Status Report

NASA Hubble Space Telescope Daily Report # 3715

By SpaceRef Editor
October 14, 2004
Filed under , ,

HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science




ACS/HRC 10185

When does Bipolarity Impose itself on the Extreme Mass Outflows from
AGB Stars? An ACS SNAPshot Survey

Essentially all well-characterized preplanetary nebulae {PPNe} —
objects in transition between the AGB and planetary nebula
evolutionary phases – are bipolar, whereas the mass-loss envelopes of
AGB stars are strikingly spherical. In order to understand the
processes leading to bipolar mass-ejection, we need to know at what
stage of stellar evolution does bipolarity in the mass-loss first
manifest itself? Our previous SNAPshot surveys of a PPNe sample {with
ACS & NICMOS} show that roughly half our targets observed are
resolved, with well-defined bipolar or multipolar morphologies.
Spectroscopic surveys of our sample confirm that these objects have
not yet evolved into planetary nebulae. Thus, the transformation from
spherical to aspherical geometries has already fully developed by the
time these dying stars have become preplanetary nebulae. From this
new and surprising result, we hypothesize that the transformation to
bipolarity begins during the very late AGB phase, and happens very
quickly, just before, or as the stars are evolving off the AGB. We
propose to test this hypothesis quantitatively, through a SNAPshot
imaging survey of very evolved AGB stars which we believe are nascent
preplanetary nebulae; with our target list being drawn from published
lists of AGB stars with detected heavy mass-loss {from millimeter-wave
observations}. This survey is crucial for determining how and when the
bipolar geometry asserts itself. Supporting kinematic observations
using long-slit optical spectroscopy {with the Keck}, millimeter and
radio interferometric observations {with OVRO, VLA & VLBA} are being
undertaken. The results from this survey {together with our previous
work} will allow us to draw general conclusions about the onset of
bipolar mass-ejection during late stellar evolution, and will provide
crucial input for theories of post-AGB stellar evolution. Our survey
will produce an archival legacy of long-standing value for future
studies of dying stars.


ACS CCDs daily monitor- cycle 13 – part 1

This program consists of a set of basic tests to monitor, the read
noise, the development of hot pixels and test for any source of noise
in ACS CCD detectors. The files, biases and dark will be used to
create reference files for science calibration. This programme will be
for the entire lifetime of ACS.

ACS/WFC 10118

Imaging the Chemical Distribution in Type Ia SN Ejecta

We know Type Ia supernovae are thermonuclear explosions of CO white
dwarfs, but we don’t know the specifics of how the nuclear burning
process proceeds from the core outward once it starts. The
thermonuclear instability is thought to start off as a subsonic,
turbulent deflagration or burning wave but then, at some point, may
transition into a blast or detonation wave. In such "delayed
detonation" models, differences between normal and subluminous Type Ia
SNe reflect differences in the amount of burning that has occurred in
the pre-detonation phase. More burning helps to pre-expand the WD
before passage of the detonation wave, which then results in different
final element abundances and internal Fe-rich ejecta structure.
Directly imaging the 2-D chemical distribution of ejecta from a Type
Ia SN is actually possible in the case of the subluminous Type Ia SN
1885, which occurred on the near-side of M31’s central bulge. This 119
year old remnant is visible — from its core to its outer edge — via
strong optical/UV Ca and Fe line absorptions. Remarkably, the SNR
appears to still be in a nearly free expansion phase, meaning that the
elemental stratification seen present today accurately reflects SN Ia
explosive nucleosynthesis physics. We propose to obtain ACS WFC/HRC
images of SN 1885 in order to take advantage of this extraordinary
situation: Having a young, nearby Type Ia SN remnant visible in
silhouette against a galaxy-size light table. These unique
observations will reveal a SN Ia’s Ca and Fe ejecta distribution,
density structure, sphericity, and ionization state as a function of
expansion velocity, thereby confronting various SN Ia models with
detailed ejecta stratification and expansion velocity maps.


The COSMOS 2-Degree ACS Survey

We will undertake a 2 square degree imaging survey {Cosmic Evolution
Survey — COSMOS} with ACS in the I {F814W} band of the VIMOS
equatorial field. This wide field survey is essential to understand
the interplay between Large Scale Structure {LSS} evolution and the
formation of galaxies, dark matter and AGNs and is the one region of
parameter space completely unexplored at present by HST. The
equatorial field was selected for its accessibility to all
ground-based telescopes and low IR background and because it will
eventually contain ~100, 000 galaxy spectra from the VLT-VIMOS
instrument. The imaging will detect over 2 million objects with I> 27
mag {AB, 10 sigma}, over 35, 000 Lyman Break Galaxies {LBGs} and
extremely red galaxies out to z ~ 5. COSMOS is the only HST project
specifically designed to probe the formation and evolution of
structures ranging from galaxies up to Coma-size clusters in the epoch
of peak galaxy, AGN, star and cluster formation {z ~0.5 to 3}. The
size of the largest structures necessitate the 2 degree field. Our
team is committed to the assembly of several public ancillary datasets
including the optical spectra, deep XMM and VLA imaging, ground-based
optical/IR imaging, UV imaging from GALEX and IR data from SIRTF.
Combining the full-spectrum multiwavelength imaging and spectroscopic
coverage with ACS sub-kpc resolution, COSMOS will be Hubble’s ultimate
legacy for understanding the evolution of both the visible and dark

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.

