Status Report

NASA Hubble Space Telescope Daily Report # 3390

By SpaceRef Editor
June 25, 2003
Filed under , ,





STIS 9130

The iron abundance in the Magellanic Clouds and Bridge

The spectra of early-type main-sequence stars provide excellent probes
of the current chemical composition of galaxies. The physics of their
atmospheres are well understood, while their surfaces will normally be
unaffected by the products of interior nuclear reactions. We have
previously used optical spectra of such targets to map the abundances
of light metals {such as C, N, O, Mg, Si} in our Galaxy, in the
Magellanic Clouds and in a Bridge of material connecting the latter.
However, we have been unable to obtain iron group abundances for the
Magellanic System due to the intrinsic weakness of the optical Fe
II/III spectra and the system’s low metallicity. Here we propose
observations of strong Fe III ultraviolet lines for two Bridge stars,
plus an LMC target. These will be supplemented by AAT and ESO optical
spectroscopy plus HST spectra for two previously observed targets in
the middle of the Bridge and in the SMC. Using non-LTE model
atmosphere and careful differential methods, relative abundances
accurate to 0.1 dex should be achievable. These five stars will allow
us to determine key element abundances and ratios {eg. O/Fe} in both
Clouds and across the Bridge. As well as providing the first detailed
comparison of the Bridge’s metallicity with those of its parent
Clouds, it will clarify the evolutionary history of this system.


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 analyze 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 parameterized 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.

ACS 9401

The ACS Virgo Cluster Survey

We propose the most comprehensive imaging survey to date of
low-redshift, early-type galaxies. Our goal is to exploit the
exceptional imaging capabilities of the ACS by acquiring deep images
— in the SDSS g^ and z^ bandpasses — for 163 E, S0, dE, dE, N and
dS0 galaxies in Virgo, the nearest rich cluster. This extraordinary
dataset would likely constitute one of the principal legacies of HST,
and would have widespread applications for many diverse areas of
astrophysics. Our immediate scientific objectives are threefold: {1}
measure metallicities, ages and radii for the many thousands of
globular clusters {GCs} in these galaxies, and use this information to
derive the protogalactic mass spectrum of each galaxy; {2} measure the
central luminosity and color profile of each galaxy, and use this
information to carry out a completely independent test of the merging
hierarchy inferred from the GCs, with the aid of N-body codes that
simulate the merger of galaxies containing massive black holes; and
{3} calibrate the z^ -band SBF method, measure Virgo’s 3-D structure,
and carry out the definitive study of the GC luminosity function’s
precision as a standard candle. Our proposed Virgo Cluster Survey will
yield a database of unprecedented depth, precision and uniformity, and
will enable us to study the record of galaxy and cluster formation in
a level of detail which will never be possible with more distant

ACS 9420

Intensive Coverage of the Eta Carinae Event in 2003

For a variety of reasons, HST can provide a very special and unique
data set when Eta Car experiences its next spectroscopic event in
mid-2003. Explaining the phenomenon is only part of the motivation.
This star and its ejecta have unique characteristics that make them
important for several branches of astrophysics; and when a
spectroscopic event occurs, it’s like varying the parameters in an
experiment {or rather, set of experiments}. The 2003 event will be the
last chance in the forseeable future to obtain such a data set. Eta
Carinae has extreme parameters; it is mysterious in surprisingly basic
ways; and HST/STIS can gather useful data on it at a terrific rate. As
we explain below, the proposed data set will be valuable in several
independent ways: It will help solve a specific set of current
problems, it will constitute a large and unique archival data base for
both stellar and nebular astrophysics, and it will be well-suited for
educational uses.

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.

ACS 9468

ACS Grism Parallel Survey of Emission- line Galaxies at Redshift z pl 7

We propose an ACS grism parallel survey to search for emission-line
galaxies toward 50 random lines of sight over the redshift interval 0
< z pl 7. We request ACS parallel observations of duration more than
one orbit at high galactic latitude to identify ~ 300 HAlpha
emission-line galaxies at 0.2 pl z pl 0.5, ~ 720 O IILambda3727
emission-line galaxies at 0.3 pl z pl 1.68, and pg 1000 Ly-alpha
emission-line galaxies at 3 pl z pl 7 with total emission line flux
f pg 2* 10^-17 ergs s^-1 cm^-2 over 578 arcmin^2. We will obtain
direct images with the F814W and F606W filters and dispersed images
with the WFC/G800L grism at each position. The direct images will
serve to provide a zeroth order model both for wavelength calibration
of the extracted 1D spectra and for determining extraction apertures
of the corresponding dispersed images. The primary scientific
objectives are as follows: {1} We will establish a uniform sample of
HAlpha and O II emission-line galaxies at z<1.7 in order to obtain
accurate measurements of co-moving star formation rate density versus
redshift over this redshift range. {2} We will study the spatial and
statistical distribution of star formation rate intensity in
individual galaxies using the spatially resolved emission-line
morphology in the grism images. And {3} we will study high-redshift
universe using Ly-alpha emitting galaxies identified at z pl 7 in the
survey. The data will be available to the community immediately as
they are obtained.

