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15 May 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT        # 3363

PERIOD COVERED: DOY 134

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.

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.

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.

STIS 9441

Zinc Abundances in Damped Ly-Alpha Systems at z < 0.5: A Missing Link
in the Chemical History of Galaxies

The evolution of metallicity in damped Lyman alpha {DLA} quasar
absorption systems is an important constraint on the global star
formation history of the universe, but remains a big puzzle at
present. The H I column density weighted mean metallicity in DLAs is
expected to rise to solar values at low redshifts, based on cosmic
chemical evolution models, because the mass-weighted mean metallicity
of local galaxies is near- solar. However, current DLA abundance
studies are highly uncertain and cannot distinguish between evolution
and no evolution in the mean metallicity at redshifts 0.4 < z < 3.5.
The existing data are particularly incomplete because no Zn
measurements exist for z < 0.4, and only 2 exist for z < 0.5, which
spans the past 35-45 % of the age of the universe. To pin down the
cosmic age-metallicity relation all the way to the present epoch, we
propose to measure Zn abundances in five DLAs at 0.1 < z < 0.5. We
propose to use HST STIS because it is the only existing instrument
that can measure the necessary UV lines. Our observations will
clearly distinguish between no metallicity evolution vs. the
predicted evolution. Our data will also provide Cr measurements,
which will help to estimate the dust abundance. The proposed
observations are crucial for tying together the absorption and
emission histories of gas and stars in galaxies and for clarifying
the relation of DLAs to present-day galaxies.

ACS 9472

A Snapshot Survey for Gravitational Lenses among z >= 4.0 Quasars

Over the last few years, the Sloan Digital Sky Survey has
revolutionized the study of high-redshift quasars by discovering over
200 objects with redshift greater than 4.0, more than doubling the
number known in this redshift interval.  The sample includes eight of
the ten highest redshift quasars known. We propose a snapshot imaging
survey of a well-defined sample of 250 z > 4.0 quasars in order to
find objects which are gravitationally lensed. Lensing models
including magnification bias predict that at least 4% of quasars in a
flux-limited sample at z > 4 will be multiply lensed. Therefore this
survey should find of order 10 lensed quasars at high redshift; only
one gravitationally lensed quasar is currently known at z > 4. This
survey will provide by far the best sample to date of high-redshift
gravitational lenses. The observed fraction of lenses can put strong
constraints on cosmological models, in particular on the cosmological
constant Lambda. In addition, magnification bias can significantly
bias estimates of the luminosity function of quasars and the
evolution thereof; this work will constrain how important an effect
this is, and thereby give us a better understanding of the evolution
of quasars and black holes at early epochs, as well as constrain
models for black hole formation. 

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