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23 April 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT     #3347

PERIOD COVERED:  DOY 112

Part 1 of 3

OBSERVATIONS SCHEDULED

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. 

WFPC2 9033

Measuring the mass distribution in the most distant, very X-ray
luminous galaxy cluster known distribution in the massive, distant
galaxy cluster ClJ1226.9+3332, recently discovered by us. At z=0.888
this exceptional system is more X-ray luminous and more distant than
both MS1054.4-0321 and ClJ0152.7-1357, the previous record holders,
thus providing yet greater leverage for cosmological studies of
cluster evolution. ClJ1226.9+3332 differs markedly from all other
currently known distant clusters in that it exhibits little
substructure and may even host a cooling flow, suggesting that it
could be the first cluster to be discovered at high redshift that
is virialized. We propose joint HST and Chandra observations to
investigate the dynamical state of this extreme object. This project
will 1} take advantage of HST's superb resolution at optical
wavelengths to accurately map the mass distribution within 1.9 h^{-1}
50 Mpc via strong and weak gravitational lensing, and 2} use
Chandra's unprecedented resolution in the X-ray waveband to obtain
independent constraints on the gas and dark matter distribution in
the cluster core, including the suspected cooling flow region. As a
bonus, the proposed WFPC2 observations will allow us to test the
results by van Dokkum et al. {1998, 1999} on the properties of
cluster galaxies {specifically merger rate and morphologies} at z~0.8
from their HST study of MS1054.4-0321.

ACS 9352

The Deceleration Test from Treasury Type Ia Supernovae at Redshifts
1.2 to 1.6

Extraordinary result that needs a rigorous test. The case for cosmic
acceleration rests on the observation that SNe Ia at z ~ 0.5 are
~ 0.25 mag fainter than they would be in a universe without
acceleration. A powerful and straightforward way to assess the
reliability of the SN Ia measurement and the conceptual framework of
its interpretation is to look for cosmic deceleration at z >= 1. This
would be a clear signature of a mixed dark-matter and dark-energy
universe. Systematic errors in the SN Ia result attributed to grey
dust or cosmic evolution of the SN Ia peak luminosity would not show
this change of sign. We have demonstrated proof of this concept with
a single SN Ia, SN 1997ff at z = 1.7, found and followed by HST. The
results suggest an early epoch of deceleration, but this is too
important a conclusion to rest on just one object. Here we propose to
use HST for observations of six SNe Ia in the range 1.2 <= z <= 1.6,
that will be discovered as a byproduct from proposed Treasury
programs for high-latitude ACS surveys. Six objects will provide a
much firmer foundation for a conclusion that touches on important
questions of fundamental physics. 

NICMOS 9386

Infrared Photometry of a Statistically Significant Sample of KBOs

While the discovery rate of Kuiper Belt objects is accelerating, the
physical study of this new region of the solar system has been slowed
by a lack of basic astrophysical data. Photometric observations of
the majority of the more than 400 known KBOs and Centaurs are
rudimentary and incomplete, particularly  in the infrared. The
multicolor optical-infrared photometry that exists for a small subset
of KBOs  often shows significant discrepancies between observations
by different observers. Their intrinsic faintness puts them at the
practical limits of ground-based systems. In July 2001 we began what
will be the largest uniform sample of optical photometry of KBOs
with a WFPC2 SNAPSHOT program that will perform accurate photometry
at V, R, and I on a sample of up to 150 targets. We seek to greatly
enhance the value of this survey by obtaining J and H photometry on
the same sample using NICMOS. Combined optical and infrared broad
band photometry is a far more powerful tool for physical studies than
is either alone. Our sample includes objects that will be observed
at thermal infrared wavelengths by SIRTF and will be used with those
data to derive the first accurate diameters, albedos, and surface
properties for a large sample of KBOs.

ACS/WFC/HRC 9445

Gravitational Microlensing in the NGC 3314A-B Galaxy Pair.

The Advanced Camera for Surveys (WFC and HRC) was used to determine
the composition of the dark matter that dominates the masses of
galaxies which is an important unsolved problem.

 - Continued -

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