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18 April 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT #3344

PERIOD COVERED:  DOY 107

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. 

STIS/CCD/MA1 9184

A Survey for Missing Baryons in Highly Ionized Intergalactic Gas at
Low Redshift.

With the STIS FUV E140M echelle mode {7 km s^-1 resolution}.
Combined with archival data, this will increase the sample redshift
path by a factor of ~7 compared to the published data.  With the
echelle data, we will {1} measure the number of O VI absorbers per
unit redshift {dN/dz} and their minimum cosmological mass density
with a limiting equivalent width of W_Lambda ~50 mAngstrom , {2}
examine whether the O VI absorption arises in photoionized,
collisionally ionized, or multiphase gas, and {3} study the
dependence of the O VI system properties on environment.  In addition
to testing this prediction regarding the location of the missing
baryons, the data will have applications to many other topics such as
low-z LyAlpha absorbers and the physical properties and abundances of
gas in the Milky Way halo.

ACS 9352

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

Type Ia supernovae {SNe Ia} provide the only direct evidence for an
accelerating universe, an 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. 

ACS 9401

The ACS Virgo Cluster Survey

We propose the most comprehensive imaging survey to date of
low-redshift, early-type galaxies. Our goal is to exploit the
exceptional imaging capabilities of the ACS by acquiring deep
images --- in the SDSS g^ and z^ bandpasses --- for 163 E, S0, dE,
dE, N and dS0 galaxies in Virgo, the nearest rich cluster. This
extraordinary dataset would likely constitute one of the principal
legacies of HST, and would have widespread applications for many
diverse areas of astrophysics. Our immediate scientific objectives
are threefold: {1} measure metallicities, ages and radii for the many
thousands of globular clusters {GCs} in these galaxies, and use this
information to derive the protogalactic mass spectrum of each
galaxy; {2} measure the central luminosity and color profile of each
galaxy, and use this information to carry out a completely
independent test of the merging hierarchy inferred from the GCs, with
the aid of N-body codes that simulate the merger of galaxies
containing massive black holes; and {3} calibrate the z^ -band SBF
method, measure Virgo's 3-D structure, and carry out the definitive
study of the GC luminosity function's precision as a standard candle.
Our proposed Virgo Cluster Survey will yield a database of
unprecedented depth, precision and uniformity, and will enable us to
study the record of galaxy and cluster formation in a level of detail
which will never be possible with more distant systems.

NICMOS 9423

NICMOS Observations of Transient Infrared Jets in the Galactic
Microquasar GRS1915+105

We propose to use HST/NICMOS to make Target of Opportunity
observations of the galactic microquasar GRS1915+105. This source
possesses transient radio jets which exhibit apparent superluminal
motions, and resolved infrared emission from these jets has been
observed in GRS1915+105 {Sams, Eckart, and Sunyaev, 1996; Eikenberry
and Fazio, 1996}. Because the jet ejection events are correlated with
X-ray outbursts, we will use observations of X-ray flares with the
Rossi X-Ray Timing Explorer to trigger the HST observations. We will
then monitor GRS1915+105 periodically with NICMOS, obtaining relative
astrometry, photometry, polarimetry, and grism spectroscopy of the
jets and the parent object. These observations will allow us to
greatly increase our understanding of the jets' radiative mechanisms
and physical conditions, and their evolution with time. We require
the capabilities of HST and NICMOS due to the small angular
separations between the jets and the parent object {increasing from
~ 0.1 to ~ 0.8 arcsec over the span of the TOO observations} and the
high reddening towards GRS1915+105 {A_V ~ 30 mag}.

 - Continued -

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