NASA Hubble Space Telescope Daily Report #5067
HUBBLE SPACE TELESCOPE DAILY REPORT #5067
Continuing to Collect World Class Science
PERIOD COVERED: 5am April 2 – 5am April 5, 2010 (DOY 092/09:00z-095/09:00z)
OBSERVATIONS SCHEDULED
WFC3/IR/S/C 12097
Additional IR Subarray Dark Current Measurements (in support of GO programs 11205, 11580)
This proposal will produce IR dark images necessary to calibrate GO science observations (already taken, see proposals 11205 and 11580) that use observing modes not supported by the existing IR dark current monitor (proposal 11929). These modes are as follows: SQ256SUB/SPARS100, SQ256SUB/SPARS200, SQ512SUB/SPARS10, SQ512SUB/SPARS100, and SQ512SUB/SPARS200.
WFC3/IR 12088
Tungsten lamp warm-up time
The purpose of this proposal is to determine the time required for the primary UVIS & IR tungsten lamps to fully warm up and output to stabilize.
WFC3/UV 12077
Monitoring the Aftermath of an Asteroid Impact Event
Our Director’s Discretionary program (GO-12053) to image the newly discovered object P/2010 A2 executed successfully on 2010 Jan 25 and 29 with spectacular results. Hubble has apparently borne witness to the first detection of a collision in the asteroid belt. Hubble imaging with the WFC3 has revealed an object unlike anything ever seen before and with details impossible to detect with any other facility. We request 6 more orbits of Hubble time (1 orbit every 20 days over the next few months, until the object enters Hubble’s solar exclusion zone in late-June 2010) to monitor the evolution of this remarkable object and further clarify the nature of this event. These observations may usher in a new era of searching for and characterizing collisional events within the asteroid belt.
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/UV 11918
WFC3 UVIS Image Quality
The UVIS imaging performance over the detector will be assessed periodically (every 4 months) in two passbands (F275W and F621M) to check for image stability. The field around star 58 in the open cluster NGC188 is the chosen target because it is sufficiently dense to provide good sampling over the FOV while providing enough isolated stars to permit accurate PSF (point spread function) measurement. It is available year-round and used previously for ACS image quality assessment. The field is astrometric, and astrometric guide stars will be used, so that the plate scale and image orientation may also be determined if necessary (as in SMOV proposals 11436 and 11442). Full frame images will be obtained at each of 4 POSTARG offset positions designed to improve sampling over the detector.
This proposal is a periodic repeat (once every 4 months) of visits similar to those in SMOV proposal 11436 (activity ID WFC3-23). The data will be analyzed using the code and techniques described in ISR WFC3 2008-40 (Hartig). Profiles of encircled energy will be monitored and presented in an ISR. If an update to the SIAF is needed, (V2, V3) locations of stars will be obtained from the Flight Ops Sensors and Calibrations group at GSFC, the (V2, V3) of the reference pixel and the orientation of the detector will be determined by the WFC3 group, and the Telescopes group will update and deliver the SIAF to the PRDB branch.
The specific PSF metrics to be examined are encircled energy for aperture diameter 0.15, 0.20, 0.25, and 0.35 arcsec, FWHM, and sharpness. (See ISR WFC3 2008-40 tables 2 and 3 and preceding text.) about 20 stars distributed over the detector will be measured in each exposure for each filter. The mean, rms, and rms of the mean will be determined for each metric. The values determined from each of the 4 exposures per filter within a visit will be compared to each other to see to what extent they are affected by “breathing”. Values will be compared from visit to visit, starting with the values obtained during SMOV after the fine alignment has been performed, to see if the measures of the compactness of the PSF indicate degradation over time. The analysis will be repeated for stars on the inner part of the detector and stars on the outer part of the detector to check for differential degradation of the PSF.
As an example of the analysis, one can examine the sharpness of the F275W PSF exposures made during thermal vacuum testing (ISR WFC3 2008-40). To compare two samples, one can define the PSFs on each CCD chip as a sample of 8. The mean, rms, and rms of the mean sharpness are 0.0676, 0.0093, and 0.0035 for one chip, and 0.0701, 0.0085, and 0.0032 for the other. The difference of the means is 0.0025 and the statistical error in that difference is 0.0048, so the difference is not significant.
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 11907
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 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).
