-8.8.
To identify single-line Lya emitters, we will exploit the wide 0.8--1.9um wavelength coverage of the combined G102+G141 spectra. All [OII] and [OIII] interlopers detected in G102 will be reliably separated from true LAEs by the detection of at least one strong line in the G141 spectrum, without the need for any ancillary data. We waive all proprietary rights to our data and will make high-level data products available through the ST/ECF.
Mapping the Interaction Between High-Redshift Galaxies and the Intergalactic Environment
With the commissioning of the high-throughput large-area camera WFC3/IR, it is possible for the first time to undertake an efficient survey of the rest-frame optical morphologies of galaxies at the peak epoch of star formation in the universe. We therefore propose deep WFC3/IR imaging of over 320 spectroscopically confirmed galaxies between redshift 1.6 < z < 3.4 in well-studied fields which lie along the line of sight to bright background QSOs. The spectra of these bright QSOs probe the IGM in the vicinity of each of the foreground galaxies along the line of sight, providing detailed information on the physical state of the gas at large galactocentric radii. In combination with our densely sampled UV/IR spectroscopy, stellar population models, and kinematic data in these fields, WFC3/IR imaging data will permit us to construct a comprehensive picture of the structure, dynamics, and star formation properties of a large population of galaxies in the early universe and their effect upon their cosmological environment.
Using Massive Star Clusters in Merger Remnants To Provide Reference Colors of Intermediate-Age Stellar Populations
Much current research in cosmology and galaxy formation relies on an accurate interpretation of colors of galaxies in terms of their evolutionary state, i.e., in terms of ages and metallicities. One particularly important topic is the ability to identify early-type galaxies at "intermediate" ages (~ 500 Myr - 5 Gyr), i.e., the period between the end of star formation and ~ half the age of the universe. Currently, integrated-light studies must rely on population synthesis models which rest upon spectral libraries of stars in the solar neighborhood. These models have a difficult time correctly incorporating short-lived evolutionary phases such as thermally pulsing AGB stars, which produce up to 80% of the flux in the near-IR in this age range. Furthermore, intermediate-age star clusters in the Local Group do not represent proper templates against which to calibrate population synthesis models in this age range, because their masses are too low to render the effect of stochastic fluctuations due to the number of bright RGB and AGB stars negligible. As a consequence, current population synthesis models have trouble reconciling the evolutionary state of high-redshift galaxies from optical versus near-IR colors. We propose a simple and effective solution to this issue, namely obtaining high-quality EMPIRICAL colors of massive globular clusters in galaxy merger remnants which span this important age range. These colors should serve as relevant references, both to identify intermediate-age objects in the local and distant universe and as calibrators for population synthesis modelers.
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.
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.
Obtaining the Missing Links in the Test of Very Low Mass Evolutionary Models with HST
We are proposing for spatially resolved ACS+HRC observations of 11 very low mass binaries spanning late-M, L and T spectral types in order to obtain precise effective temperature measurements for each component. All of our targets are part of a program in which we are measuring dynamical masses of very low-mass binaries to an unprecedented precision of 10% (or better). However, without precise temperature measurements, the full scientific value of these mass measurements cannot be realized. Together, mass and temperature measurements will allow us to distinguish between brown dwarf evolutionary models that make different assumptions about the interior and atmospheric structure of these ultra-cool objects. While dynamical masses can be obtained from the ground in the near-IR, obtaining precise temperatures require access to optical data which, for these sub-arcsecond binaries, can only be obtained from space with Hubble.
How Galaxies Acquire their Gas: A Map of Multiphase Accretion and Feedback in Gaseous Galaxy Halos
We propose to address two of the biggest open questions in galaxy formation - how galaxies acquire their gas and how they return it to the IGM - with a concentrated COS survey of diffuse multiphase gas in the halos of SDSS galaxies at z = 0.15 - 0.35. Our chief science goal is to establish a basic set of observational facts about the physical state, metallicity, and kinematics of halo gas, including the sky covering fraction of hot and cold material, the metallicity of infall and outflow, and correlations with galaxy stellar mass, type, and color - all as a function of impact parameter from 10 - 150 kpc. Theory suggests that the bimodality of galaxy colors, the shape of the luminosity function, and the mass-metallicity relation are all influenced at a fundamental level by accretion and feedback, yet these gas processes are poorly understood and cannot be predicted robustly from first principles. We lack even a basic observational assessment of the multiphase gaseous content of galaxy halos on 100 kpc scales, and we do not know how these processes vary with galaxy properties. This ignorance is presently one of the key impediments to understanding galaxy formation in general. We propose to use the high-resolution gratings G130M and G160M on the Cosmic Origins Spectrograph to obtain sensitive column density measurements of a comprehensive suite of multiphase ions in the spectra of 43 z < 1 QSOs lying behind 43 galaxies selected from the Sloan Digital Sky Survey. In aggregate, these sightlines will constitute a statistically sound map of the physical state and metallicity of gaseous halos, and subsets of the data with cuts on galaxy mass, color, and SFR will seek out predicted variations of gas properties with galaxy properties. Our interpretation of these data will be aided by state-of-the-art hydrodynamic simulations of accretion and feedback, in turn providing information to refine and test such models. We will also use Keck, MMT, and Magellan (as needed) to obtain optical spectra of the QSOs to measure cold gas with Mg II, and optical spectra of the galaxies to measure SFRs and to look for outflows. In addition to our other science goals, these observations will help place the Milky Way's population of multiphase, accreting High Velocity Clouds (HVCs) into a global context by identifying analogous structures around other galaxies. Our program is designed to make optimal use of the unique capabilities of COS to address our science goals and also generate a rich dataset of other absorption-line systems.
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.