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25 April 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT #3349

PERIOD COVERED: DOY 114

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. 

NICMOS 9402

A NICMOS Study of Merging Nuclei in the Toomre Sequence: Finding
Order Amid Chaos

gas clouds and glaring star formation activity. The dynamically
important centers of mass can only be uncovered by imaging at NIR
wavelengths and with the high spatial resolution of HST. We propose a
near-infrared imaging program to inspect the physical processes of
merging at spatial scales of ~100 pc. The Toomre Sequence provides
the best sample of merging galaxies for such a study, because it has
been studied extensively from the ground, and the global properties
are well understood. Our previous Cycle 9 WFPC2 images of the nuclei
have revealed a wealth of information on star forming activity and
dust, but based on those data alone it is impossible to determine the
locations of the current centers of mass. Determining the mass
centers and stellar density profiles is important for understanding
both the kinematics and the dynamical evolution of the nuclei, and
the formation of nuclear density cusps in galaxies. We propose J, H
and K band imaging of the nuclei in early and intermediate stage
mergers in the Toomre Sequence. Because of the much reduced effect of
dust extinction, the near-infrared images are also optimally suited
to searches for nuclear rings and bars around the nuclei.  Combined
with our ongoing Cycle 9 program, these data will provide a detailed
view of the structure and evolution of a sequence of merger nuclei.

STIS 9437

Quantitative Constraints for Massive Star Evolution Models with
Rotation 

Rotation is now recognized as an important physical component in
understanding massive stars. Theory suggests that rotation affects
the lifetimes, chemical yields, stellar evolution tracks, and the
supernova and compact remnant properties {Heger & Langer 2000,
Maeder & Meynet 2000}. In a Cycle 7 program, we proved that
rotational mixing occurs in massive main sequence stars {Venn et al.
2001}. In this proposal, we want to quantitatively test model
predictions and constrain the theory for a better understanding of
massive star evolution. We are requesting HST STIS observations of
the BIII 2066 Angstrom resonance line of seven massive stars in three
young clusters carefully selected from IUE analyses. These stars show
traces of boron depletion, but without nitrogen enrichment; rotation
is the only theory able to explain this abundance pattern. These new
abundances will allow us to test rotating model predictions: that
mixing strength increases with stellar age, mass, and rotation rate.
They will also help to quantitatively constrain the rotational mixing
efficiencies in massive stars. One very high S/N spectrum of a
moderately boron-depleted star is also requested. We wish to measure
its 11B/10B ratio, which is predicted to change as boron is depleted
in the rotating models. This ratio will further confirm rotational
effects and observationally constrain the 10B{p, Alpha} thermonuclear
reaction rate, which is presently highly uncertain.

ACS/WFC/HRC 9445

Gravitational Microlensing in the NGC 3314A-B Galaxy Pair.

The Advanced Camera for Surveys (WFC and HRC) was used to determine
the composition of the dark matter that dominates the masses of
galaxies which is an important unsolved problem.

ACS/NIC 9452

Characterizing the Star Formation History of a Highly Magnified
z=5.6 Lyman Alpha Source

We have located a remarkably faint pair of compact images arising
from a z=5.6 Lyman Alpha emitting source, magnified 33-fold by the
lensing foreground cluster Abell 2218. Keck spectra verify the
lensing hypothesis but fail to locate any UV stellar continuum to
interesting limits, suggesting the object is a 10^6 M_sun source
viewed close to its epoch of formation. We argue the source could
be representative of an abundant population of low mass systems
forming their first stars at z>5, this example becoming visible only
by virtue of the strong gravitational magnification. We seek HST
imaging to provide much tighter constraints on the nature and
distribution of starlight in this intriguing source. ACS will be used
to investigate the spatial extent of UV continuum light on <100 pc
scales also providing the equivalent width of the Lyman Alpha
emission. NIC will be used to measure the slope of the rest-frame
continuum in order to break age and mass degeneracies caused by the
unknown amount of dust extinction. HST uniquely provides the
resolution and sensitivity to gather detailed information on a
remarkable source which may be representative of a population seen in
future surveys with NGST.

ACS 9480

Cosmic Shear With ACS Pure Parallels

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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