WFC3/UVIS 11903
UVIS Photometric Zero Points
This proposal obtains the photometric zero points in 53 of the 62 UVIS/WFC3 filters: the 18 broad-band filters, 8 medium-band filters, 16 narrow-band filters, and 11 of the 20 quad filters (those being used in cycle 17). The observations will be primary obtained by observing the hot DA white dwarf standards GD153 and G191-B2B. A redder secondary standard, P330E, will be observed in a subset of the filters to provide color corrections. Repeat observations in 16 of the most widely used cycle 17 filters will be obtained once per month for the first three months, and then once every second month for the duration of cycle 17, alternating and depending on target availability. These observations will enable monitoring of the stability of the photometric system. Photometric transformation equations will be calculated by comparing the photometry of stars in two globular clusters, 47 Tuc and NGC 2419, to previous measurements with other telescopes/instruments.
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.
ACS/WFC/WFC3/IR 11802
WFC3/IR Observations of Strongly Lensing Clusters
We propose WFC3/IR observations of the massive lensing clusters Abell 1689 and Abell 1703 to constrain the properties of both cluster and background field galaxies. The dataset will also help constrain the photometric redshift of A1689-zD1, the bright galaxy candidate at z~7.6.
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.
STIS/CC/MA 11736
The Nearest Cold Interstellar Cloud
Optical observations of interstellar Na I absorption have recently discovered that a cold (20 K) diffuse cloud stretching over 10 degrees across the constellation Leo is nearby (d < 45 pc) and thus, deep inside the Local Bubble of hot, tenuous gas surrounding the Sun out to distances of ~100 pc. Assuming thermal pressure equilibrium under these conditions leads to an extremely thin, sheetlike geometry for the cold Leo cloud. Such a cold cloud could also be the overpressured interface between colliding flows of warm gas in the Local Bubble. The keys to evaluating the gas pressure and other physical characteristics of the cold Leo cloud lie in the ultraviolet with its rich diversity of interstellar diagnostic transitions. Due in part to a lack of bright UV background sources, there has been no previous UV absorption line study of this cloud. We have identified 3 stars exhibiting Na I absorption from the cold Leo cloud that are suitable for such a study with STIS onboard HST. The main goals of our proposed observations are to: (1) determine the cloud's gas pressure through measurements of its C I fine-structure excitation, (2) assess the dust contribution to the cloud heating by measuring the depletion-sensitive Cr/Zn gas-phase abundance ratio, and (3) evaluate the cloud cooling rate and electron density through measurements of its C II fine-structure excitation. WFC3/UVIS 11732 The Temperature Profiles of Quasar Accretion Disks We can now routinely measure the size of quasar accretion disks using gravitational microlensing of lensed quasars. At optical wavelengths we observe a size and scaling with black hole mass roughly consistent with thin disk theory but the sizes are larger than expected from the observed optical fluxes. One solution would be to use a flatter temperature profile, which we can study by measuring the wavelength dependence of the disk size over the largest possible wavelength baseline. Thus, to understand the size discrepancy and to probe closer to the inner edge of the disk we need to extend our measurements to UV wavelengths, and this can only be done with HST. For example, in the UV we should see significant changes in the optical/UV size ratio with black hole mass. We propose monitoring 5 lenses spanning a broad range of black hole masses with well-sampled ground based light curves, optical disk size measurements and known GALEX UV fluxes during Cycles 17 and 18 to expand from our current sample of two lenses. We would obtain 5 observations of each target in each Cycle, similar to our successful strategy for the first two targets. 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. COS/FUV 11687 SNAPing Coronal Iron This is a Snapshot Survey to explore two forbidden lines of highly ionized iron in late-type coronal sources. Fe XII 1349 (T~ 2 MK) and Fe XXI 1354 (T~ 10 MK) — well known to Solar Physics — have been detected in about a dozen cool stars, mainly with HST/STIS. The UV coronal forbidden lines are important because they can be observed with velocity resolution of better than 15 km/s, whereas even the state-of-the-art X-ray spectrometers on Chandra can manage only 300 km/s in the kilovolt band where lines of highly ionized iron more commonly are found. The kinematic properties of hot coronal plasmas, which are of great interest to theorists and modelers, thus only are accessible in the UV at present. The bad news is that the UV coronal forbidden lines are faint, and were captured only in very deep observations with STIS. The good news is