NASA Hubble Space Telescope Daily Report #4028

Status Report From: Space Telescope Science Institute
Posted: Monday, January 16, 2006


HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science


PERIOD COVERED: UT January 13,14,15, 2006 (DOY 013,014,015)


WFPC2 10778

WFPC2 WF4 Supplemental Darks

A anomaly has been found in images from the WF4 CCD in WFPC2. The WF4 CCD bias level appears to have become unstable, resulting in sporadic images with either low or zero bias level. The severity and frequency of the problem is rapidly increasing, and it is possible that WF4 will soon become unusable if no work-around is found. The other three CCDs {PC1, WF2, and WF3} appear to be unaffected and continue to operate properly. These darks are to supplement those in program 10748 to ensure sufficient dark frames for routine calibration. As the WF4 anomaly grows worse, we are beginning to see episodes where too many darks are corrupted and are unusable.

WFPC2 10744

WFPC2 Cycle 14 Decontaminations and Associated Observations

This proposal is for the WFPC2 decons. Also included are instrument monitors tied to decons: photometric stability check, focus monitor, pre- and post-decon internals {bias, intflats, kspots, & darks}, UV throughput check, VISFLAT sweep, and internal UV flat check.

ACS/HRC 10738

Earth Flats

Sky flats will be obtained by observing the bright Earth with the HRC and WFC. These observations will be used to verify the accuracy of the flats currently in the pipeline and to monitor any changes. Weekly coronagraphic monitoring is required to assess the changing position of the spots.


ACS CCDs daily monitor

This program consists of a set of basic tests to monitor, the read noise, the development of hot pixels and test for any source of noise in ACS CCD detectors. The files, biases and dark will be used to create reference files for science calibration. This programme will be for the entire lifetime of ACS. Changes from cycle 13:- The default gain for WFC is 2 e-/DN. As before bias frames will be collected for both gain 1 and gain 2. Dark frames are acquired using the default gain {2}. This program cover the period Oct, 2 2005- May, 29-2006. The second half of the program has a different proposal number: 10758.

ACS/WFC 10629

Are Field OB Stars Alone?

This SNAP program offers an inexpensive, simple program to search for low-mass companions of field OB stars. Do field OB stars exist in true isolation, as suggested by a recent Galactic study, or are they the tip of the iceberg on a small cluster of low-mass stars as predicted by the cluster mass function and stellar IMF? Short ACS/WFC V and I observations proposed here may easily resolve this issue for field OB stars in the Small Magellanic Cloud. Truly isolated OB stars represent a theoretical challenge and variation from clusters, in mode of star formation, and have important consequences for our understanding of the field stellar population in galaxies. Small clusters around the field OB stars, on the other hand, may confirm the universality of the stellar clustering law and IMF.

ACS/WFC 10626

A Snapshot Survey of Brightest Cluster Galaxies and Strong Lensing to z = 0.9

We propose an ACS/WFC snapshot survey of the cores of 150 rich galaxy clusters at 0.3 < z < 0.9 from the Red Sequence Cluster Survey {RCS}. An examination of the galaxian light in the brightest cluster galaxies, coupled with a statistical analysis of the strong-lensing properties of the sample, will allow us to contrain the evolution of both the baryonic and dark mass in cluster cores, over an unprecedented redshift range and sample size. In detail, we will use the high- resolution ACS images to measure the metric {10 kpc/h} luminosity and morphological disturbances around the brightest clusters galaxies, in order to calibrate their accretion history in comparison to recent detailed simulations of structure formation in cluster cores. These images will also yield a well-defined sample of arcs formed by strong lensing by these clusters; the frequency and detailed distribution {size, multiplicity, redshifts} of these strong lens systems sets strong constraints on the total mass content {and its structure} in the centers of the clusters. These data will also be invaluable in the study of the morphological evolution and properties of cluster galaxies over a significant redshift range. These analyses will be supported by extensive ongoing optical and near-infrared imaging, and optical spectroscopy at Magellan, VLT and Gemini telescopes, as well as host of smaller facilities.

