Daily #4031

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT #4031

PERIOD COVERED: UT January 18, 2006 (DOY 018)

OBSERVATIONS SCHEDULED

ACS/HRC 10396

Star Clusters, Stellar Populations, and the Evolution of the Small
Magellanic Cloud

As the closest star forming dwarf galaxy, the SMC is the preferred
location for detailed studies of this extremely common class of
objects. We therefore propose to use the capabilities of ACS, which
provide an improvement by an order of magnitude over what is possible
with ground- based optical imaging surveys that are limited by
confusion anddepth, to measure key stellar population parameters in
the SMC from VI color-magnitude diagrams. Our program focuses on
regions where crowding makes HST essential and includes 7 star
clusters and 7 field star locations. We will measure accurate ages of
the clusters, test stellar evolution models, gain fiducial stellar
sequences to use in fitting the field stars, check the form of the
IMF, and substantially extend the study of RR Lyrae variables in the
key NGC121 SMC globular cluster. The field pointings will allow us to
reconstruct the star formation history, look for enhanced star
formation that is expected when the SMC interacts with the LMC and/or
Milky Way, and compare its main sequence luminosity {and mass}
functions with those of the Milky Way, LMC, and UMi dwarf spheroidal.
This proposal is part of a coordinated HST and ground-based study of
the stellar history and star formation processes in the SMC.

ACS/HRC 10542

Charting the Sparkling Star Formation in NGC346

New, stunning V, I images of the youngest and most massive star
forming region NGC 346, in the Small Magellanic Cloud, have been
recently obtained with the HST/ACS. They reveal a myriad of small
compact clusters: some are still embedded in dust, possibly connected
by gas and dust filaments. We also discover a rich population of
pre-main sequence low mass stars {~3 -0.6 Mo} mainly distributed in
the body of NGC 346 and in these compact clusters, which formed with
the central cluster {~5My ago}, but have not reached the main sequence
yet. The immediate question that emerges is: how did star formation
occur in this region? Is there evidence for an age spread among these
clusters, that could be indicative of sequential star formation? We
are, therefore, requesting an immediate follow up investigation with
the ACS/HRC to perform a comprehensive UV/U study of the ten largest
clusters identified in the NGC 346 region, with the objective of
determining, in combination with the already available deep V, I data,
their mass function, their upper mass cut-off, whether mass
segregation is present, whether there are age variations, and what is
the impact of the stellar feedback, with the final aim to establish
how star formation has occured and progressed in this low metallicity
environment.

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/HRC/WFC 10514

Kuiper Belt Binaries: Probes of Early Solar System Evolution

Binaries in the Kuiper Belt are a scientific windfall: in them we have
relatively fragile test particles which can be used as tracers of the
early dynamical evolution of the outer Solar System. We propose a
Snapshot program using the ACS/HRC that has a potential discovery
efficiency an order of magnitude higher than the HST observations that
have already discovered the majority of known transneptunian binaries.
By more than doubling the number of observed objects in dynamically
hot and cold subpopulations we will be able to answer, with
statistical significance, the question of whether these groups differ
in the abundance of binaries as a result of their particular dynamical
paths into the Kuiper Belt. Today's Kuiper Belt bears the imprints of
the final stages of giant-planet building and migration; binaries may
offer some of the best preserved evidence of that long-ago era.

ACS/HRC/WFC 10729

ACS CCDs daily monitor

This program consists of a set of basic tests to monitor, the read
noise, the development of hot pixels and test for any source of noise
in ACS CCD detectors. The files, biases and dark will be used to
create reference files for science calibration. This programme will be
for the entire lifetime of ACS. Changes from cycle 13:- The default
gain for WFC is 2 e-/DN. As before bias frames will be collected for
both gain 1 and gain 2. Dark frames are acquired using the default
gain {2}. This program cover the period Oct, 2 2005- May, 29-2006. The
second half of the program has a different proposal number: 10758.