that 3rd-generation Cosmic Origins Spectrograph, slated for installation in HST by SM4, in a mere 25 minute exposure with its G130M mode can duplicate the sensitivity of a landmark 25-orbit STIS E140M observation of AD Leo, easily the deepest such exposure of a late-type star so far. Our goal is to build up understanding of the properties of Fe XII and Fe XXI in additional objects beyond the current limited sample: how the lineshapes depend on activity, whether large scale velocity shifts can be detected, and whether the dynamical content of the lines can be inverted to map the spatial morphology of the stellar corona (as in “Doppler Imaging”). In other words, we want to bring to bear in the coronal venue all the powerful tricks of spectroscopic remote sensing, well in advance of the time that this will be possible exploiting the corona’s native X-ray radiation. The 1290-1430 band captured by side A of G130M also contains a wide range of key plasma diagnostics that form at temperatures from below 10, 000 K (neutral lines of CNO), to above 200, 000 K (semi-permitted O V 1371), including the important bright multiplets of C II at 1335 and Si IV at 1400; yielding a diagnostic gold mine for the subcoronal atmosphere. Because of the broad value of the SNAP spectra, beyond the coronal iron project, we waive the normal proprietary rights. WFC3/IR 11666 Chilly Pairs: A Search for the Latest-type Brown Dwarf Binaries and the Prototype Y Dwarf We propose to use HST/NICMOS to image a sample of 27 of the nearest (< 20 pc) and lowest luminosity T-type brown dwarfs in order to identify and characterize new very low mass binary systems. Only 3 late-type T dwarf binaries have been found to date, despite that fact that these systems are critical benchmarks for evolutionary and atmospheric models at the lowest masses. They are also the most likely systems to harbor Y dwarf companions, an as yet unpopulated putative class of very cold (T < 600 K) brown dwarfs. Our proposed program will more than double the number of T5-T9 dwarfs imaged at high resolution, with an anticipated yield of ~5 new binaries with initial characterization of component spectral types. We will be able to probe separations sufficient to identify systems suitable for astrometric orbit and dynamical mass measurements. We also expect one of our discoveries to contain the first Y-type brown dwarf. Our proposed program complements and augments ongoing ground-based adaptive optics surveys and provides pathway science for JWST. WFC3/IR/ACS/WFC 11663 Formation and Evolution of Massive Galaxies in the Richest Environments at 1.5 < z < 2.0 We propose to image seven 1.5< z<2 clusters and groups from the IRAC Shallow Cluster Survey with WFC3 and ACS in order to study the formation and evolution of massive galaxies in the richest environments in the Universe in this important redshift range. We will measure the evolution of the sizes and morphologies of massive cluster galaxies, as a function of redshift, richness, radius and local density. In combination with allocated Keck spectroscopy, we will directly measure the dry merger fraction in these clusters, as well as the evolution of Brightest Cluster Galaxies (BCGs) over this redshift range where clear model predictions can be confronted. Finally we will measure both the epoch of formation of the stellar populations and the assembly history of that stellar mass, the two key parameters in the modern galaxy formation paradigm. WFC3/UVIS 11650 Mutual Orbits, Colors, Masses, and Bulk Densities of 3 Cold Classical Trans-Neptunian Binaries Many Trans-Neptunian Objects (TNOs) have been found to be binary or multiple systems. As in other astrophysical settings, Trans-Neptunian Binaries (TNBs) offer uniquely valuable information. Their mutual orbits allow the direct determination of their system masses, perhaps the most fundamental physical quantity of any astronomical object. Their frequency of occurrence and dynamical characteristics provide clues to formation conditions and evolution scenarios affecting both the binaries and their single neighbors. Combining masses with sizes, bulk densities can be measured. Densities constrain bulk composition and internal structure, key clues to TNO origins and evolution over time. Several TNB bulk densities have been determined, hinting at interesting trends. But none of them belongs to the Cold Classical sub-population, the one group of TNOs with demonstrably distinct physical characteristics. Two top-priority Spitzer programs will soon observe and measure the sizes of 3 Cold Classical TNBs. This proposal seeks to determine the mutual orbits and thus masses of these systems, enabling computation of their densities. 