DAILY REPORT #3905

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT #3905

PERIOD COVERED: UT July 19, 2005 (DOY 200)

OBSERVATIONS SCHEDULED

ACS/HRC 10435

Merger-Induced Populations in Early-Type Galaxy Cores

Hierarchical formation models predict that early-type galaxies are
built up over an extended period from mergers of smaller systems, a
process which should leave long- lived signatures in their light
profiles and stellar population colors. Merger events should have
continued up to relatively recent times {the last 1-5 Gyr}, and many
ellipticals and S0 bulges should therefore show evidence of multiple,
discrete, intermediate-age populations. Although there is substantial
observational support for a dissipational merger origin for some
early-type galaxies, most do not exhibit the expected anomalies in
either their light profiles or color distributions. However, existing
searches {mainly in the V and I bands} have not probed very deeply.
Here we propose high resolution, broad-band, near-ultraviolet
{2500-3400 A} imaging of the cores of bright early-type galaxies. This
is the most sensitive probe available for the detection of
spatially-segregated, multiple population components with ages in the
range 1-5 Gyr. Our sample consists of dust- and AGN-free systems with
both normal and mildly anomalous central light profiles. There is very
little existing information on the near-UV structure of early-type
galaxies, and our program would effectively explore new terrain.

ACS/HRC/WFC 10548

Near-UV Snapshot Survey of Low Luminosity AGNs

Low-luminosity active galactic nuclei {LLAGNs} comprise ~30% of all
bright galaxies {B12.5} and are the most common type of AGN. These
include low-luminosity Seyfert galaxies, LINERs, and transition-type
objects {TOs, also called weak-[OI] LINERs}. What powers them is still
at the forefront of AGN research. To unveil the nature of the central
source we propose a near-UV snapshot survey of 50 nearby LLAGNs using
ACS/HRC and the filter {F330W}, a configuration which is optimal to
detect faint star forming regions around their nuclei. These images
will complement optical and near-IR images available in the HST
archive, providing a panchromatic atlas of the inner regions of these
galaxies, which will be used to study their nuclear stellar
population. Our main goals are to: 1} Investigate the presence of
nuclear unresolved sources that can be attributed to an AGN; 2}
Determine the frequency of nuclear and circumnuclear stellar clusters,
and whether they are more common in Transition Objects {TOs} than in
LINERs; 3} Characterize the sizes, colors, luminosities, masses and
ages of these clusters; 4} Derive the luminosity function of star
clusters and study their evaporation over time in the vicinity of
AGNs. Finally, the results of this project will be combined with those
of a previous similar one for Seyfert galaxies in order to compare the
nature of the nuclear sources and investigate if there could be an
evolution from Seyferts to TOs and LINERs. By adding UV images to the
existing optical and near-IR ones, this project will also create an
extremely valuable database for astronomers with a broad range of
scientific interests.

ACS/WFC 10407

When did M31's disk form?

The recent discovery of THIN disk globular clusters in M31 provides a
unique opportunity to determine the age of M31's disk. The globular
cluster kinematics imply that the disk has not been significantly
heated or destroyed by a merger since they were formed. Thus the
cluster ages provide a lower limit to the disk age. This limit will
complement the high-redshift data, where few disk galaxies are
currently known because of their relatively low surface brighness. We
propose to obtain BV ACS imaging of seven disk clusters to below the
level of the horizontal branch {HB} to determine the distribution of
evolved stars in the color-magnitude diagram. The contribution of
evolved stars, particularly blue HB stars, is crucial to estimating
the age of the globular cluster from both color-magnitude diagrams and
the high S/N integrated spectra which we will obtain from the ground.

ACS/WFC 10523

The Halo Shape and Metallicity of Massive Spiral Galaxies

We propose to resolve the stellar populations of the halos of seven
nearby, massive disk galaxies using a SNAP survey with WFC/ACS. These
observations will provide star counts and color-magnitude diagrams 2-3
magnitudes below the tip of the Red Giant Branch along the two
principal axes and one intermediate axis of each galaxy. We will
measure the metallicity distribution functions and stellar density
profiles from star counts down to very low average surface
brightnesses, equivalent to ~31 V-mag per square arcsec. This proposal
will create a unique sampling of galaxy halo properties, as our
targets cover a range in galaxy mass, luminosity, inclination, and
morphology. As function of these galaxy properties this survey will
provide:- the first systematic measurement of radial light profiles
and axial ratios of the diffuse stellar halos and outer disks of
spiral galaxies- a comprehensive analysis of halo metallicity
distributions as function of galaxy type and position within the
galaxy- an unprecedented study of the stellar metallicity and age
distribution in the outer disk regions where the disk truncations
occur- the first comparative study of globular clusters and their
field stellar populations We will use these fossil records of the
galaxy assembly process to test halo formation models within the
hierarchical galaxy formation scheme.

