Status Report

NASA Hubble Space Telescope Daily Report #5089

By SpaceRef Editor
May 6, 2010
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Continuing to Collect World Class Science

PERIOD COVERED: 5am May 4 – 5am May 5, 2010 (DOY 124/09:00z-125/09:00z)


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.

ACS/WFC/WFC3/UVI 11636 First Resolved Imaging of Escaping Lyman Continuum

The emission from star-forming galaxies appears to be responsible for reionization of the universe at z > 6. However, the models that attempt to describe the detailed impact of high-redshift galaxies on the surrounding inter-galactic medium (IGM) are strongly dependent upon several uncertain parameters. Perhaps the most uncertain is the fraction of HI-ionizing photons produced by young stars that escape into the IGM. Most attempts to measure this “escape fraction” have produced null results. Recently, a small subset of z~3 Lyman Break Galaxies (LBGs) has been found exhibiting large escape fractions. It remains unclear however, what differentiates them from other LBGs. Several models attempt to explain how such a large fraction of ionizing continuum can escape through the HI and dust in the ISM (eg. “chimneys” created by SNe winds, globular cluster formation, etc.), each producing unique signatures which can be observed with resolved imaging of the escaping Lyman continuum. To date, there are only six LBGs with individual detections of escaping Lyman continuum at any redshift. We propose a single deep, high resolution WFC3/UVIS image of the ionizing continuum (F336W) and the rest-frame UV/optical (F606W/F814W/F160W) of five of these six LBGs with large escape fractions. These LBGs have a high surface density and large escape fractions, and lie at the optimal redshift for Lyman continuum imaging with UVIS filters, making our sample especially suitable for follow-up. With these data we will discern the mechanisms responsible for producing large escape fractions, and therefore gain insight into the process of reionization.

ACS/WFC/WFC3/UVI 1739 Multiple Stellar Generations in the Unique Globular Clusters NGC 6388 and NGC 6441

