Status Report

NASA Hubble Space Telescope Daily Report # 3625

By SpaceRef Editor
June 4, 2004
Filed under , ,

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science




ACS 9472

A Snapshot Survey for Gravitational Lenses among z >= 4.0 Quasars

Over the last few years, the Sloan Digital Sky Survey has
revolutionized the study of high-redshift quasars by discovering over
200 objects with redshift greater than 4.0, more than doubling the
number known in this redshift interval. The sample includes eight of
the ten highest redshift quasars known. We propose a snapshot imaging
survey of a well-defined sample of 250 z > 4.0 quasars in order to
find objects which are gravitationally lensed. Lensing models
including magnification bias predict that at least 4% of quasars in a
flux-limited sample at z > 4 will be multiply lensed. Therefore this
survey should find of order 10 lensed quasars at high redshift; only
one gravitationally lensed quasar is currently known at z > 4. This
survey will provide by far the best sample to date of high-redshift
gravitational lenses. The observed fraction of lenses can put strong
constraints on cosmological models, in particular on the cosmological
constant Lambda. In addition, magnification bias can significantly
bias estimates of the luminosity function of quasars and the evolution
thereof; this work will constrain how important an effect this is, and
thereby give us a better understanding of the evolution of quasars and
black holes at early epochs, as well as constrain models for black
hole formation.


Stability of the ACS CCD: Flat fielding, Photometry, Geometry

This program will verify that the low frequency flat fielding, the
photometry, and the geometric distortion are stable in time and across
the field of view of the CCD detectors. A moderately crowded stellar
field, located ~6′ West of the center of the cluster 47 Tuc, is
observed every three months with the WFC and HRC using the full suite
of broad and narrow band filters. The same field has been observed
during SMOV to derive low frequency corrections to the ground flats
and to create a master catalogue of positions and magnitudes from
dithered observations of the cluster. In Cycle 11, this field was
observed again using single pointings at various roll angles. The
positions and magnitudes of objects are used to monitor local and
large scale variations in the plate scale and the sensitivity of the
detectors. The Cycle 12 program will continue to monitor these effects
and will derive an independent measure of the detector CTE.


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.


Galaxy Evolution in Action : The Detailed Morphology of Post-Starburst

If galaxies evolve morphologically, then some should be in transition
between late and early types. One proposed evolutionary mechanism is a
galaxy-galaxy merger, but evolved merger products are difficult to
find. Fortunately, spectroscopic surveys have now uncovered large
numbers of E+A galaxies, a class of objects whose post-starburst
spectra, current lack of HI gas, and pressure-supported kinematics
suggest that they are the missing panel that connects the "Toomre
sequence" of merging spirals with normal ellipticals and S0s. Our
first HST observations of five of these galaxies are intriguing. We
find a considerable range of tidally disturbed morphologies, an "E+A"
fundamental plane, significant differences among the color gradients
within 1 kpc {~0.8”}, and populations of bright, blue globular
clusters. These initial results are difficult to interpret, however,
because they are drawn from a small sample of galaxies whose very blue
overall colors may have selected a particular evolutionary path of
E+As. Here we propose for ACS imaging of the remaining 15 E+As from
the Las Campanas Redshift Survey to probe the full range of E+A
properties. The proposed observations will allow us to 1} determine
what fraction of the interactions that lead to E+As destroy all
disk-like structures {and therefore necessarily lead to elliptical
formation}, 2} measure the inner color gradients and constrain the
spatial distribution of stars produced as gas sinks to the center
during a merger, and 3} determine whether these interactions produce
globular clusters in the required numbers to account for the increased
specific frequency of clusters in early-type galaxies.

ACS/WFC 9744

HST Imaging of Gravitational Lenses

Gravitational lenses offer unique opportunities to study cosmology,
dark matter, galactic structure, galaxy evolution and quasar host
galaxies. They are also the only sample of galaxies selected based on
their mass rather than their luminosity or surface brightness. While
gravitational lenses can be discovered with ground-based optical and
radio observations, converting them into astrophysical tools requires
HST. We will obtain ACS/WFC V and I images and NICMOS H images of 21
new lenses never observed by HST and NICMOS H images of 16 lenses
never observed by HST in the IR. As in previous cycles, we request
that the data be made public immediately.

