NASA Hubble Space Telescope Daily Report #5111
HUBBLE SPACE TELESCOPE DAILY REPORT #5111
Continuing to Collect World Class Science
PERIOD COVERED: 5am June 4 – 5am June 7, 2010 (DOY 155/09:00z-158/09:00z)
FLIGHT OPERATIONS SUMMARY:
Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)
HSTARS:
12294 – GSAcq(2,1,1) scheduled at 156/15:48:00z and REAcq(2,1,1) scheduled at 156/17:25:05z and at 156/19:00:56z was observed to have resulted in fine lock backup (2,0,2) using FGS-2.
Observations possibly affected: COS 198 – 213, Proposal ID#11536
12295 – GSAcq(2,1,1) scheduled at 157/03:37:28z failed to fine lock backup on FGS 2.
Observations possibly affected: WFC3 147 – 149, Proposal ID#11662.
COMPLETED OPS REQUEST: (None)
COMPLETED OPS NOTES: (None)
SCHEDULED SUCCESSFUL
FGS GSAcq 26 26
FGS REAcq 21 21
OBAD with Maneuver 24 24
SIGNIFICANT EVENTS: (None)
OBSERVATIONS SCHEDULED:
WFC3/UVIS 12018
Ultra-Luminous X-Ray Sources in the Most Metal-Poor Galaxies
There is growing observational and theoretical evidence to suggest that Ultra-Luminous X-ray sources (ULX) form preferentially in low metallicity environments. Here we propose a survey of 27 nearby (< 30Mpc) star-forming Extremely Metal Poor Galaxies (Z<5% solar). There are almost no X-ray observations of such low abundance galaxies (3 in the Chandra archive). These are the most metal-deficient galaxies known, and a logical place to find ULX if they favor metal-poor systems. We plan to test recent population synthesis models which predict that ULX should be very numerous in metal-poor galaxies. We will also test the hypothesis that ULX form in massive young star clusters, and ask for HST time to obtain the necessary imaging data. ACS/WFC 12016 The Stars and Edge-on Disks of PDS 144: An Intermediate-Mass Analog of Wide T Tauri Multiple Stars High-Inclination PMS stars are optimally oriented to measure disk size, height, to detect jets, and to directly probe disk composition. Placing these data into evolutionary context requires dates for the systems and measurements of L bol, and extinction. For such stars, X-ray data provide L x, but also N(H) and the total extinction. FUV data measures L UV, and constrains the shape of the extinction curve. Recent studies have suggested that the frequency of Jovian-mass planets is higher for systems with intermediate-mass stars, due to disk mass or composition. While suitable low mass YSOs are well-represented in the Chandra and HST archives, similar data are lacking for higher mass systems. We propose joint Chandra and HST imaging of PDS 144 to fill this gap. ACS/WFC 11995 CCD Daily Monitor (Part 2) 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 320 orbits (20 weeks) from 1 February 2010 to 20 June 2010. WFC3/IR/S/C 11929 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). WFC3/IR 11926 IR Zero Points We will measure and monitor the zeropoints through the IR filters using observations of the white dwarf standard stars, GD153, GD71 and GD191B2B and the solar analog standard star, P330E. Data will be taken monthly during Cycle 17. Observations of the star cluster, NGC 104, are made twice to check color transformations. We expect an accuracy of 2% in the wide filter zeropoints relative to the HST photometric system, and 5% in the medium- and narrow-band filters. WFC3/UVIS 11912 UVIS Internal Flats This proposal will be used to assess the stability of the flat field structure for the UVIS detector throughout the 15 months of Cycle 17. The data will be used to generate on-orbit updates for the delta-flat field reference files used in the WFC3 calibration pipeline, if significant changes in the flat structure are seen. WFC3/UVIS 11908 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 3×3 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 11905 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). COS/FUV 11897 FUV Spectroscopic Sensitivity Monitoring The purpose of this proposal is to monitor sensitivity in each FUV grating mode to detect any changes due to contamination or other causes. WFC3/ACS/UVIS 11877 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. STIS/CC 11847 CCD Bias Monitor-Part 2 Monitor the bias in the 1×1, 1×2, 2×1, and 2×2 bin settings at gain=1, and 1×1 at gain = 4, to build up high-S/N superbiases and track the evolution of hot columns. STIS/CC 11845 CCD Dark Monitor Part 2 Monitor