NIC1/NIC2/NIC3 9723

Deep NICMOS imaging

We have obtained ultra-deep Js, H, Ks imaging of the Hubble Deep Field
South WFPC2 field with the VLT, in order to study high redshift
galaxies. The Ks-band data are the deepest obtained to date in any
field. We find that the population of Ks selected galaxies at z=2-4 in
HDF-South differs in two important aspects from previous studies in
HDF-North. First, we find several galaxies which are large and
apparently regular in the rest-frame optical, with more complex rest-
frame UV morphologies. These objects resemble large disk galaxies in
the local Universe. Second, we have identified a population of
galaxies with red J-K colors that are extremely faint in the
rest-frame UV. The galaxies have ages of 0.5-2 Gyr and are highly
clustered, and may be progenitors of nearby bulges and early-type
galaxies. We propose to obtain a deep mosaic with the NICMOS/NIC3
camera in the H band, covering the WFPC2 field. The increased depth
and spatial resolution of the NICMOS mosaic would allow us to
determine the restframe optical morphologies of a large sample of high
redshift galaxies, in order to study the relative distributions of
young and old stars, to decompose the galaxies in bulges and disks, to
measure scale lengths, and to model the stellar populations of the
sub-components. The lack of large U- dropouts and red galaxies in
HDF-North, and the need for larger samples call for the proposed
imaging of HDF-South. We waive all proprietary rights.

NIC2 10176

Coronagraphic Survey for Giant Planets Around Nearby Young Stars

A systematic imaging search for extra-solar Jovian planets is now
possible thanks to recent progress in identifying "young stars near
Earth". For most of the proposed young {<~ 30 Myrs} and nearby {<~ 60
pc} targets, we can detect a few Jupiter-mass planets as close as a
few tens of AUs from the primary stars. This represents the first time
that potential analogs of our solar system – that is planetary systems
with giant planets having semi-major axes comparable to those of the
four giant planets of the Solar System – come within the grasp of
existing instrumentation. Our proposed targets have not been observed
for planets with the Hubble Space Telescope previously. Considering
the very successful earlier NICMOS observations of low mass brown
dwarfs and planetary disks among members of the TW Hydrae Association,
a fair fraction of our targets should also turn out to posses low mass
brown dwarfs, giant planets, or dusty planetary disks because our
targets are similar to {or even better than} the TW Hydrae stars in
terms of youth and proximity to Earth. Should HST time be awarded and
planetary mass candidates be found, proper motion follow-up of
candidate planets will be done with ground-based AOs.

NIC2 10177

Solar Systems In Formation: A NICMOS Coronagraphic Survey of
Protoplanetary and Debris Disks

Until recently, despite decades of concerted effort applied to
understanding the formation processes that gave birth to our solar
system, the detailed morphology of circumstellar material that must
eventually form planets has been virtually impossible to discern. The
advent of high contrast, coronagraphic imaging as implemented with the
instruments aboard HST has dramatically enhanced our understanding of
natal planetary system formation. Even so, only a handful of evolved
disks {~ 1 Myr and older} have been imaged and spatially resolved in
light scattered from their constituent grains. To elucidate the
physical processes and properties in potentially planet-forming
circumstellar disks, and to understand the nature and evolution of
their grains, a larger spatially resolved and photometrically reliable
sample of such systems must be observed. Thus, we propose a highly
sensitive circumstellar disk imaging survey of a well-defined and
carefully selected sample of YSOs {1-10 Myr T Tau and HAeBe stars} and
{> app 10 Myr} main sequence stars, to probe the posited epoch of
planetary system formation, and to provide this critically needed
imagery. Our resolved images will shed light on the spatial
distributions of the dust in these thermally emissive disks. In
combination with their long wavelength SEDs the physical properties of
the grains will be discerned, or constrained by our photometrically
accurate surface brightness sensitivity limits for faint disks which
elude detection. Our sample builds on the success of the exploratory
GTO 7233 program, using two-roll per orbit PSF-subtracted NICMOS
coronagraphy to provide the highest detection sensitivity to the
smallest disks around bright stars which can be imaged with HST. Our
sample will discriminate between proposed evolutionary scenarios while
providing a legacy of cataloged morphologies for interpreting mid- and
far-IR SEDs that the recently launched Spitzer Space Telescope will

NIC3 10337

The COSMOS 2-Degree ACS Survey NICMOS Parallels

The COSMOS 2-Degree ACS Survey NICMOS Parallels. This program is a
companion to program 10092.


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



                           SCHEDULED     SUCCESSFUL    FAILURE TIMES
FGS Gsacq                13                       13
FGS Reacq                 05                       05
FHST Update              14                       14


Solar eclipse event due to Moon’s occultation of the Sun 288/04:00:47Z
– 04:26:31Z. The event occurred in the middle of orbit day
288/03:24:14Z – 04:26:31Z, with the percentage of darkness below 3%
compared to the orbit night period. Based on previous eclipse event
where the darkness percentage was as much as 17.2%, no action was
necessary during this eclipse event.

SpaceRef staff editor.