Over the last few years HST observations have resulted in one of the most exciting and unexpected developments in stellar population studies: the discovery of multiple generations of stars in several globular clusters. The finding of multiple main sequences in the massive clusters NGC 2808 and Omega Centauri, and multiple subgiant branches in NGC 1851, M54, and NGC 6388 has challenged the long-held paradigm that globular clusters are simple stellar populations. Even more surprising, given the spectroscopic and photometric constraints, the only viable explanation for the main sequence splitting appears to be Helium enrichment, up to an astonishingly high Y=0.4. The conditions under which certain globulars experience the formation of multiple stellar generations remain mysterious, and even more so the helium-enrichment phenomenon. Such an enrichment has important implications for chemical-enrichment, star-formation, and stellar-evolution scenarios, in star clusters and likely elsewhere. To properly constrain the multiple main sequence phenomenon, it is important to determine its extent among GCs: is it limited to Omega Cen and NGC2808, or is it more common? We propose deep WFC3 optical/IR imaging of NGC 6388 and 6441, the two globular clusters that are most likely to host multiple, helium-enriched populations. Our simulations of WFC3 performance suggest that we will be able to detect even the main sequence splittings caused by small He differences (Delta Y <0.03). ACS/WFC/WFC3/UVI 12020 The Deepest Stellar X-ray/optical Census of the Bulge We have obtained the deepest optical dataset ever taken or planned towards the bulge, allowing bulge/disk decomposition down to F606W=23 and variability monitoring over seven days, diagnostics not available for any bulge field observed by Chandra. We propose ACIS-I imaging to identify X-ray point sources in this field. This will directly trace a number of fundamental yet poorly-constrained parameters of the inner Milky Way, for example the spin-down timescale of stars along the disk and bulge; the formation history of the bulge and, for the first time, direct constraints on the gravitational potential of the inner milky way through AGN-enabled absolute proper motions. Our proposed survey will be an essential calibrator for other X-ray/optical surveys of the bulge both past and planned. COS/FUV/COS/NUV 11645 HST COS Observations of the Atmosphere and Airglow/Aurora of Enceladus Recent observations from several instruments on the Cassini spacecraft have revealed plumes of dust and water from the southern polar region, and clearly shown that Enceladus contributes large amounts of plasma to Saturn?s magnetosphere. This implies a global thin atmosphere containing water and likely other species, and a local region with orders of magnitude higher density near the plumes. While water and dust have been identified from the plumes, the presence of many other species in the atmosphere is possible and not yet ruled out. The identification of all significant species in the atmosphere of Enceladus is of key importance to speculation about the source of the water plumes, and the implications for any form of life at or below the surface. In addition, modeling suggests that Enceladus? mass loading region may be comparable in extent to Io?s, and interacts strongly with Saturn?s corotating magnetic field and plasma. We have recently concluded a search for an auroral footprint of Enceladus in HST images, which set a low upper limit implying that the magnetospheric interaction is concentrated near Enceladus, rather than being communicated along field lines to Saturn?s ionosphere. The next step will be to observe the interaction at the satellite, and to learn whatever we can about the physics of the release of the atmospheric gas. We propose here an exploratory set of spectral observations with HST COS to measure the solar reflection spectrum over a broad range of UV wavelengths for atmospheric absorption signatures. This will at the same time measure the emission spectrum of the atmosphere from both the leading and trailing hemispheres ? Enceladus orbit apart, as was done in HST STIS observations of Io to study its interaction at Jupiter. The higher sensitivity of COS will be needed to study the much smaller and relatively weakly-interacting Enceladus, and the outcome of these observations will determine the nature of future studies of the atmosphere of Enceladus and its plasma interaction with the Saturnian magnetosphere. COS/NUV/S/C 11891 NUV MAMA Fold Distribution The performance of MAMA microchannel plate can be monitored using a MAMA fold analysis procedure. The fold analysis provides a measurement of the distribution of charge cloud sizes incident upon the anode giving some measure of changes in the pulse-height distribution of the MCP and, therefore, MCP gain. This proposal executes the same steps as the COS SMOV as proposal 13555 (visit 5). STIS/CCD 11845 CCD Dark Monitor Part 2 Monitor the darks for the STIS CCD. STIS/CCD 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/CCD/STIS/MA2 11568 A SNAPSHOT Survey of the Local Interstellar Medium: New NUV Observations of Stars with Archived FUV Observations We propose to obtain high-resolution STIS E230H SNAP observations of MgII and FeII interstellar absorption lines toward stars within 100 parsecs that already have moderate or high-resolution far-UV (FUV), 900-1700 A, observations available in the MAST Archive. Fundamental properties, such as temperature, turbulence, ionization, abundances, and depletions of gas in the local interstellar medium (LISM) can be measured by coupling such observations. Due to the wide spectral range of STIS, observations to study nearby stars also contain important data about the LISM embedded within their spectra. However, unlocking this information from the intrinsically broad and often saturated FUV absorption lines of low-mass ions, (DI, CII, NI, OI), requires first understanding the kinematic structure of the gas along the line of sight. This can be achieved with high resolution spectra of high-mass ions, (FeII, MgII), which have narrow absorption lines, and can resolve each individual velocity component (interstellar