Daily #3950

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT # 3950

PERIOD COVERED: UT September 21, 2005 (DOY 264)

OBSERVATIONS SCHEDULED

ACS/HRC 10572

Resolving M32's Main Sequence: A Critical Test for Stellar Population
Studies

We propose to observe the M32 main-sequence turnoff {MSTO} with deep
ACS/HRC B and V images. Only the superior resolution and blue
sensitivity of ACS/HRC make this possible. M32 is the only elliptical
galaxy close enough to allow direct observation of its MSTO - it is a
vital laboratory for deciphering the stellar populations of all other
elliptical galaxies, which can only be studied by the spectra of their
integrated light, given their greater distances. Major questions about
M32's star formation history remain unanswered. Spectral studies
suggest that M32 underwent a recent burst of star formation 3 to 8
billion years ago; observation of the M32 MSTO will confirm this
directly. In the process, ACS will easily resolve more luminous
components: hot blue stars, luminous, intermediate-age red clump and
AGB stars, and any extended blue horizontal branch. These detailed
CMDs will provide a direct comparison with population synthesis models
for M32, providing a bridge to studies of the integrated light of more
distant elliptical galaxies, a crucial ingredient for understanding
their star formation histories. As M32 is projected against the edge
of the M31 disk, an essential part of our proposal includes deep
observation of an M31 disk field to allow the M32 photometry to be
background corrected. These observations will reveal the star
formation history of M31's outer disk and are thus of interest in
their own right.

ACS/HRC 10602

A Complete Multiplicity Survey of Galactic O2/O3/O3.5 Stars with ACS

Massive stars are preferentially formed in compact multiple systems
and clusters and many of them remain spatially unresolved to date,
even in our Galaxy. This has hindered the determination of the stellar
upper mass limit. The lack of an accurate knowledge of the
multiplicity of massive stars can also introduce biases in the
calculation of the IMF at its high-mass end. We have recently used
ACS/HRC to resolve HD 93129 A, the earliest O-type star known in the
Galaxy, into a 55 mas binary. We propose here to extend that work into
a complete multi-filter ACS imaging survey of all {20} known
O2/O3/O3.5 Galactic stars to characterize the multiplicity of the most
massive stars. The data will be combined with existing FGS
observations to explore as large a parameter range as possible and to
check for consistency. We will also derive the IMF of each system
using a crowded-field photometry package and processing the data with
CHORIZOS, a code that can derive stellar temperatures, extinctions,
and extinction laws from multicolor photometry.

ACS/WFC 10421

Searching for Ancient Mergers in Early Type Host Galaxies of Classical
QSOs

Recent HST imaging of QSO host galaxies indicates that at least a
large fraction of QSOs reside in seemingly undisturbed elliptical
hosts. However, our deep Keck spectroscopy of a sample of these host
galaxies indicates that many of these objects were involved in a major
starburst episode between 0.6 and 1.6 Gyr ago. We propose to obtain
very deep ACS WFC observations of the five hosts in this sample that
have the most reliable age determinations to search for fine structure
indicative of a past merger event and to test the hypothesis that the
elliptical hosts are the products of relatively recent merger events
rather than old galaxies which formed at high redshifts. By
establishing a firm connection between ancient mergers and the aging
starbursts in these classical QSOs, we will be able to estimate the
fraction of the total QSO population that results directly from
mergers accompanied by massive starbursts and to place constraints on
the duty cycle for QSO activity.

ACS/WFC 10496

Decelerating and Dustfree: Efficient Dark Energy Studies with
Supernovae and Clusters

We propose a novel HST approach to obtain a dramatically more useful
"dust free" Type Ia supernovae {SNe Ia} dataset than available with
the previous GOODS searches. Moreover, this approach provides a
strikingly more efficient search-and-follow-up that is primarily pre-
scheduled. The resulting dark energy measurements do not share the
major systematic uncertainty at these redshifts, that of the
extinction correction with a prior. By targeting massive galaxy
clusters at z 1 we obtain a five-times higher efficiency in
detection of Type Ia supernovae in ellipticals, providing a
well-understood host galaxy environment. These same deep cluster
images then also yield fundamental calibrations required for future
weak lensing and Sunyaev-Zel'dovich measurements of dark energy, as
well as an entire program of cluster studies. The data will make
possible a factor of two improvement on supernova constraints on dark
energy time variation, and much larger improvement in systematic
uncertainty. They will provide both a cluster dataset and a SN Ia
dataset that will be a longstanding scientific resource.

ACS/WFC 10497

Cepheid Calibrations of the Luminosity of Two Reliable Type Ia
Supernovae and a Re- determination of the Hubble Constant

We propose to determine the luminosity of two type Ia supernovae {SNe
Ia}, 1995al in NGC 3021 and SN 2002fk in NGC 1309, by observing
Cepheids in their spiral hosts. Modern CCD photometry yields an
extremely tight Hubble diagram for SNe Ia with a precisely determined
intercept {i.e., Delta H_0/H_0}. Yet, the measurement of the true
Hubble constant via SNe Ia is limited by the calibration derived from
problematic and unreliable SN data. Most of the SNe Ia calibrated by
HST to date are significantly compromised by the systematics of
photographic photometry, high reddening and SN peculiarity, and by the
photometric anomolies associated with WFPC2. The extended reach of ACS
now provides opportunities to more reliably calibrate SNe Ia and H_0.
Our Cepheid calibration of a reliable SN Ia dataset, SN 1994ae, using
ACS in Cycle 11 resulted in a 15% increase in H_0 from the value
derived by the HST SN Ia Calibration Program. Yet, there remains a
terribly small sample of reliable SN Ia data sets on which to base
such a crucial cosmological result. SN 1995al and SN 2002fk are two of
the best observed SNe Ia both with little reddening. They provide two
opportunities to use ACS for placing the calibration of H_0 via SN Ia
on firmer footing and potentially improve its precision.

WFPC2 10356

WFPC2 Cycle 13 Decontaminations and Associated Observations

This proposal is for the monthly WFPC2 decons. Also included are
instrument monitors tied to decons: photometric stability check, focus
monitor, pre- and post-decon internals {bias, intflats, kspots, &
darks}, UV throughput check, VISFLAT sweep, and internal UV flat
check.

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: (None)

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS Gsacq 5 5
FGS Reacq 10 10
OBAD with Maneuver 30 30


SIGNIFICANT EVENTS: (None)