ACS/SBC 10259

Planetary nebulae in the SMC: a study of stellar evolution and
populations in an extremely low- metallicity environment

The final phase of the evolution of low- and intermediate-mass stars,
the planetary nebula {PN} ejection, is thought to largely contribute
to the carbon and nitrogen enrichment in galaxies, in particular in
old stellar populations. Stellar generations forming from a carbon-
and nitrogen- enriched medium are a necessary condition for planetary
and life formation. It is essential to understand how stars go through
the process of shedding their chemically-enriched shells, and to test
the predictions of stellar evolution theory on the relationship
between stellar mass and elemental enrichment. Magellanic Cloud PNs
are ideal probes for this study. Their abundances can be directly
related to the mass of the central stars and to that of the stellar
progenitor, without the great {distance and reddening} uncertainties
that affect Galactic PNs. The UV lines are essential for calculating
the abundances of the element related to stellar evolution {C, N, O}
and to progenitor populations {e.g., Ne}. We propose to acquire UV
spectroscopy of the SMC PNs whose morphology and central star
properties has been previously determined by us with HST. We will
derive the {C, N, O} abundance-to-mass relation, and determine the
extent to which the mass of the progenitors of asymmetric PNs exceed
that of symmetric PNs. We will also test the PN luminosity function,
and probe cosmic recycling, in a very low-metallicity environment.

ACS/WFC 10374

ACS photometric Stability

This program consists of three parts. In the first part we will
observe a subset of the ACS white dwarfs with HRC and ACS to verify
repeatability to ~0.2%, because the filter shifts are based on
photometric differences between stars of ~1%. These observations are
also required to establish relative magnitudes of the primary WD
standards at the 0.1% level. Targets should be GD153 and G191B2B,
which seems to have the largest V mag error of ~0.008 mag. One orbit
on the most important filters, including the grism and the prisms,
should be expended with each camera for both stars for a total of 4
orbits. In the second part will observe with HRC and WFC a solar
analog star, P330E, to estimate any shifts in the short and the long
wavelength cutoffs of selected filters. Complete filter bandpasses can
be derived directly from the ratio of grism observations with and
without the filter in place. The grism is on filter wheel 1, while
four filters of interest F330W, F344N, F660N, and F814W are on wheel
2. Each grism observation requires 3 settings: filter alone,
filter+grism, and grism alone. In the third part we obtain high S/N
photometric and spectroscopic observations of three red stars, VB-8
{M7}, 2M0038+18 {L3.5} and 2M0559-14 {T5} with HRC and WFC to verify
the photometry at the new standard position and to obtain accurate
calibration {1% or better} of the grism spectra.

ACS/WFC 10543

Microlensing in M87 and the Virgo Cluster

Resolving the nature of dark matter is an urgent problem. The results
of the MACHO survey of the Milky Way dark halo toward the LMC indicate
that a significant fraction of the halo consists of stellar mass
objects. The VATT/Columbia survey of M31 finds a similar lens fraction
in the M31 dark halo. We propose a series of observations with ACS
that will provide the most thorough search for microlensing toward
M87, the central elliptical galaxy of the Virgo cluster. This program
is optimized for lenses in the mass range from 0.01 to 1.0 solar
masses. By comparing with archival data, we can detect lenses as
massive as 100 solar masses, such as the remnants of the first stars.
These observations will have at least 15 times more sensitivity to
microlensing than any previous survey, e.g. using WFPC2. This is due
to the factor of 2 larger area, factor of more than 4 more sensitivity
in the I-band, superior pixel scale and longer baseline of
observations. Based on the halo microlensing results in the Milky Way
and M31, we might expect that galaxy collisions and stripping would
populate the overall cluster halo with a large number of stellar mass
objects. This program would determine definitively if such objects
compose the cluster dark matter at the level seen in the Milky Way. A
negative result would indicate that such objects do not populate the
intracluster medium, and may indicate that galaxy harassment is not as
vigorous as expected. We can measure the level of events due to the
M87 halo: this would be the best exploration to date of such a lens
population in an elliptical galaxy. Star-star lensing should also be
detectable. About 20 erupting classical novae will be seen, allowing
to determine the definitive nova rate for this giant elliptical
galaxy. We will determine if our recent HST detection of an M87
globular cluster nova was a fluke, or indicative of a 100x higher rate
of incidence of cataclysmic variables and nova eruptions in globulars
than previously believed. We will examine the populations of variable
stars, and will be able to cleanly separate them from microlensing.

S/C 4974

TRTTEST

The Transcient Response Test is for the periodic performance
monitoring of the FGS 2R servo A mechanism.

WFPC2 10777

WFPC2 WF4 Bay 1 Temperature Reduction Test #1

This proposal tests methods to improve WF4 bias level stability by
adjusting some temperatures inside WFPC2. 1 external and 24 internal
orbits.

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:
17629-0 - TRT Trending Test # 10 @ 018/1523z
17631-1 - VTFE Adjustment During Taper Charge (Options 3) @ 018/1645z

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSacq 08 08
FGS REacq 06 06
OBAD with Maneuver 22 22

SIGNIFICANT EVENTS: (None)