Status Report

NASA Hubble Space Telescope Daily Report #4254

By SpaceRef Editor
December 8, 2006
Filed under , ,
NASA Hubble Space Telescope Daily Report #4254


– Continuing to collect World Class Science

PERIOD COVERED: UT December 06, 2006 (DOY 340)


ACS/HRC 10867

SAINTS – Supernova 1987A INTensive Survey

SAINTS is a program to observe SN 1987A, the brightest supernova in 383 years, as it morphs into the youngest supernova remnant at age 19. HST is a unique tool for spatially-resolved observations of the many physical components of SN 1987A. A violent encounter is now underway between the fastest-moving debris and the circumstellar ring: the collision excites “hotspots” that light up suddenly. The optical, infrared and X-ray fluxes are rising rapidly and vary significantly on 6-month time scales: regularly-spaced HST, SPITZER, and CHANDRA observations are needed to understand the physics of these shocked regions. In Cycle 15, the many separate hotspots may begin to fuse as the shock fully enters the circumstellar ring. Photons from these shocks may excite previously invisible gas outside the ring, revealing the true extent of the mass loss that preceded the explosion of Sanduleak -69 202. The inner debris of the explosion itself, still excited by radioactive isotopes produced in the explosion, is now resolved by ACS and seen to be aspherical, providing direct evidence on the asymmetry of the explosion. Many questions about SN 1987A remain unanswered despite our diligent efforts at observation and analysis since the launch of HST. How did the enigmatic three rings form? Precisely what took place in the core during the core collapse and bounce? Is a black hole or a neutron star left behind in the debris? The rich and deep data set from SAINTS will be a resource for current use and for future reference to help answer these central questions of supernova science.

ACS/HRC 10878

An ACS Prism Snapshot Survey for z~2 Lyman Limit Systems

We propose to conduct a spectroscopic survey of Lyman limit absorbers at redshifts 1.7 < z < 2.2, using ACS/HRC and the PR200L prism. We have selected 100 quasars at 2.3 < z < 2.6 from the Sloan Digital Sky Survey Spectroscopic Quasar sample, for which no BAL signature is found at the QSO redshift and no strong metal absorption lines are present at z > 2.3 along the lines of sight. The survey has three main observational goals. First, we will determine the redshift frequency dN/dz of the LLS over the column density range 16.3 < log N_HI < 20.3 cm^-2. Second, we will measure the column density frequency distribution f{N} for the partial Lyman limit systems {PLLS} over the column density range 16.3 < log N_HI < 17.5 cm^-2. Third, we will identify new sightlines for measurements of the primordial D/H ratio. With this survey, we will also constrain two key quantities of cosmological relevance: First, the measurements of dN/dz for optically thick LLS and f{N} for the PLLS are critical to estimating the attenuation of extragalactic ionizing sources {e.g. QSOs}. Currently, uncertainties in dN/dz and f{N} are the greatest sources of uncertainty for inferring the shape and intensity of the UV background radiation field. Second, we will estimate the amount of metals in the LLS using the f{N} and ground based observations of metal line transitions. It is possible that a significant fraction of the "missing metals" at z~2 are associated with these highly ionized absorbers. Third, analysis of the LLS lends to investigations of the interface between galaxies {i.e. the damped Lyman alpha systems} and the intergalactic medium {i.e. the Lyman alpha forest}. This survey is ideal for a snapshot observing program, because the on-object integration times are less than 10 minutes, and the targets cover the majority of the northern sky.

ACS/HRC 11041

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. For cycle 15 the program will cover 18 months 12.1.06->05.31.08 and it has been divied into three different proposal each covering six months. The three proposals are 11041-11042-11043.

ACS/SBC 10840

The FUV fluxes of Tauri stars in the Taurus molecular cloud

Present and forthcoming ground-based and space surveys of the T Tauri stars in the Taurus molecular cloud will provide information from high energy stellar and accretion radiation to low energy solid state and molecular emission from the disk, making those stars perfect laboratories to carry out self-consistent studies of disk physics and evolution. We propose to complete this wealth of information by obtaining ACS/FUV spectra for a significant sample of Taurus T Tauri stars, covering a range of accretion properties and dust evolutionary stages. FUV fluxes carry ~ 10 – 100 more energy than X-rays into these disks and are thus crucial gas heating agents and key to disk dispersal by photoevaporation. These observations are a pre-requisite to interpret observations with Spitzer, SOFIA, Herschel, and ALMA, and will become one of the important legacies of HST to the star formation community.