ACS/WFPC2 9488

Cosmic Shear – with ACS Pure Parallel Observations

The ACS, with greater sensitivity and sky coverage, will extend our
ability to measure the weak gravitational lensing of galaxy images
caused by the large scale distribution of dark matter. We propose to
use the ACS in pure parallel {non- proprietary} mode, following the
guidelines of the ACS Default Pure Parallel Program. Using the HST
Medium Deep Survey WFPC2 database we have measured cosmic shear at
arc-min angular scales. The MDS image parameters, in particular the
galaxy orientations and axis ratios, are such that any residual
corrections due to errors in the PSF or jitter are much smaller than
the measured signal. This situation is in stark contrast with
ground-based observations. We have also developed a statistical
analysis procedure to derive unbiased estimates of cosmic shear from a
large number of fields, each of which has a very small number of
galaxies. We have therefore set the stage for measurements with the
ACS at fainter apparent magnitudes and smaller, 10 arc-second scales
corresponding to larger cosmological distances. We will adapt existing
MDS WFPC2 maximum likelihood galaxy image analysis algorithms to work
with the ACS. The analysis would also yield an online database similar
to that in

WFPC2 9592

WFPC2 CYCLE 11 Standard Darks

This dark calibration program obtains dark frames every week in order
to provide data for the ongoing calibration of the CCD dark current
rate, and to monitor and characterize the evolution of hot pixels.
Over an extended period these data will also provide a monitor of
radiation damage to the CCDs.

WFPC2 9595


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

WFPC2 9596


This calibration proposal is the Cycle 11 routine internal monitor for
WFPC2, to be run weekly to monitor the health of the cameras. A
variety of internal exposures are obtained in order to provide a
monitor of the integrity of the CCD camera electronics in both bays
{gain 7 and gain 15}, a test for quantum efficiency in the CCDs, and a
monitor for possible buildup of contaminants on the CCD windows.

STIS 9606

CCD Dark Monitor-Part 2

Monitor the darks for the STIS CCD.

STIS 9608

CCD Bias Monitor – Part 2

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

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.

ACS 9674

CCD Daily Monitor

This program consists of basic tests to monitor, the read noise, the
development of hot pixels and test for any source of noise in ACS CCD
detectors. This programme will be executed once a day for the entire
lifetime of ACS.

STIS 9708

STIS Pure Parallel Imaging Program: Cycle 11

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

WFPC2 9709

POMS Test Proposal: WFII parallel archive proposal

This is the generic target version of the WFPC2 Archival Pure Parallel
program. The program will be used to take parallel images of random
areas of the sky, following the recommendations of the 2002 Parallels
Working Group.

STIS 9783

The Ages of Nuclear Star Clusters in Early-type Spiral Galaxies

We propose to obtain STIS G430L spectra of the previously identified
nuclear star cluster in a sample of 16 spiral galaxies of early to
intermediate Hubble type. HST’s spatial resolution is required to
separate the nuclear cluster from the underlying galaxy bulge.
Analysis of the spectra with population synthesis methods will reveal
the cluster ages. We will use the age distribution to constrain the
duty cycle of nuclear cluster formation. Comparison of the results to
those for a larger sample of nuclear clusters in late-type, bulgeless
galaxies will allow us to investigate possible differences between the
formation mechanisms of nuclear clusters in early and late Hubble
types. Such differences might be expected because galaxy bulges show a
dichotomy: in late Hubble types, the surface brightness profiles are
best described by an exponential, while they follow a de Vaucouleurs
law in earlier types. Although the reason for this dichotomy is still
unknown, it is plausible that galaxy bulges have different formation
mechanisms at the two ends of the Hubble sequence. We know that {1}
nuclear cluster formation is linked to the funneling of gas towards
the nucleus via gravitational torques from stellar bars, {2} a nuclear
mass concentration can make bars unstable, and {3} unstable bars can
form bulges. Therefore, the age distribution of nuclear star clusters
contains important clues to the evolution of galaxy centers and
promises new insight into the origin of the Hubble sequence.

ACS 9984

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


Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be
investigated.) None



                            SCHEDULED     SUCCESSFUL    FAILURE TIMES
FGS GSacq                5                          5
FGS REacq                13                        13
FHST Update              13                        13


SpaceRef staff editor.