Daily Report #4122

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT #4122

PERIOD COVERED: UT May 25, 2006 (DOY 145)

OBSERVATIONS SCHEDULED

SIGNIFICANT EVENTS: (None)

ACS/WFC 10493

A Survey for Supernovae in Massive High-Redshift Clusters

We propose to measure, to an unprecedented 30% accuracy, the SN-Ia
rate in a sample of massive z=0.5-0.9 galaxy clusters. The SN-Ia rate
is a poorly known observable, especially at high z, and in cluster
environments. The SN rate and its redshift dependence can serve as
powerful discrimiminants for a number of key issues in astrophysics
and cosmology. Our observations will: 1. Put clear constraints on the
characteristic SN-Ia "delay time, " the typical time between the
formation of a stellar population and the explosion of some of its
members as SNe-Ia. Such constraints can exclude entire categories of
SN-Ia progenitor models, since different models predict different
delays. 2. Help resolve the question of the dominant source of the
high metallicity in the intracluster medium {ICM} - SNe-Ia, or
core-collapse SNe from an early stellar population with a top-heavy
IMF, perhaps those population III stars responsible for the early
re-ionization of the Universe. Since clusters are excellent
laboratories for studying enrichment {they generally have a simple
star-formation history, and matter cannot leave their deep
potentials}, the results will be relevant for understanding metal
enrichment in general, and the possible role of first generation stars
in early Universal enrichment. 3. Reveal, via nuclear variability, the
AGN fraction in clusters at this redshift, to be compared with the
field AGN fraction. This will be valuable input for understanding
black-hole demographics, AGN evolution, and ICM energetics. 4.
Potentially discover intergalactic cluster SNe, which can trace the
stripped stellar population at high z.

ACS/WFC 10515

The Unique Star Cluster System of M85

Even with its long history as one of the pillars of modern astronomy,
the study of star clusters has continued to reveal new and surprising
things. Over the past decade, numerous programs with HST have shown
that extragalactic star clusters powerfully probe the processes of
galactic formation, evolution, and destruction. The diversity of star
cluster systems is a testament to the rich variation in galaxy
properties. During the course of the ACS Virgo Cluster Survey, we have
discovered that the early-type galaxy M85 has a system of star
clusters unlike any other galaxy studied to date. Hundreds of star
clusters in M85 are fainter and more extended than typical globular
clusters, and have no local analog. We propose deep optical- infrared
imaging with ACS and NICMOS to obtain ages, metallicities,
luminosities, and sizes of unprecedented precision to characterize
these new star clusters and unravel the evolutionary state of M85 that
gave rise to them.

ACS/WFC 10775

An ACS Survey of Galactic Globular Clusters

We propose to conduct an ACS/WFC imaging survey of Galactic globular
clusters. We will construct the most extensive and deepest set of
photometry and astrometry to-date for these systems reaching a main
sequence mass of ~0.2 solar mass with S/N = 10. We will combine these
data with archival WFPC2 and STIS images to determine proper motions
for the stars in our fields. The resultant cleaned cluster CMDs will
allow us to study a variety of scientific questions. These include
[but are not limited to] 1} the determination of cluster ages and
distances 2} the construction of main sequence mass functions and the
issue of mass segregation 3} the internal motions and dynamical
evolution of globular clusters, and 4} absolute cluster motions,
orbits, and the Milky Way gravitational potential. We anticipate that
the unique resource provided by the proposed treasury archive will
play a central role in the field of globular cluster studies for
decades, with a stature comparable to that of the Hubble Deep Field
for high redshift studies.