cloud). By obtaining short (~10 minute) E230H observations of FeII and MgII, for stars that already have moderate or high-resolution FUV spectra, we can increase the sample of LISM measurements, and thereby expand our knowledge of the physical properties of the gas in our galactic neighborhood. STIS is the only instrument capable of obtaining the required high resolution data now or in the foreseeable future. STIS/MA1 11861 MAMA FUV Flats This program will obtain FUV-MAMA observations of the STIS internal Krypton lamp to construct an FUV flat applicable to all FUV modes. STIS/MA2 11857 STIS Cycle 17 MAMA Dark Monitor This proposal monitors the behavior of the dark current in each of the MAMA detectors. The basic monitor takes two 1380s ACCUM darks each week with each detector. However, starting Oct 5, pairs are only included for weeks that the LRP has external MAMA observations planned. The weekly pairs of exposures for each detector are linked so that they are taken at opposite ends of the same SAA free interval. This pairing of exposures will make it easier to separate long and short term temporal variability from temperature dependent changes. For both detectors, additional blocks of exposures are taken once every six months. These are groups of five 1314 s FUV-MAMA TIME-TAG darks or five 3×315 s NUV ACCUM darks distributed over a single SAA free interval. This will give more information on the brightness of the FUV MAMA dark current as a function of the amount of time that the HV has been on, and for the NUV MAMA will give a better measure of the short term temperature dependence. WFC3/IR/WFC3/UVI 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 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/UVI 11628 Globular Cluster Candidates for Hosting a Central Black Hole We are continuing our study of the dynamical properties of globular clusters and we propose to obtain surface brightness profiles for high concentration clusters. Our results to date show that the distribution of central surface brightness slopes do not conform to standard models. This has important implications for how they form and evolve, and suggest the possible presence of central intermediate-mass black holes. From our previous archival proposals (AR-9542 and AR-10315), we find that many high concentration globular clusters do not have flat cores or steep central cusps, instead they show weak cusps. Numerical simulations suggest that clusters with weak cusps may harbor intermediate-mass black holes and we have one confirmation of this connection with omega Centauri. This cluster shows a shallow cusp in its surface brightness profile, while kinematical measurements suggest the presence of a black hole in its center. Our goal is to extend these studies to a sample containing 85% of the Galactic globular clusters with concentrations higher than 1.7 and look for objects departing from isothermal behavior. The ACS globular cluster survey (GO-10775) provides enough objects to have an excellent coverage of a wide range of galactic clusters, but it contains only a couple of the ones with high concentration. The proposed sample consists of clusters whose light profile can only be adequately measured from space-based imaging. This would take us close to completeness for the high concentration cases and therefore provide a more complete list of candidates for containing a central black hole. The dataset will also be combined with our existing kinematic measurements and enhanced with future kinematic studies to perform detailed dynamical modeling. WFC3/UVI 11630 Monitoring Active Atmospheres on Uranus and Neptune We propose Snapshot observations of Uranus and Neptune to monitor changes in their atmospheres on time scales of weeks and months, as we have been doing for the past seven years. Previous Hubble Space Telescope observations (including previous Snapshot programs 8634, 10170, 10534, and 11156), together with near-IR images obtained using adaptive optics on the Keck Telescope, reveal both planets to be dynamic worlds which change on time scales ranging from hours to (terrestrial) years. Uranus equinox occurred in December 2007, and the northern hemisphere is becoming fully visible for the first time since the early 1960s. HST observations during the past several years (Hammel et al. 2005, Icarus 175, 284 and references therein) have revealed strongly wavelength-dependent latitudinal structure, the presence of numerous visible-wavelength cloud features in the northern hemisphere, at least one very long-lived discrete cloud in the southern hemisphere, and in 2006 the first clearly defined dark spot seen on Uranus. Long-term ground-based observations (Lockwood and Jerzekiewicz, 2006, Icarus 180, 442; Hammel and Lockwood 2007, Icarus 186, 291) reveal seasonal brightness changes that seem to demand the appearance of a bright northern polar cap within the next few years. Recent HST and Keck observations of Neptune (Sromovsky et al. 2003, Icarus 163, 256 and references therein) show a general increase in activity at south temperate latitudes until 2004, when Neptune returned to a rather Voyager-like appearance with discrete bright spots rather than active latitude bands. Further Snapshot observations of these two dynamic planets will elucidate the nature of long-term changes in their zonal atmospheric bands and clarify the processes of formation, evolution, and dissipation of discrete albedo features. WFC3/UVI 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 (11909), will be used to generate the necessary superbias and superdark reference files for the calibration pipeline (CDBS). WFC3/UVI 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. FLIGHT OPERATIONS SUMMARY: Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.) HSTARS: 12269 – STIS Status Buffer Messages #645, #646 and #556 received 124/22:54:24z-124/22:55:29z COMPLETED OPS REQUEST: (None) COMPLETED OPS NOTES: (None)

FGS GSAcq 10 10
FGS REAcq 6 6
OBAD with Maneuver 7 7


Flash Report

At 124/22:54z, during a STIS MAMA1 monitor HV ramp, two consecutive event yellow limits were exceeded. After the second consecutive out of limit, the HV was turned off and event flag 2 was set.

SpaceRef staff editor.