ACS/WFC 9891

A snapshot survey of rich stellar clusters in the Large and Small
Magellanic Clouds

Rich stellar clusters are vital to a wide variety of astrophysical
research, from stellar evolution studies to the formation and
evolution of galaxies. In this context, it is important to understand
how rich star clusters form and evolve. The cluster systems in the LMC
and SMC are particularly important in achieving this, because they are
the only systems which contain clusters at all stages of evolution
while being close enough to be studied as fully resolved stellar
populations – although in general this requires the capabilities of
HST. We have recently investigated the structural evolution of LMC and
SMC clusters using archival WFPC2 data, and demonstrated a dramatic
trend in the sizes of these clusters with age. We have shown that this
trend likely represents genuine structural evolution in these
clusters, although it is not clear whether we are observing a
dynamical process or the signature of changing formation conditions.
This result has implications for all astronomical research involving
massive stellar clusters. To develop this work further requires the
extension of our two samples, so that they are statistically
quantifiable. This will allow a number of key questions regarding the
structural evolution trend to be answered. We propose a two-colour
ACS/WFC SNAP survey of rich Magellanic Cloud clusters to achieve this
aim. The unique resolution and sensitivity of ACS/WFC is required for
success, because of the crowded nature of the targets. The SNAP data
will have a large number of additional applications, both to globular
cluster and Magellanic Cloud research.

NIC1/NIC2/NIC3 8792

NICMOS Post-SAA calibration – CR Persistence Part 3

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.

NIC2 9845

NICMOS Confirmation of a Young Planetary-Mass Companion

We have recently discovered a strong candidate for a planetary-mass
{~10 Mjup} companion to a young Sun-like star, based on near-IR
imaging and spectroscopy with the Keck and Subaru adaptive optics {AO}
systems. While the ground-based data strongly suggest that the
candidate has a very low effective temperature, and hence a very low
mass, they are not definitive. We propose to obtain NICMOS
coronagraphy to measure the companion’s 1.9um water-band absorption.
This feature is a distinct signature of very cool objects and is
unobservable from the ground. The combined ground-based and
space-based data set will determine whether the companion has a very
low temperature, and hence if it is the lowest mass companion found to
date by direct imaging.


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/CCD 10018

CCD Dark Monitor-Part 2

Monitor the darks for the STIS CCD.

STIS/CCD 10020

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.


Variable Interstellar Absorption toward HD 219188 — Probing the
Structure of an Interstellar Cloud

Within the last 10 years, strong, narrow Na I absorption has appeared
at v_SUN ~ -38 km s^-1 toward the halo star HD 219188; that absorption
has continued to strengthen, by a factor 2–3, over the past three
years. The line of sight appears to be moving into/through a
relatively cold, quiescent intermediate velocity {IV} cloud, due to
the 13 mas/year proper motion of HD 219188. We propose to monitor the
continuing changes in the IV absorption toward HD 219188 over the next
three years with STIS echelle spectra — making use of the rich
diagnostics provided by the UV lines of various neutral and singly
ionized species to determine abundances/depletions and physical
conditions {temperature, density, ionization} as functions of depth
within the cloud. In addition to providing a unique view of the
detailed structure of an interstellar cloud, these data will yield
constraints on grain scattering parameters {from the variation of
ionization with depth} and on any dependence of depletion on local

WFPC2 10070

WFPC2 CYCLE 12 Supplemental Darks Part 2/3

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


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



                           SCHEDULED     SUCCESSFUL    FAILURE TIMES
GSacq               10                           10
FGS REacq                08                           08
FHST Update             13                           13


Continuing Battery 4 Capacity Test.

FGS 2 K16ACLIM change scheduled during window 155/12:30Z – 18:00Z
while HST is outside SAA 1 contour and FGS 2 is assigned but not
actively guiding (OR 17178 with attached script). TDRSS services
during period 155/12:30Z – 18:00Z have been declared ‘critical’.

SpaceRef staff editor.