the darks for the STIS CCD. WFC3/UV 11841 The Formation of Brightest Cluster Galaxies We propose Chandra and HST observations of a unique low redshift cluster in which the Brightest Cluster Galaxy (BCG) is in the process of forming. The Chandra observations will be used to study the impact of BCG formation on the properties of the intracluster medium. We will test whether galaxy merging can destroy cool cores and disrupt hot gas halos. We will also explore the role of intracluster stars in enriching the intracluster medium. The HST observations will be used to search for extended tidal features and young star clusters and to estimate the final stellar mass of the BCG. The low redshift of our target allows a more detailed study of BCG formation than is possible with higher redshift systems. FGS 11789 An Astrometric Calibration of Population II Distance Indicators In 2002, HST produced a highly precise parallax for RR Lyrae. That measurement resulted in an absolute magnitude, M(V)= 0.61+/-0.11, a useful result, judged by the over ten refereed citations each year since. It is, however, unsatisfactory to have the direct, parallax-based, distance scale of Population II variables based on a single star. We propose, therefore, to obtain the parallaxes of four additional RR Lyrae stars and two Population II Cepheids, or W Vir stars. The Population II Cepheids lie with the RR Lyrae stars on a common K-band Period-Luminosity relation. Using these parallaxes to inform that relationship, we anticipate a zero point error of 0.04 magnitude. This result should greatly strengthen confidence in the Population II distance scale and increase our understanding of RR Lyrae star and Pop. II Cepheid astrophysics. FGS 11788 The Architecture of Exoplanetary Systems Are all planetary systems coplanar? Concordance cosmogony makes that prediction. It is, however, a prediction of extrasolar planetary system architecture as yet untested by direct observation for main sequence stars other than the Sun. To provide such a test, we propose to carry out FGS astrometric studies on four stars hosting seven companions. Our understanding of the planet formation process will grow as we match not only system architecture, but formed planet mass and true distance from the primary with host star characteristics for a wide variety of host stars and exoplanet masses. We propose that a series of FGS astrometric observations with demonstrated 1 millisecond of arc per-observation precision can establish the degree of coplanarity and component true masses for four extrasolar systems: HD 202206 (brown dwarf+planet); HD 128311 (planet+planet), HD 160691 = mu Arae (planet+planet), and HD 222404AB = gamma Cephei (planet+star). In each case the companion is identified as such by assuming that the minimum mass is the actual mass. For the last target, a known stellar binary system, the companion orbit is stable only if coplanar with the AB binary orbit. COS/NUV/FUV 11742 Probing HeII Reionization with GALEX-selected Quasar Sightlines and HST/COS We propose spectroscopic observations with COS of eight z~3 QSOs that we found to be bright in the far ultraviolet. Our aim is to study intergalactic absorption caused by the onset of the He II Lyman forest. Several lines of evidence suggest that helium reionization occurred at z~3. Understanding this process is critical for a complete picture of the intergalactic medium and its evolution; it also gives clues to hydrogen reionization at z>6. The only direct means of assessing He II reionization is through far-UV observations of the He II Lyman alpha forest. Only 6 sightlines are known to date where this is feasible, despite extensive surveys. Our program is designed to double the number of available sightlines. To this effect, we cross-correlated all known z>2.73 quasars with UV source lists from the GALEX satellite. The selected quasars were all significantly detected in the far UV by GALEX, and their UV colors are similar to those of already known quasars with transparent sightlines. Spectra obtained with COS will allow us to compile the first comprehensive sample of He II absorption spectra probing similar redshifts, enabling a systematic investigation of the He II reionization epoch and the spectral shape of the UV background.
COS/NUV/FUV 11728
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 .
