Daily Report #4469

Notice: Due to the conversion of some ACS WFC or HRC observations into
WFPC2, or NICMOS observations after the loss of ACS CCD science
capability in January, there may be an occasional discrepancy between
a proposal's listed (and correct) instrument usage and the abstract
that follows it.


HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT***** # 4469

PERIOD COVERED: UT October 16, 2007 (DOY 289)

OBSERVATIONS SCHEDULED

WFPC2 10925

Imaging the Nearest Damped Lyman Alpha Absorbers

We propose to acquire broad-band and H-alpha imaging of three bright,
very nearby host galaxies for damped Ly-alpha absorbers {DLAs}. Our
targets are the only DLA hosts at z 0.03 {i.e., spatial resolutions
of 1.2 kpc}. The purpose of these observations is to discover the
detailed morphology and kinematics and thus the origins of the gas
giving rise to DLAs. While ground-based spectroscopy of DLAs is used
to infer indirectly the evolution of galaxy metallicity and thick disk
kinematics out to z 4, only with HST imaging of the very lowest
redshift DLA galaxies can we discover these relationships directly. In
conjunction with H I 21-cm VLA emission maps, broad-band and H-alpha
images of these DLAs will allow us to determine: {1} the sites of
active star formation in the host galaxies and their relationship to
the QSO sightline, {2} the presence of stellar streams, supernova
shells, or bipolar "superwind" outflows in DLA host galaxies, and {3}
the detailed spiral structure of the host galaxies, which will allow
us to use the lower resolution H I 21-cm emission line images to
determine unambiguous DLA kinematics with respect to the host galaxy
{i.e., is the DLA rotating with the disk?}. Thus, the high resolution
imaging will allow us to correctly interpret the kinematics and
metallicity information provided by the H I 21-cm VLA maps and HST UV
spectroscopy to better inform the high-z results.

WFPC2 11141

White dwarfs in the open star cluster NGC 188

White dwarf cooling sequences represent the only ways in which we can
determine ages of Galactic components such as the disk and the halo,
and they are an independent check on main sequence ages of globular
star clusters. These age measurements rely heavily on theoretical
cooling models, many of which disagree by as much as a few gigayears
for the coolest white dwarfs. Further, observations of the white dwarf
sequence in the super metal- rich open cluster NGC 6791 have found a
white dwarf age several gigayears younger than the accepted cluster
age determined by main-sequence fitting. The white dwarf sequence of
the solar-metallicity, 7-Gyr old open cluster NGC 188 can provide some
much-needed insight into these uncertainties, but previous HST
observations were too shallow to detect the oldest, faintest white
dwarfs in the cluster. We propose deep imaging of two fields at the
center of the cluster with the following goals: {1} To detect the end
of the white dwarf cooling sequence, providing a much-needed empirical
data point for cool white dwarf evolutionary models, {2} to compare
the white dwarf luminosity function of NGC 188 with that of NGC 6791
to determine if the odd white dwarf sequence in the latter cluster is
due to the cluster's high metallicity or due to a shortcoming in
theoretical models, and {3} to determine via photometry the masses of
white dwarfs formed by solar-mass stars, a quantity not yet
empirically measured.

WFPC2 11178

Probing Solar System History with Orbits, Masses, and Colors of
Transneptunian Binaries

The recent discovery of numerous transneptunian binaries {TNBs} opens
a window into dynamical conditions in the protoplanetary disk where
they formed as well as the history of subsequent events which sculpted
the outer Solar System and emplaced them onto their present day
heliocentric orbits. To date, at least 47 TNBs have been discovered,
but only about a dozen have had their mutual orbits and separate
colors determined, frustrating their use to investigate numerous
important scientific questions. The current shortage of data
especially cripples scientific investigations requiring statistical
comparisons among the ensemble characteristics. We propose to obtain
sufficient astrometry and photometry of 23 TNBs to compute their
mutual orbits and system masses and to determine separate primary and
secondary colors, roughly tripling the sample for which this
information is known, as well as extending it to include systems of
two near-equal size bodies. To make the most efficient possible use of
HST, we will use a Monte Carlo technique to optimally schedule our
observations.

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: (None)

COMPLETED OPS NOTES: (None)

************************ SCHEDULED***** SUCCESSFUL

FGS GSacq*************** 04**************** 04
FGS REacq*************** 11**************** 11
OBAD with Maneuver* **** 30**************** 30

SIGNIFICANT EVENTS:

Gyro 2's second flex lead failed on DOY (278) 10/05/07. An increase in
the gyro's heater duty cycle from 10-12% to 26-38% revealed that
additional heater power was compensating for the absence of motor
current. The second flex lead failure was expected. The first flex
lead failed on August 31, 2007, after which Gyro 6 was turned on. The
second flex lead's failure did not impact HST's operation.