Status Report

NASA Hubble Space Telescope Daily Report #5105

By SpaceRef Editor
May 29, 2010
Filed under , ,


Continuing to Collect World Class Science

PERIOD COVERED: 5am May 26 – 5am May 27, 2010 (DOY 146/09:00z-147/09:00z)


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

HSTARS: (None)



FGS GSAcq 07 07
FGS REAcq 08 08
OBAD with Maneuver 04 04



COS/FUV 11592

Testing the Origin(s) of the Highly Ionized High-Velocity Clouds: A Survey of Galactic Halo Stars at z>3 kpc

Cosmological simulation predicts that highly ionized gas plays an important role in the formation and evolution of galaxies and their interplay with the intergalactic medium. The NASA HST and FUSE missions have revealed high-velocity CIV and OVI absorption along extragalactic sightlines through the Galactic halo. These highly ionized high-velocity clouds (HVCs) could cover 85% of the sky and have a detection rate higher than the HI HVCs. Two competing, equally exciting, theories may explain the origin of these highly ionized HVCs: 1) the “Galactic” theory, where the HVCs are the result of feedback processes and trace the disk-halo mass exchange, perhaps including the accretion of matter condensing from an extended corona; 2) the “Local Group” theory, where they are part of the local warm-hot intergalactic medium, representing some of the missing baryonic matter of the Universe. Only direct distance determinations can discriminate between these models. Our group has found that some of these highly ionized HVCs have a Galactic origin, based on STIS observations of one star at z<5.3 kpc. We propose an HST FUV spectral survey to search for and characterize the high velocity NV, CIV, and SiIV interstellar absorption toward 24 stars at much larger distances than any previous searches (4< d<21 kpc, 3<|z|<13 kpc). COS will provide atomic to highly ionized species (e.g., OI, CII, CIV, SiIV) that can be observed at sufficient resolution (R~22, 000) to not only detect these highly ionized HVCs but also to model their properties and understand their physics and origins. This survey is only possible because of the high sensitivity of COS in the FUV spectral range. COS/FUV 11692 The LMC as a QSO Absorption Line System We propose to obtain high resolution, high signal-to-noise observations of QSOs behind the Large Magellanic Clouds. These QSOs are situated beyond the star forming disk of the galaxy, giving us the opportunity to study the distribution of metals and energy in regions lacking significant star formation. In particular, we will derive the metallicities and study the ionization characteristics of LMC gas at impact parameters 3-17 kpc. We will compare our results with high-z QSO absorption line systems. COS/FUV 11895 FUV Detector Dark Monitor Monitor the FUV detector dark rate by taking long science exposures without illuminating the detector. The detector dark rate and spatial distribution of counts will be compared to pre-launch and SMOV data in order to verify the nominal operation of the detector. Variations of count rate as a function of orbital position will be analyzed to find dependence of dark rate on proximity to the SAA. Dependence of dark rate as function of time will also be tracked. COS/FUV/COS/NUV 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 along a significant total pathlength through the IGM (Delta z ~ 20). COS/FUV/COS/NUV 11829 Coronal and Transition Region Heating Due to Magnetic Activity on Metal-Poor Dwarf Stars How does low metallicity affect the heating and resultant temperature structure of the chromospheres, transition regions, and coronae of old solar-like dwarf stars? Our ACIS-S observations of 7 Gyr old Arcturus Moving Group (AMG) dwarfs show very little conventional coronal (> 1 MK) plasma and suggest that these stars have insufficient magnetic energy input to power a solar-like corona. However, they do have chomospheres and transition regions similar to the minimum activity Quiet Sun. It this typical or an aberration of the AMG? We propose a 35 ksec ACIS-S observation and HST COS spectroscopy of the nearest (9.2 pc), truely metal-poor ([Fe/H] = -1.4) dwarf star that is known to have definite magnetic dynamo activity (activity cycles, active region modulation) — HD103095 — to investigate this question further.

