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10 Apr 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT        # 3338

PERIOD COVERED: DOY 99

Part 1 of 2

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.

STIS/MA2 9096

Objective-Prism Spectroscopy of Massive Young Clusters.

Obtaining STIS NUV-MAMA objective-prism spectroscopy in the 1300-3600
Angstrom range of three nearby extragalactic regions with a total
of ~ 10 MYCs since most of the present knowledge of the UV spectral
properties of massive young clusters {MYCs} is based on IUE data with
marginal spatial resolution. Slitless techniques are seldom attempted
on crowded clusters due to the overlap among different sources. It is
planned to overcome that problem by observing with two different roll
angles, using comparison UV and optical images from the HST archive.

ACS 9363

Ultra Low Surface Brightness Galaxies

Extremely low surface brightness galaxies have been detected in the
Virgo cluster, which are 2 magnitudes fainter than any previously
known in that cluster or even in the Local Group. ACS images of three
of these should resolve stars at the giant branch tip, and allow us
to determine distances, mean metal abundance of the stars, and rough
ages. Confirmation of the nature of these galaxies will provide
evidence that dark matter halos are pervasive in the universe,
extending to galaxies with stellar densities 6 times lower than
currently known. These resolved stars would be the most distant yet
observed accurately by HST. 

STIS/MA2 9465

The Cosmic Carbon Budget

Gaseous carbon drives the chemistry of, and is an important coolant
in interstellar clouds. In solid form, carbon is the second most
abundant element in interstellar dust, the key element contributing
to interstellar extinction, and the dominant heat source in some
interstellar clouds. Given the fundamental importance of this element
to interstellar cloud physics, it is surprising that only 8
measurements of gas- phase carbon abundances exist for neutral
clouds; 7 are in diffuse clouds where the least amount of chemistry
and dust incorporation are expected. The single measurement in a
translucent cloud suggests a C abundance that differs from the
diffuse clouds, but the measurement uncertainties make this
difference statistically insignificant. We, therefore, have no
information about carbon's behavior in translucent clouds, regions
dense enough for chemistry and dust growth to be important but low
enough extinction so that UV spectroscopy is possible {unlike for
molecular clouds}. We propose to measure total gas-phase C abundances
in 6 translucent clouds with our principal scientific goals being to
1} accurately determine the fraction of carbon in the gas and dust
phases in environments bridging the gap between diffuse and molecular
clouds 2} determine the relative depletions of C and O in neutral
clouds with known O-depletion enhancements and 3} explore how the
interstellar gas-phase C/H is related to extinction variations. 

ACS 9480

Cosmic Shear With ACS Pure Parallels

Small distortions in the shapes of background galaxies by foreground
mass provide a powerful method of directly measuring the amount and
distribution of dark matter. Several groups have recently detected
this weak lensing by large-scale structure, also called cosmic shear.
The high resolution and sensitivity of HST/ACS provide a unique
opportunity to measure cosmic shear accurately on small scales. Using
260 parallel orbits in Sloan textiti {F775W} we will measure for the
first time: beginlistosetlength sep0cm setlengthemsep0cm setlength
opsep0cm em the cosmic shear variance on scales <0.7 arcmin, em the
skewness of the shear distribution, and em the magnification effect.
endlist Our measurements will determine the amplitude of the mass
power spectrum sigma_8Omega_m^0.5, with signal-to-noise {s/n} ~ 20,
and the mass density Omega_m with s/n=4. They will be done at small
angular scales where non-linear effects dominate the power spectrum,
providing a test of the gravitational instability paradigm for
structure formation. Measurements on these scales are not possible
from the ground, because of the systematic effects induced by PSF
smearing from seeing. Having many independent lines of sight reduces
the uncertainty due to cosmic variance, making parallel observations
ideal.

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