ACS/WFC 10815

The Blue Hook Populations of Massive Globular Clusters

Blue hook stars are a class of hot {~35,000 K} subluminous horizontal branch stars that have been recently discovered using HST ultraviolet images of the globular clusters omega Cen and NGC 2808. These stars occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. Using new theoretical evolutionary and atmospheric models, we have shown that the blue hook stars are very likely the progeny of stars that undergo extensive internal mixing during a late helium core flash on the white dwarf cooling curve. This “flash mixing” produces an enormous enhancement of the surface helium and carbon abundances, which suppresses the flux in the far ultraviolet. Although flash mixing is more likely to occur in stars that are born with high helium abundances, a high helium abundance, by itself, does not explain the presence of a blue hook population – flash mixing of the envelope is required. We propose ACS ultraviolet {SBC/F150LP and HRC/F250W} observations of the five additional globular clusters for which the presence of blue hook stars is suspected from longer wavelength observations. Like omega Cen and NGC 2808, these five targets are also among the most massive globular clusters, because less massive clusters show no evidence for blue hook stars. Because our targets span 1.5 dex in metallicity, we will be able to test our prediction that flash-mixing should be less drastic in metal-rich blue hook stars. In addition, our observations will test the hypothesis that blue hook stars only form in globular clusters massive enough to retain the helium-enriched ejecta from the first stellar generation. If this hypothesis is correct, then our observations will yield important constraints on the chemical evolution and early formation history in globular clusters, as well as the role of helium self-enrichment in producing blue horizontal branch morphologies and multiple main sequence turnoffs. Finally, our observations will provide new insight into the formation of the hottest horizontal branch stars, with implications for the origin of the hot helium-rich subdwarfs in the Galactic field.

ACS/WFC 10886

The Sloan Lens ACS Survey: Towards 100 New Strong Lenses

As a continuation of the highly successful Sloan Lens ACS {SLACS} Survey for new strong gravitational lenses, we propose one orbit of ACS-WFC F814W imaging for each of 50 high- probability strong galaxy-galaxy lens candidates. These observations will confirm new lens systems and permit immediate and accurate photometry, shape measurement, and mass modeling of the lens galaxies. The lenses delivered by the SLACS Survey all show extended source structure, furnishing more constraints on the projected lens potential than lensed-quasar image positions. In addition, SLACS lenses have lens galaxies that are much brighter than their lensed sources, facilitating detailed photometric and dynamical observation of the former. When confirmed lenses from this proposal are combined with lenses discovered by SLACS in Cycles 13 and 14, we expect the final SLACS lens sample to number 80–100: an approximate doubling of the number of known galaxy-scale strong gravitational lenses and an order-of-magnitude increase in the number of optical Einstein rings. By virtue of its homogeneous selection and sheer size, the SLACS sample will allow an unprecedented exploration of the mass structure of the early-type galaxy population as a function of all other observable quantities. This new sample will be a valuable resource to the astronomical community by enabling qualitatively new strong lensing science, and as such we will waive all but a short {3-month} proprietary period on the observations.


Morphologies of the Most Extreme High-Redshift Mid-IR-Luminous Galaxies

The formative phase of the most massive galaxies may be extremely luminous, characterized by intense star- and AGN-formation. Till now, few such galaxies have been unambiguously identified at high redshift, restricting us to the study of low-redshift ultraluminous infrared galaxies as possible analogs. We have recently discovered a sample of objects which may indeed represent this early phase in galaxy formation, and are undertaking an extensive multiwavelength study of this population. These objects are bright at mid-IR wavelengths {F[24um]>0.8mJy}, but deep ground based imaging suggests extremely faint {and in some cases extended} optical counterparts {R~24-27}. Deep K-band images show barely resolved galaxies. Mid-infrared spectroscopy with Spitzer/IRS reveals that they have redshifts z ~ 2-2.5, suggesting bolometric luminosities ~10^{13-14}Lsun! We propose to obtain deep ACS F814W and NIC2 F160W images of these sources and their environs in order to determine kpc-scale morphologies and surface photometry for these galaxies. The proposed observations will help us determine whether these extreme objects are merging systems, massive obscured starbursts {with obscuration on kpc scales!} or very reddened {locally obscured} AGN hosted by intrinsically low-luminosity galaxies.