COS/NUV 11667

Detailed Probing of a 3000 km/s Ly-alpha + Metal Line Absorption Complex Near Two Galaxies at z=0.67

At intermediate redshifts, Ly-alpha absorbers cluster around rich metal-line systems [those with numerous low and high ionization species (Bahcall et al.)], and at z=3, higher ionization clouds reside at the velocity extremes of clustered Ly-alpha lines, a signature of the physics of collapse and layered gas structures (Songaila & Cowie). These extraordinary HI environments provide unique astrophysical laboratories for probing relatively high overdensity IGM structures and for placing powerful constraints on our understanding of the intergalactic medium and extended galaxy halos in the context of structure evolution, galactic stellar feedback chemical enrichment to large galactocentric distances, and the cosmic baryon budget.

We have undertaken a comprehensive study of the remarkable 1400 km/s velocity width, optically thin Ly-alpha only complex (five components) at z=0.67 within 1600 km/s of the Lyman limit z=0.66 metal-line system toward TON 153 (Churchill et al.). We have collected FOS, STIS, and HIRES quasar spectra covering the Lyman series, OVI, CIV, and MgII absorption, an F702W/WFPC-2 image, and set of ground based narrow-band SDSS filter images of the quasar field. Two galaxies aligned in velocity with the z=0.67 Ly-alpha complex and z=0.66 metal-line system lie within 100 kpc of the quasar sightline; the absorption is not consistent with our standard model of extended “halo” gas for either galaxy, which suggests that a large scale structure (i.e., filament) may extend between these galaxies.

We propose to obtain G160M/1600 and G185M/1921+1941 (S/N>10) COS spectra of the z=1.01 quasar TON 153 to obtain detailed kinematic, chemical, and ionization conditions of this extraordinary absorber/galaxy system (total velocity spread 3000 km/s). The propose observations will provide an unprecedented first high resolution examination of the full Lyman series and MgII, CIV, and OVI metal lines arising in galaxy halos or a possible large scale structure (i.e., filament) asscociated with thoroughly studied galaxies. We aim to discern if the HI extends between the galaxies and test for multiphase absorption signatures suggestive of a galactic feedback or large scale collapsing structure.

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 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/CCD 11567 Boron Abundances in Rapidly Rotating Early-B Stars. Models of rotation in early-B stars predict that rotationally driven mixing should deplete surface boron abundances during the main-sequence lifetime of many stars. However, recent work has shown that many boron depleted stars are intrinsically slow rotators for which models predict no depletion should have occurred, while observations of nitrogen in some more rapidly rotating stars show less mixing than the models predict. Boron can provide unique information on the earliest stages of mixing in B stars, but previous surveys have been biased towards narrow-lined stars because of the difficulty in measuring boron abundances in rapidly rotating stars. The two targets observed as part of our Cycle 13 SNAP program 10175, just before STIS failed, demonstrate that it is possible to make useful boron abundance measurements for early-B stars with Vsin(i) above 100 km/s. We propose to extend that survey to a large enough sample of stars to allow statistically significant tests of models of rotational mixing in early-B stars. 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. WFC3/UVI 11909 UVIS Hot Pixel Anneal The on-orbit radiation environment of WFC3 will continually generate new hot pixels. This proposal performs the procedure required for repairing those hot pixels in the UVIS CCDs. During an anneal, the two-stage thermo-electric cooler (TEC) is turned off and the four-stage TEC is used as a heater to bring the UVIS CCDs up to ~20C. As a result of the CCD warmup, a majority of the hot pixels will be fixed; previous instruments such as WFPC2 and ACS have seen repair rates of about 80%. Internal UVIS exposures are taken before and after each anneal, to allow an assessment of the procedure’s effectiveness in WFC3, provide a check of bias, global dark current, and hot pixel levels, as well as support hysteresis (bowtie) monitoring and CDBS reference file generation. One IR dark is taken after each anneal, to provide a check of the IR detector.

SpaceRef staff editor.