FGS 11704
The Ages of Globular Clusters and the Population II Distance Scale
Globular clusters are the oldest objects in the universe whose age can be accurately determined. The dominant error in globular cluster age determinations is the uncertain Population II distance scale. We propose to use FGS 1R to obtain parallaxes with an accuracy of 0.2 milliarcsecond for 9 main sequence stars with [Fe/H] < -1.5. This will determine the absolute magnitude of these stars with accuracies of 0.04 to 0.06mag. This data will be used to determine the distance to 24 metal-poor globular clusters using main sequence fitting. These distances (with errors of 0.05 mag) will be used to determine the ages of globular clusters using the luminosity of the subgiant branch as an age indicator. This will yield absolute ages with an accuracy of 5%, about a factor of two improvement over current estimates. Coupled with existing parallaxes for more metal-rich stars, we will be able to accurately determine the age for globular clusters over a wide range of metallicities in order to study the early formation history of the Milky Way and provide an independent estimate of the age of the universe. The Hipparcos database contains only 1 star with [Fe/H] < -1.4 and an absolute magnitude error less than 0.18 mag which is suitable for use in main sequence fitting. Previous attempts at main sequence fitting to metal-poor globular clusters have had to rely on theoretical calibrations of the color of the main sequence. Our HST parallax program will remove this source of possible systematic error and yield distances to metal-poor globular clusters which are significantly more accurate than possible with the current parallax data. The HST parallax data will have errors which are 10 times smaller than the current parallax data. Using the HST parallaxes, we will obtain main sequence fitting distances to 11 globular clusters which contain over 500 RR Lyrae stars. This will allow us to calibrate the absolute magnitude of RR Lyrae stars, a commonly used Population II distance indicator. WFC3/IR 11696 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. ACS/WFC3 11670 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. WFC3/UVIS/IR 11662 Improving the Radius-Luminosity Relationship for Broad-Lined AGNs with a New Reverberation Sample The radius-luminosity (R-L) relationship is currently the fundamental basis for all techniques used to estimate black hole masses in AGNs, in both the nearby and distant universe. However, the current R-L relationship is based on 34 objects that cover a limited range in black hole mass and luminosity. To improve our understanding of black hole growth and evolution, the R-L relationship must be extended to cover a broader range of black hole masses using the technique known as reverberation mapping. To this end, we have been awarded an unprecedented 64 nights on the Lick Observatory 3-m telescope between March 24 and May 31, 2008, to spectroscopically monitor 12 AGNs in order to measure their black hole masses. To properly determine the luminosities of these 12 AGNs, we must correct them for their host-galaxy starlight contributions using high-resolution images. Previous work by Bentz et al. (2006) has shown that the starlight correction to AGN luminosity measurements is an essential component to interpreting the R-L relationship. The correction will be substantial for each of the 12 sources we will monitor, as the AGNs are relatively faint and embedded in nearby, bright galaxies. Starlight corrections are not possible with ground-based images, as the PSF and bulge contributions become indistinguishable under typical seeing conditions, and adaptive optics are not yet operational in the spectral range where the corrections are needed. In addition, spectral decompositions are very model-dependent and are limited by the degree of accuracy to which we understand emission processes and stellar populations in galaxies. Without correcting for starlight, we will be unable to apply the results of our Spring 2008 campaign to the body of knowledge from previous reverberation mapping work. Therefore, we propose to obtain high resolution, high dynamic range images of the host galaxies of the 12 AGNs in our ground-based monitoring sample, as well as one white dwarf which will be used as a PSF model. WFC3/IR 11648 WFC3 Spectroscopy of an X-ray Luminous Galaxy Cluster at z>2
We propose to obtain deep WFC3+G141 grism observations to spectroscopically confirm a remarkable z>2 cluster of galaxy candidate. Over a 1000 arcmin^2 field imaged with SpitzerOs IRAC we have discovered a compact (<30OO diameter) concentration of extremely red galaxies with a factor of >40 overdensity over the adjacent field. Among these galaxies for which we can derive meaningful photometric redshifts, 17 are consistent with zphot=2-2.5, making it very likely that the concentration is a real cluster at such high redshift. This is further supported by a 3.5 sigma detection of extended X-Ray emission on XMM-Newton data, by a likely color?magnitude sequence of red galaxies, and by the presence of a giant galaxy consistent with a BCG at the cluster redshift. The general faintness of the red galaxies in all optical bands and their high redshifts prevent confirmation of this cluster with ordinary optical spectroscopy. The WFC3 camera with G141 grism provides the only way to confirm this record high-z cluster and measure its redshift from spectral breaks typical of old stellar populations. Our deep integrations will reveal redshifts for at least 19 ultra-red galaxies in the area and of a similar number of bluer galaxies at the cluster redshift. Knowledge of the cluster redshift based on the HST spectra will allow us to reach important scientific aims: find the most distant X?ray emitting evolved galaxy cluster, determine membership of the other galaxies from photometric SED analysis, study their stellar population properties, characterize the color-magnitude relation with constraints on the formation redshift. The proposed observations will establish a first z>2 benchmark for cluster?field comparisons of galaxy formation at this highest redshift and will firmly establish the progenitors of local rich Abell clusters.
WFC3/UVIS/IR 11644
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.
WFC3/UV 11605
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.