FGS 10928

Calibrating Cosmological Chronometers: White Dwarf Masses

We propose to use HST/FGS1R to determine White Dwarf {WD} masses. The unmatched resolving power of HST/FGS1R will be utilized to follow up four selected WD binary pairs. This high precision obtained with HST/FGS1R simply cannot be equaled by any ground based technique. This proposed effort complements that done by CoI Nelan in which a sample of WDs is being observed with HST/FGS1R. This proposal will dramatically increase the number of WDs for which dynamical mass measurements are possible, enabling a better calibration of the WD mass-radius relation, cooling curves, initial to final mass relations, and ultimately giving important clues to the star formation history of our Galaxy and the age of its disk as well as in other galaxies.

NIC1/NIC2/NIC3 8794

NICMOS Post-SAA calibration – CR Persistence Part 5

A new procedure proposed to alleviate the CR-persistence problem of NICMOS. Dark frames will be obtained immediately upon exiting the SAA contour 23, and every time a NICMOS exposure is scheduled within 50 minutes of coming out of the SAA. The darks will be obtained in parallel in all three NICMOS Cameras. The POST-SAA darks will be non-standard reference files available to users with a USEAFTER date/time mark. The keyword ‘USEAFTER=date/time’ will also be added to the header of each POST-SAA DARK frame. The keyword must be populated with the time, in addition to the date, because HST crosses the SAA ~8 times per day so each POST-SAA DARK will need to have the appropriate time specified, for users to identify the ones they need. Both the raw and processed images will be archived as POST-SAA DARKSs. Generally we expect that all NICMOS science/calibration observations started within 50 minutes of leaving an SAA will need such maps to remove the CR persistence from the science images. Each observation will need its own CRMAP, as different SAA passages leave different imprints on the NICMOS detectors.


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


10546 – REAcq (1,2,2) failed to RGA Control At AOS (340/21:38:00) REAcq (1,2,2) scheduled at 340/21:03:59-21:11:27 had failed to RGA control due to QSTOP flag on FGS 1.

OBAD #1 data unavailable due to LOS.

OBAD #2: V1 1.45, V2 -16.24, V3 0.25, RSS 16.30

OBAD MAP: not scheduled

10547 – ACS 779 Fold Mechanism Move was Blocked Status Buffer Message ACS 779 (X2)(Fold mechanism move was blocked) was received at AOS (340/21:38:00). #1: P=0 T=40145, #2: P=0 T=50865. The REAcq at 340/21:03:59 had failed so TDF was down when the fold mechanism move to the SBC position was commanded. The move is blocked and the SBC MAMA HV will remain on. The MAMA HV remaining on is a new feature for ACS FSW CS4.01.

10548 – GSAcq(1,3,3) results in fine lock backup (1,0,1) The GSAcq(1,3,3) scheduled at 341/08:34:19 – 08:42:24 resulted in fine lock backup (1,0,1) using FGS-1 due to (QF3SSLEX) scan step limit exceeded on FGS-3. Pre-acquisition OBADs showed (RSS) attitude correction values of 2463.26 and 4.14 arcseconds. Post-acquisition OBAD/MAP had 3-axis (RSS) value of 8.30 arcseconds.


17961-1 – RMGA Calibration for December 2006


                         SCHEDULED      SUCCESSFUL
FGS GSacq               08                    08
FGS REacq               04                    03
OBAD with Maneuver  26                    26


Flash Report: RMGA Calibration Dec 2006

OPS Request 17969 was successfully executed on December 6, 2006 to perform an RMGA Calibration test. RMGA was powered on at 340/20:40:52. PSEA testmode was executed from 340/21:45 to 340/22:28 to collect RMGA analog drift rate data for bias estimates. This data collection period was about 44 minutes (22 iterations of PSEA testmode) and will be processed by SAC. Assessment will determine if the drift rates have changed enough to warrant a bias update in PSEA configuration memory.

SpaceRef staff editor.