Status Report

NASA Hubble Space Telescope Daily Report #5110

By SpaceRef Editor
June 10, 2010
Filed under , ,


Continuing to Collect World Class Science

PERIOD COVERED: 5am June 3 – 5am June 4, 2010 (DOY 154/09:00z-155/09:00z)


Significant Spacecraft Anomalies: (The following are preliminary reports of potential non-nominal performance that will be investigated.)

HSTARS: (None)



FGS GSAcq 9 9
FGS REAcq 10 10
OBAD with Maneuver 8 8



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.

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. S/C 12046 COS FUV DCE Memory Dump Whenever the FUV detector high voltage is on, count rate and current draw information is collected, monitored, and saved to DCE memory. Every 10 msec the detector samples the currents from the HV power supplies (HVIA, HVIB) and the AUX power supply (AUXI). The last 1000 samples are saved in memory, along with a histogram of the number of occurrences of each current value. In the case of a HV transient (known as a “crackle” on FUSE), where one of these currents exceeds a preset threshold for a persistence time, the HV will shut down, and the DCE memory will be dumped and examined as part of the recovery procedure. However, if the current exceeds the threshold for less than the persistence time (a “mini-crackle” in FUSE parlance), there is no way to know without dumping DCE memory. By dumping and examining the histograms regularly, we will be able to monitor any changes in the rate of “mini-crackles” and thus learn something about the state of the detector. STIS/CC 11845 CCD Dark Monitor Part 2 Monitor the darks for the STIS CCD. 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. WFC3/ACS/UVIS 11613 GHOSTS: Stellar Outskirts of Massive Spiral Galaxies We propose to continue our highly successful GHOSTS HST survey of the resolved stellar populations of nearby, massive disk galaxies using SNAPs. These observations provide star counts and color-magnitude diagrams 2-3 magnitudes below the tip of the Red Giant Branch of the outer disk and halo of each galaxy. We will measure the metallicity distribution functions and stellar density profiles from star counts down to very low average surface brightnesses, equivalent to ~32 V-mag per square arcsec. This proposal will substantially improve our unique sampling of galaxy outskirts. Our targets cover a range in galaxy mass, luminosity, inclination, and morphology. As a function of these galaxy properties, this survey provides: – the most extensive, systematic measurement of radial light profiles and axial ratios of the diffuse stellar halos and outer disks of spiral galaxies; – a comprehensive analysis of halo metallicity distributions as function of galaxy type and position within the galaxy; – an unprecedented study of the stellar metallicity and age distribution in the outer disk regions where the disk truncations occur; – the first comparative study of globular clusters and their field stellar populations. We will use these fossil records of the galaxy assembly process to test halo formation models within the hierarchical galaxy formation scheme. 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/IR 11631 Binary Brown Dwarfs and the L/T Transition Brown dwarfs traverse spectral types M, L and T as their atmospheric structure evolves and they cool into oblivion. This SNAPSHOT program will obtain WFC3-IR images of 45 nearby late-L and early-T dwarfs to investigate the nature of the L/T transition. Recent analyses have suggested that a substantial proportion of late-L and early-T dwarfs are binaries, comprised of an L dwarf primary and T dwarf secondary. WFC3-IR observations will let us quantify this suggestion by expanding coverage to a much larger sample, and permitting comparison of the L/T binary fraction against ?normal? ultracool dwarfs. Only eight L/T binaries are currently known, including several that are poorly resolved: we anticipate at least doubling the number of resolved systems. The photometric characteristics of additional resolved systems will be crucial to constraining theoretical models of these late-type ultracool dwarfs. Finally, our data will also be eminently suited to searching for extremely low luminosity companions, potentially even reaching the Y dwarf regime. WFC3/IR 11712 Calibration of Surface Brightness Fluctuations for WFC3/IR We aim to characterize galaxy surface brightness fluctuations (SBF), and calibrate the SBF distance method, in the F110W and F160W filters of the Wide Field Camera 3 IR channel. Because of the very high throughput of F110W and the good match of F160W to the standard H band, we anticipate that both of these filters will be popular choices for galaxy observations with WFC3/IR. The SBF signal is typically an order of magnitude brighter in the near-IR than in the optical, and the characteristics (sensitivity, FOV, cosmetics) of the WFC3/IR channel will be enormously more efficient for SBF measurements than previously available near-IR cameras. As a result, our proposed SBF calibration will allow accurate distance derivation whenever an early-type or bulge-dominated galaxy is observed out to a distance of 150 Mpc or more (i.e., out to the Hubble flow) in the calibrated passbands. For individual galaxy observations, an accurate distance is useful for establishing absolute luminosities, black hole masses, linear sizes, etc. Eventually, once a large number of galaxies have been observed across the sky with WFC3/IR, this SBF calibration will enable accurate mapping of the total mass density distribution in the local universe using the data available in the HST archive. The proposed observations will have additional important scientific value; in particular, we highlight their usefulness for understanding the nature of multimodal globular cluster color distributions in giant elliptical galaxies. 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/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/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/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 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 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.

SpaceRef staff editor.