WFPC2 10619

Dynamical Masses and Third Bodies in the Sirius System

Sirius B is the nearest and brightest of all white dwarfs {WDs}, but it is fiendishly difficult to observe from the ground because of the overwhelming brightness of Sirius A. We propose a continuation of our program of imaging observations of the Sirius system with WFPC2, which has been underway since 2001. The resulting astrometric data will not only greatly improve the precision of the binary orbit and the dynamical mass measurements for both the main-sequence and WD components, but will also test definitively for the claimed presence of a third body in this famous system, down to planetary masses. At present, there is a tantalizing suggestion in our data that there indeed may exist a substellar or planetary third body in the system. Our team has also obtained superb spectra of Sirius B using STIS, and we have achieved an excellent fit to the spectrum using model stellar atmospheres. However, the implied mass of the WD disagrees significantly with the dynamical mass implied by the existing visual-binary orbit {which still has to be based on a combination of low-accuracy ground-based astrometry plus the small number of existing HST astrometric observations}. This is another critical motivation for improving the astrometry.

ACS/WFC 10595

A Reference Database for Accurate Ages and Metallicities of Globular Clusters in the Magellanic Clouds

We propose to finalize the compilation of a comprehensive database of high-quality ages and metallicities of Simple Stellar Populations {SSPs} in the Milky Way and the Magellanic Clouds. We will acquire new ACS imagery for 8 young and intermediate-age globular clusters in the Magellanic Clouds to create high-quality color-magnitude diagrams {CMDs} to enable accurate measurements of their ages and metallicities. In concert with a similar analysis of CMD data already available in the HST archive for 8 more such GCs, the resulting database will provide a well-sampled coverage of the full range of ages and metallicities known among globular clusters {0.5 <= Age {Gyr} <= 13.5 and -2.3 <= [Fe/H] <= +0.1, respectively}. This database will form the crucial basis for our ongoing, comprehensive multi-wavelength program to: {1} establish empirical relations among SSP colors {from the UV [GALEX] through the mid-IR [Spitzer]}, line strengths, ages and metallicities, and {2} provide a stringent test of the systemic accuracy of age and metallicity determinations using state-of-the-art population synthesis models.


The Formation of Spiral Spheroids and Their Globular Cluster Systems

The assembly history of spiral galaxies remains one of the most pressing questions in astrophysics today. In particular, we do not have a clear picture of the formation mechanism for bulges of spiral galaxies. Are bulges of spirals simply "small ellipticals", formed via rapid dissipative collapse during the early universe? Or is bulge building through secular evolution of inner disk stars a more common mechanism? Is there any dependence on bulge mass? A powerful yet relatively simple way to probe these fundamental questions is by studying the properties of globular cluster {GC} systems of spirals. Specifically, bulge formation via secular evolution is expected not to form GCs, whereas bulge formation via dissipative collapse is. We therefore propose to obtain ACS/WFC imaging as well as ground-based, wide-field imaging of five edge-on Sa spirals which cover a factor ~15 in luminosity/mass, and for which spectroscopic follow-up is feasible. This constitutes the first luminosity-selected sample of early-type spirals, which will allow us to directly probe the dependence of GC properties on the bulge luminosity. We will detect a minimum of ~100-200 GCs per galaxy in the ACS images, sufficient to reveal GC subpopulations, their relative numbers, sizes, and radial distributions. This study will more than double the number of well-studied early-type spiral systems.

ACS/WFC 10591

ACS Observations of the Galaxies in A Giant Ly-alpha Nebula at z~2.7

Giant Ly-alpha nebulae appear to be sites of ongoing massive galaxy formation, as evidenced by their association with very luminous, young, star-forming galaxies and large galaxy overdensities. However the origin of the extended gas and the source of ionization remain mysterious. We have discovered a ~200 kpc size nebula which appears to contain a number of embedded sources, including a very obscured, luminous mid-infrared source and a Lyman break galaxy. We propose to obtain deep ACS and NICMOS images of this nebula in order to: {i} determine the spatial morphology of the Ly-alpha emission on sub-kpc scales; {ii} precisely locate the known continuum sources within the nebula; {ii} determine their morphologies; {iii} detect the source of ionizing photons at the very center of the nebula; {iv} constrain the ionizing luminosity contributed by a possible distributed population of faint, compact continuum sources in the nebula; and {v} by SED fitting of population synthesis models, constrain the ages of the ionizing sources with the aim of determining the timescale of the galaxy formation process in the nebula.

