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14 Apr 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT #3340

PERIOD COVERED: DOYS 101-103

Part 4 of 6

STIS 9509

Probing the Distance and Structure of the LMC Using Eclipsing
Binaries: STIS

The distance to the LMC is crucial to calibrating the Cosmic Distance
Scale but remains controversial and uncertain despite the efforts of
many investigators. We have shown that the analysis of eclipsing
binary {EB} systems has the potential to resolve this controversy. We
have determined accurate distances to three eclipsing binaries in the
LMC. Two EBs in the LMC bar, HV 2274 and EROS 1044, yield a
consistent distance of 46.0+/-1.2 kpc for the bar itself. A third
system, HV 982, is located at a greater distance {50.2+/-1.2 kpc},
which is similar to that of the nearby SN 1987A {51.4+/-1.2 kpc}.
These results may suggest a significant depth to the LMC populations
but a larger stellar sample is needed to verify this. The distances
of the program stars were derived from ground-based light curves, HST
or CTIO radial velocity data, and HST UV/optical spectrophotometry.
We propose HST/STIS low-resolution spectra of seven LMC EBs for which
we already have radial velocity and light curves. This will permit us
to complete the analysis and derive accurate {to ~3%} individual
distances. HST/STIS spectroscopy {covering 115-800nm} is a key
dataset because it provides Teff, Fe/H, and A_lambda. The ensemble of
targets, in addition to nailing down the distance to the LMC, will
provide fundamental stellar properties and a detailed probe of the
structure and spatial extent of this important galaxy, in particular
its line-of-sight depth. 

STIS 9633

STIS parallel archive proposal - Nearby Galaxies - Imaging and
Spectroscopy

Using parallel opportunities with STIS which were not allocated by
the TAC, we propose to obtain deep STIS imagery with both the Clear
{50CCD} and Long-Pass {F28X50LP} filters in order to make
color-magnitude diagrams and luminosity functions for nearby
galaxies. For local group galaxies, we also include G750L slitless
spectroscopy to search for e.g., Carbon stars, late M giants and
S-type stars. This survey will be useful to study the star formation
histories, chemical evolution, and distances to these galaxies. These
data will be placed immediately into the Hubble Data Archive.

STIS 9706

STIS Pure Parallel Imaging Program: Cycle 10

This is the default archival pure parallel program for STIS during
cycle 10.

STIS 9507

STIS/UV snapshot survey of bright AGN

We propose a UV spectroscopic snapshot survey of bright AGN,
quadrupling the number of Seyferts UV spectra and adding dozens of
new quasars, aimed at the following goals: beginenumerate em Finding
the relationship between the intrinsic luminosity of the AGN and the
maximum velocity {and width} of the outflow emanating from it, and
determining the frequency of outflows in low-z AGN as a function of
luminosity. em Surveying IGM absorption line systems in numerous new
sight-lines. em Identifying promising targets for observations with
the future highly sensitive Cosmic Origin Spectrograph. endenumerate
A 35-minute snapshot with exposures in either the G140L or G230L will
yield spectra with a minimum S/N > 15 per resolution element at all
wavelengths for all our potential targets. This will allow us to be
sensitive to absorption lines to a limiting equivalent width of 0.3
Angstrom at the 3 Sigma level. In order to facilitate rapid
observational followup, we waive the data proprietary period
entirely. 

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.

STIS/CCD/MA1 9357

Towards a global understanding of accretion physics --, Clues from an
UV spectroscopic survey of cataclysmic variables

Accretion inflows and outflows are fundamental phenomena in a wide
variety of astrophysical environments, such as Young Stellar Objects,
galactic binaries, and AGN. Observationally, cataclysmic variables
{CVs} are particularly well suited for the study of accretion
processes. We propose to carry out a STIS UV spectroscopic snapshot
survey of CVs that fully exploits the diagnostic potential of these
objects for our understanding of accretion physics. This survey will
provide an homogenous database of accretion disc and wind outflow
spectra covering a wide range of mass transfer rates and binary
inclinations. We will analyse these spectra with state-of-the-art
accretion disc model spectra {SYNDISK}, testing our current knowledge
of the accretion disc structure, and, thereby, providing new insight
into the so far not well understood process of viscous dissipation.
We will use our parameterised wind model PYTHON for the analysis of
the radiation driven accretion disc wind spectra, assessing the
fundamental question whether the mass loss rate correlates with the
disc luminosity. In addition, our survey data will identify a number
of systems in which the white dwarf significantly contributes to the
UV flux, permitting an analysis of the impact of mass accretion on
the evolution of these compact stars. This survey will at least
double, if not triple, the number of high-quality accretion
disc / wind outflow / accreting white dwarf spectra, and we waive our
proprietary rights to permit a timely use of this database. 

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