ACS/WFC/HRC 10536

What Are Stalled Preplanetary Nebulae? An ACS SNAPshot Survey

Essentially all planetary nebulae {PNs} are aspherical, whereas the
mass-loss envelopes of AGB stars are strikingly spherical. Our
previous SNAPshot surveys of a morphologically unbiased sample of
pre-planetary nebulae {PPNs} -- objects in transition between the AGB
and PN evolutionary phases -- show that roughly half our observed
targets are resolved, with bipolar or multipolar morphologies.
Spectroscopic observations of our sample confirm that these objects
have not yet evolved into planetary nebulae. Thus, the transformation
from spherical to aspherical geometries has already fully developed by
the time these dying stars have become PPNs. Although our current
studies have yielded exciting results, they are limited in two
important ways -- {1} the number of well-resolved objects is still
small {18}, and the variety of morphologies observed relatively
multitudinous, hence no clear trends can yet be established between
morphology and other source properties {e.g., near-IR, far-IR colors,
stellar spectral type, envelope mass}, and {2} the current samples are
strongly biased towards small PPNs, as inferred from their low
60-to-25 micron flux ratios [R{60/25}1]. However, the prototype of
objects with R{60/25}1, the Frosty Leo Nebula, has a puzzlingly large
post-AGB age {almost 10^4 yr} and a fairly cool central star, very
different from the expectations of single-star stellar evolutionary
models. A proposed, but still speculative, hypothesis for such objects
is that the slow evolution of the central star is due to backflow of
material onto the mass-losing star, retarding its evolution towards
the PN phase. This hypothesis has significant consequences for both
stellar and nebular evolution. We therefore propose a survey of PPNs
with R{60/25}1 which is heavily weighted towards the discovery of
such "stalled PPNs". Supporting kinematic observations using long-slit
optical spectroscopy {with the Keck}, millimeter and radio
interferometric observations {with OVRO, VLA & VLBA} are being
undertaken. The results from this survey {together with our previous
work} will allow us to draw general conclusions about the complex
mass-outflow processes affecting late stellar evolution, and will
provide crucial input for theories of post-AGB stellar evolution. Our
survey will produce an archival legacy of long-standing value for
future studies of dying stars.

NIC3/ACS/WFC 10504

Characterizing the Sources Responsible for Cosmic Reionization

Our group has demonstrated the role that massive clusters, acting as
powerful cosmic lenses, can play in constraining the abundance and
properties of low-luminosity star-forming sources beyond z~6; such
sources are thought to be responsible for ending cosmic reionization.
The large magnification possible in the critical regions of
well-constrained clusters brings sources into view that lie at or
beyond the limits of conventional exposures such as the UDF, as well
as those in imaging surveys being undertaken with IRAC onboard
Spitzer. We have shown that the combination of HST and Spitzer is
particularly effective in delivering the physical properties of these
distant sources, constraining their mass, age and past star formation
history. Indirectly, we therefore gain a valuable glimpse to yet
earlier epochs. Recognizing the result {and limitations} of the UDF
exposure, we propose a systematic search through 6 lensing clusters
with ACS and NICMOS for further z~6-7 sources in conjunction with
existing deep IRAC data. Our survey will mitigate cosmic variance and
extend the search both to lower luminosities and, by virtue of the
NICMOS/IRAC combination, to higher redshift. The goal is to count and
characterize representative sources at z~6-10 and to delineate the
redshift range of activity for the planning of future observations.

NICMOS 8791

NICMOS Post-SAA calibration - CR Persistence Part 2

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.

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:
#17767-0 - Modify ROC TC Timer for Batt 5 Cap Test @ 145/19:15z
#17769-0 - Continuous Engineering Recording for Battery # 5 BCT @ 145/21:35z

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSacq 08 08
FGS REacq 05 05
OBAD with Maneuver 22 22

SIGNIFICANT EVENTS: Battery 5 Capacity Test Flash Report

Battery 5 low-rate discharge was completed on Thursday afternoon.
Following approximately 50½ hours of total discharge time, the target
low voltage was reached and the reconditioning resistor was
autonomously turned off by HST486 FSW at 145/1538 GMT (11:38am). EPS
hardware reconfiguration was completed during the orbit night period,
with the reconnection of solar array section 5 to battery 5 occurring
at 145/1629 GMT (12:29pm).

As planned, the Trickle Charge Elapse Timer was increased from 4 to 5
orbits at 145/1625 GMT (12:25pm) to allow for the expected delay in
reaching charge cut-off during the initial orbits of recovery.

Battery 5 is scheduled to be placed back on-line in a 6-Battery FSW
configuration on 146/1440 GMT (Friday at 10:40am).