ACS/WFC 10624

Solving the Mystery of the Short-Hard Gamma-Ray Bursts

Eight years after the afterglow detections that revolutionized studies
of the long-soft gamma-ray bursts, not even one afterglow of a
short-hard GRB has been seen, and the nature of these events has
become one of the most important problems in GRB research. The Swift
satellite, expected to be in full operation throughout Cycle 14, will
report few-arcsecond localizations for short-hard bursts in minutes,
enabling prompt, deep optical afterglow searches for the first time.
Discovery and observation of the first short-hard optical afterglows
will answer most of the critical questions about these events: What
are their distances and energies? Do they occur in distant galaxies,
and if so, in which regions of those galaxies? Are they the result of
collimated or quasi- spherical explosions? In combination with an
extensive rapid-response ground-based campaign, we propose to make the
critical high-sensitivity HST TOO observations that will allow us to
answer these questions. If theorists are correct in attributing the
short- hard bursts to binary neutron star coalescence events, then
they will serve as signposts to the primary targeted source population
for ground-based gravitational-wave detectors, and short-hard burst
studies will have a vital role to play in guiding those observations.

ACS/WFC/WFPC2 10394

Deep imaging of newly discovered globular clusters in the outer halo
of M31

Globular clusters {GCs} are fossil relics with which we can
investigate the processes of galaxy formation and growth. We have
recently discovered a sample of GCs, as part of a very wide area CCD
survey of M31. These clusters span a range in projected galactocentric
distance of 20 - 80 kpc, more than double the radii of the previous
most remote known GC. Here we apply for deep ACS images of 13 GCs,
which will allow us to study their stellar populations, line-of-sight
distances and structural parameters. These will be used to: a}
Investigate the merger history of M31, through an examination of
variations in the RGB and HB morphologies, particularly to obtain
metallicities and check for the presence of any second parameter
effect in the HB. d} Determine, in conjuction with ground-based
spectroscopy, the dynamical mass of M31 at large radius, providing a
direct probe of the mass distribution of its dark halo.

ACS/WFC/WFPC2 10402

The Formation and Evolution of Spirals: An ACS and WFPC2 Imaging
Survey of Nearby Galaxies

Over 50% of galaxies in the local universe are spirals. Yet the star
formation histories and evolution of this crucial population remain
poorly understood. We propose to combine archival data with new
ACS/WFC and WFPC2 observations of 11 galaxies, to tackle a
comprehensive investigation of nearby spirals covering the entire
spiral sequence. The new observations will fill a serious deficiency
in HST's legacy, and maximize the scientific return of existing HST
data. The filter combination of UBVI, and Halpha is ideal for studying
stellar populations, dust properties, and the ISM. Our immediate
scientific objectives a {i} to use the resolved cluster
populations, both young massive clusters and ancient globular clusters
as a chronometer, to understand how spirals assembled as a function of
time; {ii} study the rapid disruption properties of young clusters;
and {iii} understand dust distributions in spirals from pc to kpc
scales. Each of these goals provides an important step towards
charting the evolution of galaxies, and an essential baseline for
interpreting the galaxy populations being surveyed in both the early
and present universe. The resolution of our survey, which exploits the
excellent imaging capabilities of HST's two optical cameras, will
enable us to understand the record of star cluster, and galaxy
formation in a level of detail which is not possible for more distant
systems. Finally, the proposed observations will provide a key to
interpret an extensive, multiwavelength archive of space- and ground-
based data at lower spatial resolution {SPITZER, CHANDRA, GALEX,
NICMOS P alpha and H band imaging} for local spirals.

WFPC2 10360

WFPC2 CYCLE 13 INTERNAL MONITOR

This calibration proposal is the Cycle 13 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
{gain 7 and gain 15}, a test for quantum efficiency in the CCDs, and a
monitor for possible buildup of contaminants on the CCD windows.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

#9897 - Reacq(2,1,1) required multiple attempts to reach finelock
@200/0248z REacq(2,1,1) at 201/02:48:24 took 2 attempts to achieve
finelock. The acquisition was successful.

COMPLETED OPS REQUEST:
#17477-0 - GENSLEW for Proposal 10411- Slot#12 @200/1445z
#17478-0 - GENSLEW for Proposal 10411- Slot# 1 @200/1447z
#17479-0 - GENSLEW for Proposal 10411- Slot# 2 @200/1449z
#17480-0 - GENSLEW for Proposal 10411- Slot# 3 @200/1450z

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS Gsacq 06 06
FGS Reacq 09 09
FHST Update 10 10

SIGNIFICANT EVENTS: (None)