Daily Report #4462

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 # 4462

PERIOD COVERED: UT October 04, 2007 (DOY 277)

OBSERVATIONS SCHEDULED

ACS/SBC WFPC2 11175

UV Imaging to Determine the Location of Residual Star Formation in Galaxies
Recently Arrived on the Red Sequence

We have identified a sample of low-redshift {z = 0.04 - 0.10} galaxies that
are candidates for recent arrival on the red sequence. They have red optical
colors indicative of old stellar populations, but blue UV-optical colors
that could indicate the presence of a small quantity of continuing or very
recent star formation. However, their spectra lack the emission lines that
characterize star-forming galaxies. We propose to use ACS/SBC to obtain
high- resolution imaging of the UV flux in these galaxies, in order to
determine the spatial distribution of the last episode of star formation.
WFPC2 imaging will provide B, V, and I photometry to measure the main
stellar light distribution of the galaxy for comparison with the UV imaging,
as well as to measure color gradients and the distribution of interstellar
dust. This detailed morphological information will allow us to investigate
the hypothesis that these galaxies have recently stopped forming stars and
to compare the observed distribution of the last star formation with
predictions for several different mechanisms that may quench star formation
in galaxies.

NIC1/NIC2/NIC3 8795

NICMOS Post-SAA calibration - CR Persistence Part 6

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.

NIC3 11080

Exploring the Scaling Laws of Star Formation

As a variety of surveys of the local and distant Universe are approaching a
full census of galaxy populations, our attention needs to turn towards
understanding and quantifying the physical mechanisms that trigger and
regulate the large-scale star formation rates {SFRs} in galaxies.

WFPC2 11029

WFPC2 CYCLE 15 Intflat Linearity Check and Filter Rotation Anomaly Monitor

Intflat observations will be taken to provide a linearity check: the
linearity test consists of a series of intflats in F555W, in each gain and
each shutter. A combination of intflats, visflats, and earthflats will be
used to check the repeatability of filter wheel motions. {Intflat sequences
tied to decons, visits 1-18 in prop 10363, have been moved to the cycle 15
decon proposal xxxx for easier scheduling.} Note: long-exposure WFPC2
intflats must be scheduled during ACS anneals to prevent stray light from
the WFPC2 lamps from contaminating long ACS external exposures.

WFPC2 11079

Treasury Imaging of Star Forming Regions in the Local Group: Complementing
the GALEX and NOAO Surveys

We propose to use WFPC2 to image the most interesting star-forming regions
in the Local Group galaxies, to resolve their young stellar populations. We
will use a set of filters including F170W, which is critical to detect and
characterize the most massive stars, to whose hot temperatures colors at
longer wavelengths are not sensitive. WFPC2's field of view ideally matches
the typical size of the star-forming regions, and its spatial resolution
allows us to measure individual stars, given the proximity of these
galaxies. The resulting H-R diagrams will enable studies of star-formation
properties in these regions, which cover largely differing metallicities {a
factor of 17, compared to the factor of 4 explored so far} and
characteristics. The results will further our understanding of the
star-formation process, of the interplay between massive stars and
environment, the properties of dust, and will provide the key to interpret
integrated measurements of star-formation indicators {UV, IR, Halpha}
available for several hundreds more distant galaxies. Our recent deep
surveys of these galaxies with GALEX {FUV, NUV} and ground-based imaging
{UBVRI, Halpha, [OIII] and [SII]} provided the identification of the most
relevant SF sites. In addition to our scientific analysis, we will provide
catalogs of HST photometry in 6 bands, matched corollary ground-based data,
and UV, Halpha and IR integrated measurements of the associations, for
comparison of integrated star-formation indices to the resolved populations.
We envisage an EPO component.

WFPC2 11103

A Snapshot Survey of The Most Massive Clusters of Galaxies

We propose the continuation of our highly successful SNAPshot survey of a
sample of 125 very X-ray luminous clusters in the redshift range 0.3-0.7. As
demonstrated by the 25 snapshots obtained so far in Cycle14 and Cycle15
these systems frequently exhibit strong gravitational lensing as well as
spectacular examples of violent galaxy interactions. The proposed
observations will provide important constraints on the cluster mass
distributions, the physical nature of galaxy-galaxy and galaxy-gas
interactions in cluster cores, and a set of optically bright, lensed
galaxies for further 8-10m spectroscopy. All of our primary science goals
require only the detection and characterisation of high-surface-brightness
features and are thus achievable even at the reduced sensitivity of WFPC2.
Because of their high redshift and thus compact angular scale our target
clusters are less adversely affected by the smaller field of view of WFPC2
than more nearby systems. Acknowledging the broad community interest in this
sample we waive our data rights for these observations. Due to a clerical
error at STScI our approved Cycle15 SNAP program was barred from execution
for 3 months and only 6 observations have been performed to date -
reinstating this SNAP at Cycle16 priority is of paramount importance to
reach meaningful statistics.

WFPC2 11129

The Star Formation History of the Fornax Dwarf Spheroidal Galaxy

The Fornax dwarf spheroidal galaxy is one of the most luminous dwarf
satellites of the Milky Way. It is unusual in many ways: it hosts 5 globular
clusters, shows some relatively young stars, and has faint sub-structures
which have been interpreted as signs of recent interactions. It is thus of
great interest to learn the complete star formation history {SFH} of Fornax
to establish a link between its evolutionary path and the predictions from
numerical simulations, as a test of our understanding of dwarf galaxy
evolution. Yet many questions remain open. Is the old stellar population
made up of stars formed in a very early burst, perhaps before the epoch of
reionisation, or the result of a more continuous star formation between 13
and 9 Gyr ago ? How quickly did Fornax increase its metallicity during its
initial assembly and during subsequent episodes of star formation ? Are
accretion episodes required to explain the age-metallicity history of Fornax
? However, there has never been a comprehensive study of the global SFH of
the Fornax field based on data of sufficient depth to unambiguously measure
the age mixture of the stellar populations and their spatial variation. We
propose to use the WFPC2 to obtain very deep images in several fields across
the central region of Fornax in order to reach the oldest main-sequence
turnoffs. The number of fields is determined by the need to measure the SFH
over different regions with distinct kinematics and metallicity. The
resolution achievable with HST is crucial to answer these questions because,
to derive the age distribution of the oldest stars, we are interested in I
magnitude differences of the order 0.2 mag in crowded fields at V=24.5. We
will directly measure the time variation in star-formation rate over the
entire galaxy history, from first stars coeval with the Milky Way halo to
the youngest populations 200 Myr ago. The combination of detailed CMD
analysis with WFPC2 with our existing metallicity and kinematic information
will allow us to trace out the early phases of its evolution.

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 07 07
FGS REacq 06 06
OBAD with Maneuver 26 26

SIGNIFICANT EVENTS: (None)