Daily # 4189

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 4189

PERIOD COVERED: UT August 30, 2006 (DOY 242)

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/HRC/WFC 10737

CCD Stability Monitor

This program will verify that the low frequency flat fielding, the
photometry, and the geometric distortion are stable in time and across
the field of view of the CCD detectors. A moderately crowded stellar
field in the cluster 47 Tuc is observed every three months with the
HRC {at the cluster core} and WFC {6' West of the cluster core} using
the full suite of broad and narrow band imaging filters. The positions
and magnitudes of objects will be used to monitor local and large
scale variations in the plate scale and the sensitivity of the
detectors and to derive an independent measure of the detector CTE. An
additional orbit is required to compare WFC observations taken at gain
1 with those taken at the new default gain 2.

ACS/HRC/WFC 10758

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 May, 31 2006- Oct, 1-2006. The
first half of the program has a different proposal number: 10729.

ACS/WFC 10505

The Onset of Star Formation in the Universe: Constraints from Nearby
Isolated Dwarf Galaxies.

The details of the early star formation histories of tiny dwarf
galaxies can shed light on the role in galaxy formation of the
reionization which occured at high redshift. Isolated dwarfs are ideal
probes since their evolution is not complicated by environmental
effects owing to the vicinity of the Milky Way and M31. In addition,
dwarf galaxies are the most common type of galaxies, and potentially
the building blocks of larger galaxies. Since we can date the oldest
stars in them, their study represents a complementary approach to the
study of the formation and evolution of galaxies through high-z
observations. We propose to use the ACS to obtain a homogeneus dataset
of high-quality photometry, down to the old {13 Gyr} main-sequence
turnoffs, for a representative sample of 4 isolated Local Group dwarf
galaxies. These data are essential to unambiguously determine their
early star formation histories, through comparison with synthetic
color-magnitude diagrams, and using the constraints provided by their
variable stars. Parallel WFPC2 observations of their halos will allow
us to reveal the actual nature of their stellar population gradients,
providing important aditional constraints on their evolution. The
proposed observations are being complemented with ground-based
spectroscopy, to obtain metallicity and kinematic information. The
observations requested here, which must reach M_I=+3.5 {I=27.5- 28.2}
with S/N=10 in crowded systems, can only be achieved with HST using
ACS, and won't be possible with planned ground- or space-based
facilities such as JWST. Based on deep WFPC2 observations and ACS
image simulations, our team has designed an observational strategy
which carefully considers the optimal filter combination, the
necessary photometry depth and the effects of stellar crowding.

ACS/WFC 10630

The Fine Structure of Elliptical Galaxies in Voids

Elliptical galaxies constitute a remarkably homogeneous class of
objects with a tight color- magnitude relation and a well-defined
Fundamental Plane. In spite of their bland and symmetrical morphology,
they are characterized by a wealth of structural features {such as
nuclear disks, dust lanes, shells, blue cores, etc.} which contain
important clues to their formation history. Little is known about how
and if these sub-structures vary as a function of environment; in
fact, due to the morphology density relation, our knowledge of
ellipticals is strongly biased towards overdense regions such as
clusters. But what of the fine structure of ellipticals in voids?
According to theoretical predictions, void galaxies should have
different merger histories than those in clusters, which may imply
that their fine structure also differs. We address these issues using
the exquisite angular resolution of HST/ACS to resolve sub-structures
in the most accurately classified sample, to date, of truly isolated
ellipticals, identified using the 2dFGRS.

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:
17913-0 - Install TRTT macro @ 242/1412z

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSacq 08 08
FGS REacq 05 05
OBAD with Maneuver 26 26

SIGNIFICANT EVENTS: (None)