Status Report

NASA Hubble Space Telescope Daily Report # 3681

By SpaceRef Editor
August 25, 2004
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HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science





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.

ACS/WFC 10158

ACS Observations of the Gravitational Lens B1608+656: Characterizing
the Einstein Ring

We request time to obtain ACS deep images of the B1608+656
gravitational lens system to fully characterize its enclosing Einstein
ring with high signal-to-noise ratio {SNR}. These data will allow us
to determine the gravitational potential of the lens, locally, to
several percent accuracy and, combined with the three independent time
delays, measure H_0 to much better than 10% precision. For this goal,
we have developed powerful new lens modeling codes that make use of
the full brightness distribution of the Einstein ring in lens systems.
The B1608+656 system is ideal for our new code. It has precisely
measured time delays, a well-determined stellar velocity dispersion,
and an Einstein ring that is not dominated by the lensed nuclear
emission of the background source. When combined with high-SNR images
of Einstein rings, the new modeling codes provide qualitatively
different and much improved analysis of the ring emission than was
previously possible. The proposed ACS observations will reach the SNR
at which the new modeling code can be fully exploited {SNR=5 per
pixel}. Our simulations show that these new data will allow us to
reduce the total uncertainties in H_0 derived from the system by at
least a factor of two, to the 5-7% level for this system.

ACS/WFC 10178

Imaging Polarimetry of Young Stellar Objects with ACS and NICMOS: A
study in dust grain evolution

The formation of planetary systems is intimately linked to the dust
population in circumstellar disks, thus understanding dust grain
evolution is essential to advancing our understanding of how planets
form. By combining {1} the high resolution polarimetric capabilities
of ACS and NICMOS, {2} powerful 3-D radiative transfer codes, and {3}
observations of objects known to span the earliest stellar
evolutionary phases, we will gain crucial insight into the initial
phases of dust grain growth: evolution away from an ISM distribution.
Fractional polarization is a strong function of wavelength, therefore
by comparing polarimetric images in the optical and infrared, we can
sensitively constrain not only the geometry and optical depth of the
scattering medium, but also the grain size distribution. By observing
objects representative of the earliest evolutionary sequence of YSOs,
we will be able to investigate how the dust population evolves in size
and distribution during the crucial transition from a disk+envelope
system to a disk+star system. The proposed study will help to
establish the fundamental time scales for the initial depletion of
ISM-like grains: the first step in understanding the transformation
from small submicron sized dust grains, to large millimeter sized
grains, and untimely to planetary bodies.

FGS 10110

Parallaxes of Extreme Halo Subgiants: Calibrating Globular Cluster
Distances and the Ages of the Oldest Stars

The ages of the oldest stars are a key constraint on the evolution of
our Galaxy, the history of star formation, and cosmological models.
These ages are usually determined from globular clusters. However, it
is alternatively possible to determine ages of extreme Population II
subgiants in the solar neighborhood based on trigonometric parallaxes,
without any recourse to clusters. This approach completely avoids the
vexing issues of cluster distances, reddenings, and chemical
compositions. There are 3 known nearby, extremely metal-deficient Pop
II subgiants with Hipparcos parallax errors of 6-11% which are
available for such age determinations. At present, based on the latest
isochrones, the derived ages of these stars {HD 84937, HD 132475, and
HD 140283} are all close to 14 Gyr, uncomfortably close to or higher
than current estimates of the age of the universe. However, the errors
in the Hipparcos parallaxes imply uncertainties of at least 2 Gyr in
the ages of the 3 stars. We propose to measure parallaxes of these
three Pop II subgiants using HST’s Fine Guidance Sensor 1R. We expect
to reduce the Hipparcos parallax error bars by factors of 5-6,
providing the most stringent test yet of current theoretical stellar
models of Pop II stars and pushing the age uncertainties to below 0.5
Gyr. These data will also provide a major new constraint on the
distance scale of globular clusters, with wide implications for
stellar evolution and the calibration of Pop II standard candles.

NIC1/NIC2/NIC3 8793

NICMOS Post-SAA calibration – CR Persistence Part 4

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 9752

A Search for the Exciting Sources in OMC-1 through NICMOS Polarization

Orion contains the site of the nearest region of massive star
formation to the Sun; only here can this pivotal process in galactic
evolution be studied at the highest resolution. There are 10^5 solar
luminosities of radiation emitted from the Orion Molecular Cloud
{OMC-1}, possibly from a young massive star or protostar, or possibly
from several, less luminous sources. Either way, the powering
source{s} in the closest site of massive star formation has still not
yet been identified. Here we propose to apply a new tool to determine
which, of several prospective sources, might prove to be the heart of
OMC-1. The sources cannot be seen directly because they lie in, or
behind, a warm, dense molecular cloud. However, their presence can be
inferred in polarized light, through the manner in which light is
scattered off neighboring clouds. Heretofore, the spatial resolution
has not been adequate to identify the locations of individual stars.
We propose to use the NICMOS polarizers combined with the high spatial
resolution of HST to achieve this, in spite of the high density of
candidate objects in the core of Orion. The demands of accurately
measuring the polarization vectors of small, diffuse objects relative
to the surrounding background from dust-scattered light requires the
high Strehl ratio and stable point-spread function only achievable
from space.

NIC2 9867

How Do Brown Dwarfs Form?

With NICMOS/NIC2 imaging of five brown dwarfs and one low mass star
that we have identified in a young cluster in OMC2/3, we plan to
assess the similarities between brown dwarf formation and low mass
star formation by searching for the presence of shocked H2 line
emission from jets/outflows, close binary companions, and/or
reflection nebulosity from protostellar envelopes and outflow
cavities. The detection of these phenomena would be evidence that
brown dwarfs result from the continuation of the star formation
process to masses below the hydrogen burning limit, and not through
the dynamical ejection of stellar embryos as has been recently
proposed. This proposal is complementary to our SIRTF GTO program
designed to search for circumstellar disks by measuring the spectral
energy distribution of these sources out to 8 microns. This task
requires not only high spatial resolution, but also a stable,
unchanging PSF such as HST provides.

WFPC2 10071

WFPC2 CYCLE 12 Supplemental Darks Part 3/3

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

HSTAR 9522: GS Acquisition (1,2,1) @ 237/17:35:52Z failed to RGA
control due to SRLE on FGS 1. Two FHST FM Updates scheduled prior to
the GS acquisition both occurred during LOS, however they both
succeeded and the second on had a very low vehicle error observed at
AOS. The T2 Slew scheduled @ 237/17:19:57Z had a slew angle of 37.427
degrees. The Search Radius for the GS Acquisition was 55 arcsec.
FHST Map @ 237/17:43:26Z showed errors of 1.840, -2.830, and 11.177
arcsec. Under investigation.



1260-0 Table Dump @ 237/16:00z

1262-0 Lower STIS Bulkhead 6 Temperature 00BBH6T @ 238/01:53z

                            SCHEDULED     SUCCESSFUL    FAILURE TIMES
FGS GSacq                08                        07             See Hstar 
# 9522
FGS REacq                07                        07
FHST Update              11                        11


Battery 3 Capacity Test continues. Continuous ESTR Engineering
Coverage during Battery 3 Capacity Test.

SpaceRef staff editor.