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8 May 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT # 3358

PERIOD COVERED: DOY 127

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/WFC 9351

Determining Hubble's Constant from Observations of Cepheids in the
Host Galaxy of SN Ia 1994ae

We propose to determine the luminosity of the type Ia supernova
{SN Ia} 1994ae by observing Cepheids in the host spiral galaxy NGC
3370. Modern CCD photometry has yielded an extremely tight Hubble
diagram for SNe Ia with a precisely determined intercept {i.e., Delta
H_0/H_0} 1 measurement of the true Hubble constant is still limited
by the calibration. The HST calibration of all but a few SNe Ia
observed to date is significantly compromised by the systematics of
photographic photometry and host galaxy extinction, as well as by the
photometric uncertainties associated with WFPC2. In contrast, SN
1994ae is one of the very best-observed SNe Ia with CCD photometry.
The exquisite B, V, R, and I light curves are well-sampled beginning
10 days before maximum brightness, and they indicate little
reddening. From our supernova photometry and the current provisional
SN Ia calibration we would find a distance of 30 +/- 2.1 Mpc, well
within the range where ACS can accurately observe Cepheid light
curves and distinguish Cepheids from nonvariable stars. 

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.

GO 9428

SINS: The Supernova Intensive Study-- Cycle 11

Supernovae create the chemical history of the Universe, energize the
interstellar gas, form the spine of the extragalactic distance scale,
and provide the only direct evidence for an accelerating universe.
SINS is a program to study supernovae, near and far. HST is the
perfect match in field and scale for spatially-resolved observations
of SN 1987A. There, a violent encounter between the fast-moving
debris and the stationary inner ring is well underway. Monitoring
this interaction will help solve the riddles of stellar evolution
posed by the enigmatic three-ring system of SN 1987A. Our UV
observations of Ly-Alpha emission reveal a remarkable reverse shock
that provides a unique laboratory for studying fast shocks and a
powerful tool for dissecting the structure of the vanished star. For
more distant events, we propose Target-of-Opportunity observations.
In addition to one bright new supernova in Cycle 11 discovered by any
search at any time, we propose to discover two supernovae for study
in the ultraviolet at times specified in advance, using the Lick
Observatory Supernova Search. SINS will study the historic SN 1987A,
explore UV emission from supernovae, and press late-time observations
of supernovae into uncharted territory of infrared catastrophes,
light echoes, and stellar remnants.

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.

 - Continued -

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