ACS/WFC 10587

Measuring the Mass Dependence of Early-Type Galaxy Structure

We propose two-color ACS-WFC Snapshot observations of a sample of 118 candidate early- type gravitational lens galaxies. Our lens-candidate sample is selected to yield {in combination with earlier results} an approximately uniform final distribution of 40 early-type strong lenses across a wide range of masses, with velocity dispersions {a dynamical proxy for mass} ranging from 125 to 300 km/s. The proposed program will deliver the first significant sample of low-mass gravitational lenses. All of our candidates have known lens and source redshifts from Sloan Digital Sky Survey data, and all are bright enough to permit detailed photometric and stellar- dynamical observation. We will constrain the luminous and dark-matter mass profiles of confirmed lenses using lensed-image geometry and lens-galaxy structural/photometric measurements from HST imaging in combination with dynamical measurements from spatially resolved ground-based follow-up spectroscopy. Hence we will determine, in unprecedented detail, the dependence of early-type galaxy mass structure and mass-to-light ratio upon galaxy mass. These results will allow us to directly test theoretical predictions for halo concentration and star-formation efficiency as a function of mass and for the existence of a cuspy inner dark- matter component, and will illuminate the structural explanation behind the fundamental plane of early-type galaxies. The lens-candidate selection and confirmation strategy that we propose has been proven successful for high-mass galaxies by our Cycle 13 Snapshot program {10174}. The program that we propose here will produce a complementary and unprecedented lens sample spanning a wide range of lens-galaxy masses.

ACS/HRC 10556

Neutral Gas at Redshift z=0.5

Damped Lyman-alpha systems {DLAs} are used to track the bulk of the neutral hydrogen gas in the Universe. Prior to HST UV spectroscopy, they could only be studied from the ground at redshifts z>1.65. However, HST has now permitted us to discover 41 DLAs at z<1.65 in our previous surveys. Followup studies of these systems are providing a wealth of information about the evolution of the neutral gas phase component of the Universe. But one problem is that these 41 low-redshift systems are spread over a wide range of redshifts spanning nearly 70% of the age of the Universe. Consequently, past surveys for low-redshift DLAs have not been able to offer very good precision in any small redshift regime. Here we propose an ACS-HRC- PR200L spectroscopic survey in the redshift interval z=[0.37, 0.7] which we estimate will permit us to discover another 41 DLAs. This will not only allow us to double the number of low-redshift DLAs, but it will also provide a relatively high-precision regime in the low-redshift Universe that can be used to anchor evolutionary studies. Fortunately DLAs have high absorption equivalent width, so ACS-HRC-PR200L has high-enough resoultion to perform this proposed MgII-selected DLA survey.

ACS/SBC 10554

Globular Cluster Systems of Elliptical Galaxies in Low Density Environments

We propose to use the ACS/WFC to determine colour {metallicity} distributions and luminosity functions for the globular cluster populations in a well-defined sample of elliptical galaxies in low- density environments, and to compare the results with similar samples taken from a rich cluster environment. Low-luminosity ellipticals are now recognized to play a pivotal role in testing hierarchical models of galaxy formation, and their globular cluster populations provide a unique probe of their star formation and metal enrichment history. The data will be used to {i} determine whether the bimodal colour distributions indicative of multiple formation epochs in luminous ellipticals are also prevalent in low-luminosity field ellipticals; {ii} place joint constraints on age and metallicity in systems with more than one population and determine the spread of ages in any one system; {iii} test whether cluster destruction processes {e.g. tidal shocking} are more effective in low-luminosity ellipticals, as predicted from their higher mass densities. ACS observations are essential to eliminate foreground/background contamination and to probe deep into the luminosity function to obtain a good statistical sample of clusters. The TAC has previously awarded HST time to two large surveys of globular cluster systems in rich cluster environments, but there is currently no comparable survey in low-density environments with which to compare these results.

