Daily # 4180

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 4180

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

OBSERVATIONS SCHEDULED

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.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS: (None)

COMPLETED OPS REQUEST:
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

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSacq 08 08
FGS
REacq 07 07

OBAD with Maneuver 30 30

SIGNIFICANT EVENTS: (None)