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/UVIS 11643 A Timeline for Early-Type Galaxy Formation: Mapping the Evolution of Star Formation, Globular Clusters, Dust, and Black Holes While considerable effort has been devoted to statistical studies of the origin of the red sequence of galaxies, there has been relatively little direct exploration of galaxies transforming from late to early types. Such galaxies are identified by their post-starburst spectra, bulge- dominated, tidally-disturbed morphologies, and current lack of gas. We are constructing the first detailed timeline of their evolution onto the red sequence, pinpointing when star formation ends, nuclear activity ceases, globular clusters form, and the bulk of the merging progenitors’ dust disappears. Here we propose to obtain HST and Chandra imaging of nine galaxies, whose wide range of post-starburst ages we have precisely dated with a new UV-optical technique and for which we were awarded Spitzer time. We will address 1) whether the black hole-bulge mass relation arises from nuclear feedback, 2) whether the bimodality of globular cluster colors is due to young clusters produced in galaxy mergers, and 3) what happens to the dust when late types merge to form an early type. WFC3/UV 11635 Improve the Measurement of Vesta’s Pole Orientation to Support Dawn Mission NASA?s Dawn spacecraft is scheduled to go into orbit around the main belt asteroid 4 Vesta in July 2011. Currently the project is using a 3-? pole position uncertainty of Vesta of 12? for spacecraft trajectory design. We have determined that with an additional set of Hubble observations at Vesta?s next opposition in February 2010, that the pole position uncertainty can be reduced by a factor of 4. This will reduce both cost and risk to the Dawn mission, and is likely to increase the stay time at Vesta and will add to the scientific return of the mission. The requested observing window in February 2010 is the last and single best opportunity that can benefit the Dawn mission, but it is before the start of the next HST Cycle. WFC3/UV/IR 11620 A Quasar Light Echo in the Local Universe? The time history and duty cycle of individual AGN is an important part of their evolution and the growth history of massive black holes, but almost unconstrained on scales between galaxy-interaction timescales (hundreds of Myr) and the scales of years probed by variability measurements. We propose a detailed study of an object which seems to be a large-scale light echo from a QSO-level episode in a nearby galaxy. The Galaxy Zoo morphological survey of SDSS objects has uncovered a peculiar emission-line structure whose spectrum matches the narrow-line region of AGN, despite lying at least 20 kpc from a galaxy whose activity is currently very weak. This is best explained if the nucleus has faded dramatically on time scales of several tens of thousands of years. We propose a suite of imaging and spectroscopic observations to probe its properties, and the time history of this episode of nuclear activity, measuring time scales hitherto unavailable. COS/NUV/FUV 11598 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 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. COS/NUV 11561 An Intensive COS Spectroscopic Study of the Planetary Debris Disks Around two Warm White Dwarfs It is very likely that the gas giants in our Solar system will survive the evolution of the Sun into a white dwarf, and the same is thought to be generally true for Jovian planets around solar-like stars if their initial orbits are wider than ~3AU. Despite this prediction, no unambiguous detection of a planet around a white dwarf has been announced so far. However, over the past few years, about a dozen white dwarfs have been identified which host metal-rich debris disks that are thought to stem from the tidal disruption of asteroids. In most cases the debris disks are observed in the form of an infrared flux excess, and offer relatively little diagnostic potential for the study of their structure. We have discovered three warm (T~20000K) white dwarfs with metal-rich debris disks in a gaseous phase which display strong double-peaked CaII emission lines in the I-band and weak Fe 5169A emission. The line profiles can be modeled in terms of Keplerian disks with an extension of ~1Rsun around the white dwarfs. Photospheric MgII 4481A absorption demonstrates that the white dwarfs are accreting from the debris disks. Besides these spectral features, the optical wavelength range is devoid of other useful metal transitions. Here, we propose an intensive spectroscopic ultraviolet study of these systems, which will provide (a) ~1000 photospheric absorption lines of 15 chemical elements, allowing an accurate abundance study of the material accreted from the debris disks, and (b) ~2 dozen additional emission lines of Mg, Cr, Ti, and Fe that will provide detailed insight into the dynamical, thermal, and density structure of these exo-planetary debris disks. FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTARS: 12236 – GSAcq(1,2,1) at 093/21:14:08z failed to RGA control with Search Radius Limit exceeded on FGS 1. Observations affected: COS 137 – 141, proposal ID#11687. COMPLETED OPS REQUEST: (None) COMPLETED OPS NOTES: (None)
SCHEDULED SUCCESSFUL
FGS GSAcq 22 21
FGS REAcq 25 25
OBAD with Maneuver 18 18
SIGNIFICANT EVENTS: (None)