ACS/WFC 10543

Microlensing in M87 and the Virgo Cluster

Resolving the nature of dark matter is an urgent problem. The results of the MACHO survey of the Milky Way dark halo toward the LMC indicate that a significant fraction of the halo consists of stellar mass objects. The VATT/Columbia survey of M31 finds a similar lens fraction in the M31 dark halo. We propose a series of observations with ACS that will provide the most thorough search for microlensing toward M87, the central elliptical galaxy of the Virgo cluster. This program is optimized for lenses in the mass range from 0.01 to 1.0 solar masses. By comparing with archival data, we can detect lenses as massive as 100 solar masses, such as the remnants of the first stars. These observations will have at least 15 times more sensitivity to microlensing than any previous survey, e.g. using WFPC2. This is due to the factor of 2 larger area, factor of more than 4 more sensitivity in the I-band, superior pixel scale and longer baseline of observations. Based on the halo microlensing results in the Milky Way and M31, we might expect that galaxy collisions and stripping would populate the overall cluster halo with a large number of stellar mass objects. This program would determine definitively if such objects compose the cluster dark matter at the level seen in the Milky Way. A negative result would indicate that such objects do not populate the intracluster medium, and may indicate that galaxy harassment is not as vigorous as expected. We can measure the level of events due to the M87 halo: this would be the best exploration to date of such a lens population in an elliptical galaxy. Star-star lensing should also be detectable. About 20 erupting classical novae will be seen, allowing to determine the definitive nova rate for this giant elliptical galaxy. We will determine if our recent HST detection of an M87 globular cluster nova was a fluke, or indicative of a 100x higher rate of incidence of cataclysmic variables and nova eruptions in globulars than previously believed. We will examine the populations of variable stars, and will be able to cleanly separate them from microlensing.

ACS/WFC 10491

A Snapshot Survey of the most massive clusters of galaxies

We propose a snapshot survey of a sample of 124 high X-ray luminosity clusters in the redshift range 0.3-0.7. Similarly luminous clusters at these redshifts frequently exhibit strong gravitational lensing. The proposed observations will provide important constraints on the nature of the cluster mass distributions and a set of optically bright, lensed galaxies for further 8-10m spectroscopy. We acknowledge the broad community interest in this sample and waive our data rights for these observations.

ACS/WFC 10490

A Snapshot Survey of a Complete Sample of X-ray Luminous Galaxy Clusters from Redshift 0.3 to 0.7

We propose to extend a public, uniform imaging survey of a well-studied, complete, and homogeneous sample of X-ray clusters. The sample of 72 clusters spans the redshift range between 0.3-0.7 and almost 2 orders of magnitude of X-ray luminosity, with a median luminosity of 10^44 erg/s {0.5-2.0 keV}. These snapshots will be used to obtain a fair census of the morphologies of cluster galaxies in the cores of intermediate redshift clusters, to detect radial and tangential arc candidates, to detect optical jet candidates, and to provide an approximate estimate of the shear signal of the clusters themselves and a potential assessment of the contribution of large scale structure to lensing shear.

ACS/HRC 10476

Accurate Mass Determination of the Ancient White Dwarf ER 8 Through Astrometric Microlensing

We propose to determine the mass of the very cool white dwarf ER 8 through astrometric microlensing. We have predicted that ER 8 will pass very close to a 15th-mag background star in January 2006, with an impact parameter of less than 0.05 arcsec. As it passes in front, it will cause a deflection of the background star's image by >8 milliarcsec, an amount easily detectable with HST/FGS. The gravitational deflection angle depends only on the distances and relative positions of the stars, and on the mass of the white dwarf. Since the distances and positions can be determined precisely before the event, the astrometric measurement offers a unique and direct method to measure the mass of the white dwarf to high accuracy {<5%}. Unlike all other stellar mass determinations, this technique works for single stars {but only if they are nearby and of sufficient mass}. The mass of ER 8 is of special interest because it is a member of the Galactic halo, and appears to be the oldest known field white dwarf. This object can thus set a lower limit on the age of the Galactic halo, but since white-dwarf cooling rates depend on their masses, the mass is a necessary ingredient in the age determination. As a byproduct, we will obtain an accurate parallax for ER 8, and thus its luminosity and {from its effective temperature} its radius. Such quantities are at present rather poorly known for the coolest white dwarfs, and will provide strong constraints on white-dwarf physics.

