Daily # 4188

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 4188

PERIOD COVERED: UT August 29, 2006 (DOY 241)

OBSERVATIONS SCHEDULED

ACS/HRC 10556

Neutral Gas at Redshift z=0.5

Damped Lyman-alpha systems {DLAs} are used to track the bulk of the
neutral hydrogen gas in the Universe. Prior to HST UV spectroscopy,
they could only be studied from the ground at redshifts z1.65.
However, HST has now permitted us to discover 41 DLAs at z1.65 in our
previous surveys. Followup studies of these systems are providing a
wealth of information about the evolution of the neutral gas phase
component of the Universe. But one problem is that these 41
low-redshift systems are spread over a wide range of redshifts
spanning nearly 70% of the age of the Universe. Consequently, past
surveys for low-redshift DLAs have not been able to offer very good
precision in any small redshift regime. Here we propose an ACS-HRC-
PR200L spectroscopic survey in the redshift interval z=[0.37, 0.7]
which we estimate will permit us to discover another 41 DLAs. This
will not only allow us to double the number of low-redshift DLAs, but
it will also provide a relatively high-precision regime in the
low-redshift Universe that can be used to anchor evolutionary studies.
Fortunately DLAs have high absorption equivalent width, so
ACS-HRC-PR200L has high-enough resoultion to perform this proposed
MgII-selected DLA survey.

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.

ACS/WFC 10829

Secular Evolution at the End of the Hubble Sequence

The bulgeless disk galaxies at the end of the Hubble Sequence evolve
at a glacial pace relative to their more violent, earlier-type
cousins. The causes of their internal, or secular evolution are
important because secular evolution represents the future fate of all
galaxies in our accelerating Universe and is a key ingredient to
understanding galaxy evolution in lower-density environments at
present. The rate of secular evolution is largely determined by the
stability of the cold ISM against collapse, star formation, and the
buildup of a central bulge. Key diagnostics of the ISM's stability are
the presence of compact molecular clouds and narrow dust lanes.
Surprisingly, edge-on, pure disk galaxies with circular velocities
below 120 km/s do not appear to contain such dust lanes. We propose to
obtain ACS/WFC F606W images of a well-selected sample of extremely
late-type disk galaxies to measure the characteristic scale size of
the cold ISM and determine if they possess the unstable, cold ISM
necessary to drive secular evolution. Our sample has been carefully
constructed to include disk galaxies above and below the critical
circular velocity of 120 km/s where the dust properties of edge-on
disks change so remarkably. We will then use surface brightness
profiles to search for nuclear star clusters and pseudobulges, which
are early indicators that secular evolution is at work, as well as
measure the pitch angle of the dust lanes as a function of radius to
estimate the central mass concentrations.

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.

WFPC2 10745

WFPC2 CYCLE 14 INTERNAL MONITOR

This calibration proposal is the Cycle 14 routine internal monitor for
WFPC2, to be run weekly to monitor the health of the cameras. A
variety of internal exposures are obtained in order to provide a
monitor of the integrity of the CCD camera electronics in both bays
{both gain 7 and gain 15 -- to test stability of gains and bias
levels}, a test for quantum efficiency in the CCDs, and a monitor for
possible buildup of contaminants on the CCD windows. These also
provide raw data for generating annual super-bias reference files for
the calibration pipeline.

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:

10412 - GSAcq(2,1,1) Failed to RGA Control

GSAcq(2,1,1) scheduled at 242/01:45:37 - 01:53:41 was observed to have
failed to RGA Hold, due to STOP flag indication on
FGS-2.Pre-acquisition OBADs (RSS) attitude corrections values not
available due to LOS. Post-acquisition OBAD/MAP at 242/01:53:40 had
3-axis (RSS) error correction value of 11.08 arcseconds.

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSacq 10 09
FGS REacq 05 05
OBAD with Maneuver 30 30

SIGNIFICANT EVENTS: (None)