WFC3/UVIS 11595
Turning Out the Light: A WFC3 Program to Image z>2 Damped Lyman Alpha Systems
We propose to directly image the star-forming regions of z>2 damped Lya systems (DLAs) using the WFC3/UVIS camera on the Hubble Space Telescope. In contrast to all previous attempts to detect the galaxies giving rise to high redshift DLAs, we will use a novel technique that completely removes the glare of the background quasar. Specifically, we will target quasar sightlines with multiple DLAs and use the higher redshift DLA as a “blocking filter” (via Lyman limit absorption) to eliminate all FUV emission from the quasar. This will allow us to carry out a deep search for FUV emission from the lower redshift DLA, shortward of the Lyman limit of the higher redshift absorber. The unique filter set and high spatial resolution afforded by WFC3/UVIS will then enable us to directly image the lower redshift DLA and thus estimate its size, star- formation rate and impact parameter from the QSO sightline. We propose to observe a sample of 20 sightlines, selected primarily from the SDSS database, requiring a total of 40 HST orbits. The observations will allow us to determine the first FUV luminosity function of high redshift DLA galaxies and to correlate the DLA galaxy properties with the ISM characteristics inferred from standard absorption-line analysis to significantly improve our understanding of the general DLA population.
WFC3/UV/IR 11573
Investigating Post-Equinox Atmospheric Changes on Uranus
Uranus is now past its 7 December 2007 equinox. The large seasonal phase shift expected from its long radiative time constant implies that it should now be in the process of reversing its hemispheric asymmetries in cloud band structure and zonal circulation. Many changes already observed — the development of the first visible-wavelength dark spot, discovered in Cycle 15, the fading of the south polar cap, and the development of a new northern bright band while the southern band fades — may all be indicative of the expected reversal. We propose a detailed characterization of Uranus’ current seasonal response with a 9-orbit program consisting of 3 orbits of WFC3 imaging of cloud bands and dark spots, and 6 orbits of high signal-to-noise imaging using the F845M filter, capable of tracking bright discrete cloud features. Filters between 0.467 and 1.7 microns will provide vertical sensing depths scanning through the pressure range where the putative methane and deeper H2S clouds might plausibly exist and provide strong constraints on their contributions and parent gas mixing ratios. These observations have unique combinations of spectral range and resolution with needed temporal sampling and spatial resolution not available from groundbased observations.
WFC3/ACS/UVIS/IR 11570
Narrowing in on the Hubble Constant and Dark Energy
A measurement of the Hubble constant to a precision of a few percent would be a powerful aid to the investigation of the nature of dark energy and a potent “end-to end” test of the present cosmological model. In Cycle 15 we constructed a new streamlined distance ladder utilizing high- quality type Ia supernova data and observations of Cepheids with HST in the near-IR to minimize the dominant sources of systematic uncertainty in past measurements of the Hubble constant and reduce its total uncertainty to a little under 5%. Here we propose to exploit this new route to reduce the remaining uncertainty by more than 30%, translating into an equal reduction in the uncertainty of the equation of state of dark energy. We propose three sets of observations to reach this goal: a mosaic of NGC 4258 with WFC3 in F160W to triple its sample of long period Cepheids, WFC3/F160W observations of the 6 ideal SN Ia hosts to triple their samples of Cepheids, and observations of NGC 5584 the host of a new SN Ia, SN 2007af, to discover and measure its Cepheids and begin expanding the small set of SN Ia luminosity calibrations. These observations would provide the bulk of a coordinated program aimed at making the measurement of the Hubble constant one of the leading constraints on dark energy.
WFC3/UV/COS/FUV 11536
COS-GTO: Sleuthing the Source of Distant Cometary Activity
Distant comets and Centaurs often show cometary activity and outbursts well beyond 3 AU, the boundary of the sublimation zone of water. Super-volatiles (most likely CO, but possibly CH4, N2, or S2) are suspected to be responsible, but have never been detected in distant comets in the UV. We will obtain FUV spectra of active bodies to cover important CO emission bands. We plan two sets of observations: comet 29P/Schwassmann-Wachmann at 6 AU, whose outbursts are too short to capture as a Target of Opportunity, but which also shows persistent cometary activity in quiescence; and Target of Opportunity observations of the Centaur 2060 Chiron (at ~15.5 AU) in outburst.
ACS/WFC 11338
Continued M31 Monitoring for Black Hole X-ray Nova
During A01-7 we found >16 Black Hole X-ray Novae (BHXN) in M31 using Chandra, and with HST followup have estimated orbital periods for 6 of these. Observations are underway with HST to attempt to estimate additional periods. We propose to continue this program, concentrating our scarce HST resources on a single transient which exceeds the NS Eddington limit. Only uninterrupted monitoring can yield the duty cycles and long-term lightcurves of BHXN (and other variables) in M31. Our GO+GTO programs have accumulated 300ks (ACIS) near the M31 bulge, and total ACIS exposure on M31 is now 620ks. Our monitoring program alone can amass 500ks on the bulge if continued through AO12, and combined with other programs will reach >1Msec ACIS exposure on the bulge.
