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Daily #4030



 
 
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Old January 18th 06, 04:33 PM posted to sci.astro.hubble
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Default Daily #4030

HUBBLE SPACE TELESCOPE - Continuing to collect World Class Science

DAILY REPORT #4030

PERIOD COVERED: UT January 17, 2006 (DOY 017)

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 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 10564

Resolving Ultracool White Dwarf Binaries

We propose an ACS/HRC imaging survey of the coolest white dwarfs known
in order to search for binarity. Current models fail to match observed
spectral energy distributions of these sub- 4000K stellar remnants,
consistently predicting much lower luminosities than observed. A
possible explanation is that they are binary in nature. Because these
cool degenerates have no spectral features, the only way to
investigate their apparent overluminosity is with very high resolution
imaging, which can only be done with HST {these stars are far too
faint to be observed with adaptive optics on the ground}. Optical
wavelengths are ideal because the spectral energy distributions of
these old degenerates peak near 600 nm. With the F435W filter we will
be able to partially resolve equally luminous binaries as close as
0.02", which corresponds to within 0.6 AU for over half of the 12
proposed target stars. The collected data will be critical in
determining whether these stars represent the oldest white dwarfs in
the solar neighborhood.

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 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.

ACS/WFC 10587

Measuring the Mass Dependence of Early-Type Galaxy Structure

We propose two-color ACS-WFC Snapshot observations of a sample of 118
candidate early- type gravitational lens galaxies. Our lens-candidate
sample is selected to yield {in combination with earlier results} an
approximately uniform final distribution of 40 early-type strong
lenses across a wide range of masses, with velocity dispersions {a
dynamical proxy for mass} ranging from 125 to 300 km/s. The proposed
program will deliver the first significant sample of low-mass
gravitational lenses. All of our candidates have known lens and source
redshifts from Sloan Digital Sky Survey data, and all are bright
enough to permit detailed photometric and stellar- dynamical
observation. We will constrain the luminous and dark-matter mass
profiles of confirmed lenses using lensed-image geometry and
lens-galaxy structural/photometric measurements from HST imaging in
combination with dynamical measurements from spatially resolved
ground-based follow-up spectroscopy. Hence we will determine, in
unprecedented detail, the dependence of early-type galaxy mass
structure and mass-to-light ratio upon galaxy mass. These results will
allow us to directly test theoretical predictions for halo
concentration and star-formation efficiency as a function of mass and
for the existence of a cuspy inner dark- matter component, and will
illuminate the structural explanation behind the fundamental plane of
early-type galaxies. The lens-candidate selection and confirmation
strategy that we propose has been proven successful for high-mass
galaxies by our Cycle 13 Snapshot program {10174}. The program that we
propose here will produce a complementary and unprecedented lens
sample spanning a wide range of lens-galaxy masses.

NICMOS 8790

NICMOS Post-SAA calibration - CR Persistence Part 1.

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.

WFPC2 10745

WFPC2 CYCLE 14 INTERNAL MONITOR

This calibration proposal is the Cycle 14 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
{both gain 7 and gain 15 -- to test stability of gains and bias
levels}, a test for quantum efficiency in the CCDs, and a monitor for
possible buildup of contaminants on the CCD windows. These also
provide raw data for generating annual super-bias reference files for
the calibration pipeline.

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

10089 - ReAcq(1,2,1) results in FLBU (2,0,2) due to F1SSLEx @ 009/16:32:33z

OTA SE review of the PTAS processing log for the Q008 SMS run reveals
that the ReAcq starting at 2005.009/16:28:22 resulted in FLBU due to
scan step limit exceeded on FGS1. This was the 3rd of 5 consecutive
Acquisitions (2 Acqs + 3 ReAcqs) using the same guide star pair. None
of the other acquisitions were anomalous.

COMPLETED OPS REQUEST:
17621-2 - VTFE Adjustment During Taper Charge (Options 1) @ 017/1336z

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSacq 09 09
FGS REacq 06 06
OBAD with Maneuver 24 24

SIGNIFICANT EVENTS: (None)


 




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