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24 March 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT       # 3325

PERIOD COVERED: DOYs 80-82

Part 4 of 6

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.

NICMOS 9484

The NICMOS Parallel Observing Program

We propose to manage the default set of pure parallels with NICMOS.
Our experience with both our GO NICMOS parallel program and the
public parallel NICMOS programs in cycle 7 prepared us to make
optimal use of the parallel opportunities. The NICMOS G141 grism
remains the most powerful survey tool for HAlpha emission-line
galaxies at cosmologically interesting redshifts. It is particularly
well suited to addressing two key uncertainties regarding the global
history of star formation: the peak rate of star formation in the
relatively unexplored but critical 1<= z <= 2 epoch, and the amount
of star formation missing from UV continuum-based estimates due to
high extinction. Our proposed deep G141 exposures will increase the
sample of known HAlpha emission- line objects at z ~ 1.3 by roughly
an order of magnitude. We will also obtain a mix of F110W and F160W
images along random sight-lines to examine the space density and
morphologies of the reddest galaxies. The nature of the extremely red
galaxies remains unclear and our program of imaging and grism
spectroscopy provides unique information regarding both the incidence
of obscured star bursts and the build up of stellar mass at
intermediate redshifts. In addition to carrying out the parallel
program we will populate a public database with calibrated spectra
and images, and provide limited ground- based optical and near-IR
data for the deepest parallel fields. 

STIS 9608

CCD Bias Monitor - Part 2

Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at
gain=1, and 1x1  at gain = 4, to build up high-S/N superbiases and
track the evolution of hot columns.

STIS 9606

CCD Dark Monitor-Part 2

Monitor the darks for the STIS CCD.

STIS 9615

Cycle 11 MAMA Dark Monitor

This test performs the routine monitoring of the MAMA detector dark
noise. This proposal will provide the primary means of checking on
health of the MAMA detectors systems through frequent monitoring of
the background count rate. The purpose is to look for evidence of
change in dark indicative of detector problem developing.

STIS 9455

Mid-Ultraviolet Spectral Templates for Old Stellar Systems

We propose a three-year program to provide both observational and
theoretical mid-ultraviolet {2300A -- 3100A} spectral templates for
interpreting the age and metallicity of globular clusters and
elliptical galaxies from spectra of their integrated light. The
mid-UV is the region most directly influenced by stellar age, and is
observed directly in optical and infrared studies of high-redshift
quiescent systems. The reliability of age and metallicity
determinations remains questionable until non-solar metallicities and
abundance ratios are considered, and stars spanning the
color-magnitude diagram are included, as we propose here.

With archival HST STIS spectra we have improved the list of mid-UV
atomic line parameters, then calculated spectra from first principles
which match observed spectra of standard stars up to one- fourth
solar metallicity. We will extend both observations and calculations
to stars of solar metallicity and beyond, and to those in short-lived
stages hotter than the main-sequence turnoff, stars not currently
well-represented in empirical libraries. The necessary line-list
improvements will come from new high-resolution mid-UV spectra of
nine field stars. A key application of the results of this program
will be to the old systems now being discovered as `Extremely Red
Objects' at high redshifts. Reliable age-dating of these places
constraints on the epoch when large structures first formed in the
universe. 

STIS 9417

New Clues to the Origin of the Extreme Helium Stars

The extreme helium stars {EHes} are H-poor supergiants whose origins
are not yet  understood despite thorough analyses of optical spectra.
This proposal seeks STIS echelle spectra for 7 stars from which novel
data on their chemical compositions will be obtained to pin down key
abundances. First, even the EHe's initial metallicity is uncertain;
certain abundance ratios - e.g., Ca/S, Ti/S, and Fe/S - imply
alterations of surface abundances among elements from Na to Ni
resulting from fractionation or diffusive separation, possibly the
result of winnowing of dust grains from gas. The zinc abundance
measurable only from UV spectra will be a powerful clue to the true
metallicity because it is known not to be removed by such winnowing.
Second, elements affected by the s-process, the last of the major
nucleosynthetic processes for which surface abundances are unknown
for EHes, will be studied. The new abundances will be used to probe
the evolutionary origins of these peculiar stars by comparisons with
theoretical scenarios involving a merger of white dwarfs or a final
He-shell flash in a low mass white dwarf, and with observed
abundances for R Coronae Borealis stars that would seem to be close
relatives of the EHes. Spectrophotometric observations of EHes
obtained with GO 8603 will give accurate estimates of effective
temperature and surface gravity that will be used in our abundance
determinations. 

 - Continued -

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