ACS/HRC 10396

Star Clusters, Stellar Populations, and the Evolution of the Small Magellanic Cloud

As the closest star forming dwarf galaxy, the SMC is the preferred location for detailed studies of this extremely common class of objects. We therefore propose to use the capabilities of ACS, which provide an improvement by an order of magnitude over what is possible with ground- based optical imaging surveys that are limited by confusion anddepth, to measure key stellar population parameters in the SMC from VI color-magnitude diagrams. Our program focuses on regions where crowding makes HST essential and includes 7 star clusters and 7 field star locations. We will measure accurate ages of the clusters, test stellar evolution models, gain fiducial stellar sequences to use in fitting the field stars, check the form of the IMF, and substantially extend the study of RR Lyrae variables in the key NGC121 SMC globular cluster. The field pointings will allow us to reconstruct the star formation history, look for enhanced star formation that is expected when the SMC interacts with the LMC and/or Milky Way, and compare its main sequence luminosity {and mass} functions with those of the Milky Way, LMC, and UMi dwarf spheroidal. This proposal is part of a coordinated HST and ground-based study of the stellar history and star formation processes in the SMC.


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


10085 - Trickle Charge Elapsed Timer (QTCELAP) @ 016/04:43:35z

The Trickle Charge Elapsed Timer (QTCELAP) exceeded the ground limit of 6900 sec reaching 6982 sec. OPS Note 1435-1, Limits for QTCELAP "Trickle Charge Elapsed Timer", reset the ground limit from 6000 sec to 6900 sec to accommodate variations in trickle charge while in taper charge control. Trickle charge reached at 04:44:52GMT, approx. 17 minutes prior to entering orbit night.

10083 - REacq(2,1,2) failed to RGA control (T2G) ,ESB message observed at AOS @ 015/21:13:20z

The REacq(2,1,2) scheduled during ZOE at 015/21:13:20 - 21:21:25 failed to RGA control (T2G) at AOS 015/21:36:45 (TWD).One 486 ESB message A0E(hex) was also observed at AOS when telemetry was reacquired, indicating FGS Sequential Attitude Update failed because roll error was too large to correct (QDVEFGS1=221.458 arcsecs). OBAD attitude correction was not scheduled prior to acquisition. Real-time OBAD impossible due to ZOE. Subsequent OBAD at 015/21:21:24 had total (RSS) attitude correction of 6.65 arcsecs. Ref HSTAR 10082 has the same star id. OBAD corrction scheduled prior to the next GSacq at 015/22:43:43.

10082 - GSacq(2,1,2) results in finelock backup (1,0,1) due to scan step limit exceeded on FGS-2 @ 15/19:40:34z

At AOS 015/20:00:55, the GSacq(2,1,2) scheduled at 015/19:40:34 - 19:48:39 resulted to finelock backup (1,0,1) using FGS-1,due to scan step limit exceeded indication flags on FGS-2. Prior OBAD at 015/19:36:04 had total (RSS) attitude correction of 4.47 arcsecs.Subsequent OBAD/Map at 015/19:48:38 had total (RSS) attitude correction of 6.79 arcsecs.


17626-0 - Table 320 dump @ 013/1654z

17627-0 - Modify SOC Benchmark & ACR 2 High Limit @ 013/1731z

17628-0 - Full RAM Memory Dump @ 014/0049z


                        SCHEDULED      SUCCESSFUL      FAILURE TIMES
FGS GSacq               23                     23
REacq               19                     18                015/21:13:20z 
(HSTAR #10083)
OBAD with Maneuver  79                     79


Flash Report: Taper Charge status, Sunday 1/15/06 11:59pm - (16 Jan 2006 01:03:29) -- As of DOY 015 00:00 - 016 02:00:00 (Sunday 1/15): -- General Performance Notes -- 1) System Full SOC (pressure based) varied from 243 to 249Ah. (since DOY 015 00:00:00) 2) The minimum margin to SOC1 (181Ah) at the end of orbit night was 14.2Ah. 3) The difference between FSW SOC and PSI based SOC was +/-6Ah. (since DOY 015 00:00:00) 4) Battery Temperatures: Bat 1 Min -2.6, Max 0.4, Mean -0.9; Bat 2 Min -1.5, Max 0.6, Mean -0.6; Bat 3 Min -1.7, Max 0.7, Mean -0.7; Bat 4 Min -1.5, Max 0.7, Mean -0.5; Bat 5 Min -1.1, Max 1.0, Mean 0.1; Bat 6 Min -1.4, Max 0.6, Mean -0.6 -- The system continues to perform well with stable SOC, as well as, converged and reduced battery temperatures.

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