Status Report

NASA Hubble Space Telescope Daily Status Report #4180

By SpaceRef Editor
August 18, 2006
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NASA Hubble Space Telescope Daily Status Report #4180

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science


PERIOD COVERED: UT August 17, 2006 (DOY 229)


ACS/HRC 10860

The largest Kuiper belt object

The past year has seen an explosion in the discoveries of Pluto-sized objects in the Kuiper belt. With the discoveries of the methane-covered 2003 UB313 and 2005 FY9, the multiple satellite system of 2003 EL61, and the Pluto-Charon analog system of Orcus and its satellite, it is finally apparent that Pluto is not a unique oddball at the edge of the solar system, but rather one of a family of similarly large objects in the Kuiper belt and beyond. HST observations over the past decade have been critical for understanding the interior, surface, and atmosphere of Pluto and Charon. We propose here a comprehensive series of observations designed to similarly expand our knowledge of these recently discovered Pluto-sized and near-Pluto-sized Kuiper belt objects. These observations will measure objects’ sizes and densities, explore the outcome of collisions in the outer solar system, and allow the first ever look at the interior structure of a Kuiper belt object. Our wide field survey that discovered all of these objects is nearly finished, so after five years of continuous searching we are finally almost complete in our tally of these near-Pluto-sized objects. This large HST request is the culmination of this half-decade search for new planetary-sized objects. As has been demonstrated repeatedly by the approximately 100 previous orbits devoted to the study of Pluto, only HST has the resolution and sensitivity for detailed study of these distant objects. With these new Pluto-sized objects only now being discovered we have a limited window left to still use HST for these critical observations.

ACS/SBC 10184

A New Class of Bright Ultraviolet Variable Sources in the Globular Cluster NGC 1851

Our reductions of archival STIS/FUV-MAMA data {AR9225} have discovered 13 completely unexpected and unexplained Ultraviolet bright variables. Eleven of the variables have been identified with evolved stars {Horizontal Branch or Asymptotic Giant Branch}. The total number and nature of these systems is completely unknown. If these variables are binaries the implication is that the binary fraction {up to 25%} in NGC 1851 is the highest in all Galactic globular clusters. The radial distributions of the variables and the blue horizontal branch stars imply a common origin and perhaps an explanation of the bi-modal morphology of the horizontal branch in the color magnitude diagrams of globular clusters. These variables may be the tip of the iceberg and a critical clue concerning the infamous “second parameter”. We propose to observe NGC 1851 on three occasions with the same setup as the archival data to determine the total number and periods of the ultraviolet variables.

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 10421

Searching for Ancient Mergers in Early Type Host Galaxies of Classical QSOs

Recent HST imaging of QSO host galaxies indicates that at least a large fraction of QSOs reside in seemingly undisturbed elliptical hosts. However, our deep Keck spectroscopy of a sample of these host galaxies indicates that many of these objects were involved in a major starburst episode between 0.6 and 1.6 Gyr ago. We propose to obtain very deep ACS WFC observations of the five hosts in this sample that have the most reliable age determinations to search for fine structure indicative of a past merger event and to test the hypothesis that the elliptical hosts are the products of relatively recent merger events rather than old galaxies which formed at high redshifts. By establishing a firm connection between ancient mergers and the aging starbursts in these classical QSOs, we will be able to estimate the fraction of the total QSO population that results directly from mergers accompanied by massive starbursts and to place constraints on the duty cycle for QSO activity.

ACS/WFC 10551

Gamma-Ray Bursts from Start to Finish: A Legacy Approach

The progenitors of long-duration GRBs are now known to be massive stars. This result lends credence to the collapsar model, where a rotating massive star ends its life leaving a black hole or a highly magnetized neutron star, and confirms its essential aspects. The focus of attention now is on the black hole or magnetar engines that power the bursts. Somehow these engines create the most highly relativistic and highly collimated outflows that we know of, through mechanisms that no current theory can explain. These astrophysical laboratories challenge our understanding of relativistic shocks, of mechanisms for extracting energy from a black hole, and of how physics works in extreme conditions. The launch of Swift is bringing us into a new era, where we can make broadband observations that will enable us to study these fascinating physical processes. We propose here an ambitious, comprehensive program to obtain the datasets that will become the standard that any successful model for the central engine must explain. This programs leverages the HST observations to the maximum extent by our commitment of Swift observations, a Large program at the VLA, and extensive ground-based optical resources. By studying the engines and searching for jets in a variety of events, this program will investigate the conditions necessary for the engine and jet formation itself.

FGS 10989

Astrometric Masses of Extrasolar Planets and Brown Dwarfs

We propose observations with HST/FGS to estimate the astrometric elements {perturbation orbit semi-major axis and inclination} of extra-solar planets orbiting six stars. These companions were originally detected by radial velocity techniques. We have demonstrated that FGS astrometry of even a short segment of reflex motion, when combined with extensive radial velocity information, can yield useful inclination information {McArthur et al. 2004}, allowing us to determine companion masses. Extrasolar planet masses assist in two ongoing research frontiers. First, they provide useful boundary conditions for models of planetary formation and evolution of planetary systems. Second, knowing that a star in fact has a plantary mass companion, increases the value of that system to future extrasolar planet observation missions such as SIM PlanetQuest, TPF, and GAIA.


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

HSTARS: (None)


  • 17894-0 – Genslew for proposal 10896 – slot 1 @ 229/16;43z
  • 17895-0 – Genslew for proposal 10896 – slot 2 @ 229/16:44z
  • 17896-0 – Genslew for proposal 10896 – slot 3 @ 229/16:46z


                           SCHEDULED      SUCCESSFUL
FGS GSacq                08                     08
REacq                07                     07 

OBAD with Maneuver  30                     30


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