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26 Mar 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT        # 3327

PERIOD COVERED: DOY 84

Part 2 of 3

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 9476

Galaxy Evolution in the Richest Clusters at z=0.8: the EDisCS Cluster
Sample

The study of distant cluster galaxies requires two key ingredients:
{1} deep high-resolution imaging, to constrain galaxy structure; and
{2} 8m-class spectroscopy, to measure stellar content, star-formation
rates, dynamics, and cluster membership. We will reach both
conditions with the addition of HST/ACS imaging to our suite of VLT
{36 nights} and NTT {20 nights} observations of 10 confirmed clusters
at z~0.8, drawn from the ESO Distant Cluster Survey {EDisCS}.

The proposed HST/ACS data will complement our existing optical/IR
imaging and spectroscopy with quantitative measures of cluster galaxy
morphologies {i.e. sizes and shapes, bulge-disk decompositions,
asymmetry parameters}, and with measurements of cluster masses via
weak lensing. Major advantages unique to the EDisCS project include:
{i} uniform selection of clusters; {ii} large enough sample sizes to
characterize the substantial cluster-to-cluster variation in galaxy
populations; {iii} large quantities of high quality data from 8m
telescopes; {iv} uniform measurements of morphologies, spectroscopic
and photometric redshifts, SEDs, star-formation/AGN activities, and
internal kinematics; {v} optical selection of clusters to complement
the X-ray selection of almost all high-z clusters in the ACS GTO
programs; {vi} forefront numerical simulations designed specifically
to allow physical interpretation of observed differences between the
high-z and local clusters.

ACS 9480

Cosmic Shear With ACS Pure Parallels

Small distortions in the shapes of background galaxies by foreground
mass provide a powerful method of 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.

NICMOS 9485

Completing A Near-Infrared Search for Very Low Mass Companions to
Stars within 10 pc of the Sun

Most stars are fainter and less massive than the Sun. Nevertheless,
our knowledge of very low mass {VLM} red dwarfs and their brown dwarf
cousins is quite limited. Unknown are the true luminosity function
{LF}, multiplicity fraction, mass function, and mass-luminosity
relation for red and brown dwarfs, though they dominate the Galaxy in
both numbers and total mass. The best way to constrain these
relations is a search for faint companions to nearby stars. Such a
search has several advantages over field surveys, including greater
sensitivity to VLM objects and the availability of precise parallaxes
from which luminosities and masses can be derived. We propose to
complete our four-filter NICMOS snapshot search for companions to
stars within 10 pc. With a 10 sigma detection limit of M_J ~ 20 at 10
pc, we can detect companions between 10 and 100 AU that are at least
9 mag fainter than the empirical end of the main sequence and at
least 6.5 mag fainter than the brown dwarf Gl 229B. When completed,
our search will be the largest, most sensitive, volume-limited search
for VLM companions ever undertaken. Our four-filter search will
permit unambiguous identification of VLM-companion candidates for
follow-up observation. Together with IR speckle and deep imaging
surveys, our program will firmly establish the LF for VLM companions
at separations of 1-1000 AU and the multiplicity fraction of all
stars within 10 pc.

STIS 9505

The Evolution of Molecular Clouds.

The combined STIS, FUSE and ground-based results will yield
information needed to understand the role of ablation in the
evolution of the central clouds.

WFPC2 9594

WFPC2 CYCLE 11 SUPPLEMENTAL DARKS pt2/3

This dark calibration program obtains 3 dark frames every day to
provide data for monitoring and characterizing the evolution of hot
pixels

STIS 9606

CCD Dark Monitor-Part 2

Monitor the darks for the STIS CCD.

 - Continued -

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