Status Report

NASA Hubble Space Telescope Status Report # 3723

By SpaceRef Editor
October 26, 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/HRC 10198

Probing the Dynamics of the Galactic Bar through the Kinematics of
Microlensed Stars

The observed optical depths to microlensing of stars in the Galactic
bulge are difficult to reconcile with our present understanding of
Galactic dynamics. The main source of uncertainty in those comparisons
is now shifting from microlensing measurements to the dynamical models
of the Galactic bar. We propose to constrain the Galactic bar models
with proper motion observations of Bulge stars that underwent
microlensing by determining both the kinematic identity of the
microlensed sources and the importance of streaming motions. The
lensed stars are typically farther than randomly selected stars.
Therefore, our proper motion determinations for 36 targeted MACHO
events will provide valuable constraints on the dynamics of bulge
stars as a function of distance. The first epoch data for our proposed
events is already available in the HST archive so the project can be
completed within a single HST cycle. The exceptional spatial
resolution of HST is essential for completion of the project.
Constraints on the total mass in the bulge will ultimately lead to the
determination of the amount of dark matter in inner Galaxy.

ACS/HRC 10332

Starburst Galaxies and Their Population of Super Star Clusters

Starbursts are ideally suited to study the evolution of high mass
stars, the physics of star formation, and the chemical enrichment of
the intergalactic medium {IGM}. Starbursts efficiently form Super Star
Clusters {SSC} which may be young protoglobular clusters. High
resolution imaging will address two important outstanding issues: 1}
how long starbursts last and 2} whether SSCs are indeed young globular
clusters. The duration of starbursts is important because: {1} it
determines how efficiently a starburst can heat and enrich the IGM;
{2} the duration combined with estimates of the fraction of galaxies
which host starbursts yields the total number of starbursts a galaxy
can suffer. Finally, since local starbursts are analogs to high-z
galaxies, the results have implications on the initial formation
timescale of galaxies. Starburst duration will be determined from HRC
imaging of two face-on starburst galaxies rich in SSCs. The UV to
optical colors of the SSCs, which represent single burst chronometers,
will yield their reddening and ages. The range of ages gives the
starburst duration. The nature of SSCs will be investigated by imaging
four of the nearest starbursts in three bands. By comparing the sizes
of their SSCs at different wavelengths we will address the issue of
whether SSCs suffer from early mass segregation. Without some mass
segregation the velocity dispersions of SSCs suggest that they are
deficient in low mass stars, and hence may not represent true
proto-globular clusters.

ACS/HRC 10390

Serendipitous detection of a debris disk near the Sun

We report the unexpected detection of the Fomalhaut debris disk in
scattered light during one orbit of observation for our Cycle 12
program GO9862. This is a major discovery because Fomalhaut is now the
closest {7.7 pc} and oldest {~200 Myr} debris disk detected in
reflected light. We would like to request Director’s Discretionary
Time to further study the Fomalhaut disk. The goals are to image the
disk around its entire perimeter, increase the signal-to-noise of the
detection, and to obtain data at a second wavelength. We will perform
a high-resolution study of radial and azimuthal disk asymmetries that
are thought to arise from perturbations by planet-mass companions, and
we will constrain the physical properties of grain material by
obtaining the color of the disk. Because our original Cycle 12 program
was designed to study point sources in the field, and the ACS/HRC
coronagraph is a limited lifetime resource, it is necessary to acquire
these additional data via Director’s Discretionary Time during Cycle
13. The observational challenge of high contrast cannot be met by
other observatories, and these data will complement new Spitzer
results on the Fomalhaut disk at mid and far-infrared wavelengths.


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.


The HST survey of the Orion Nebula Cluster

We propose a Treasury Program of 104 HST orbits to perform the
definitive study of the Orion Nebula Cluster, the Rosetta stone of
star formation. We will cover with unprecedented sensitivity {23-25
mag}, dynamic range {~12 mag}, spatial resolution {50mas}, and
simultaneous spectral coverage {5 bands} a ~450 square arcmin field
centered on the Trapezium stars. This represents a tremendous gain
over the shallow WFC1 study made in 1991 with the aberrated HST on an
area ~15 times smaller. We maximize the HST observing efficiency using
ACS/WFC and WFPC2 in parallel with two opposite roll angles, to cover
the same total field. We will assemble the richest, most accurate and
unbiased HR diagram for pre-main-sequence objects ever made. Combined
with the optical spectroscopy already available for ~1000 sources and
new deep near-IR imaging and spectroscopy {that we propose as Joint
HST-NOAO observations}, we will be able to attack and possibly solve
the most compelling questions on stellar evolution: the calibration of
pre-main-sequence evolutionary tracks, mass segration and the
variation of the initial mass function in different environments, the
evolution of mass accretion rates vs. age and environment, disk
dissipation in environments dominated by hard vs. soft-UV radiation,
stellar multiplicity vs. disk fraction. In addition, we expect to
discover and classify an unknown, but substantial, population of
pre-Main Sequence binaries, low mass stars and brown dwarfs down to
~10 MJup. This is also the best possible way to discover dark
silhouette disks in the outskirts of the Orion Nebula and study their
evolutionary status through multicolor imaging. This program is timely
and extremely well leveraged to other programs targeting Orion: the
ACS H-alpha survey of the Orion Nebula, the recently completed 850ks
ultradeep Chandra survey, the large GTO programs to be performed with
SIRTF, plus the availability of 2MASS and various deep JHK surveys of
the core recently done with 8m class telescopes.

FGS 10387

Monitoring FGS1r’s Interferometric Response as a Function of Spectral

This proposal obtains reference point source Transfer Functions
{S-Curves} for FGS1r through the F583W filter and the F5ND attenuator
at the center position of the FGS1r FOV for a variety of stars of
different spectral types. These Transfer Functions are needed to
support the analysis of GO science data for the study of close and
wide binary star systems and for determining the angular size and
shape of extended sources. This proposal observes stars that have been
observed in previous cycles to monitor the long term evolution of the
FGS1r S-curves. This proposal also {1} monitors the FGS1r Lateral
Color response {using stars Latcol-A and Latcol-B}, {2} calibrates the
“Pos/Trans” bias of a star’s position as determined from Transfer mode
and Position mode observations, and {3} calibrates the shift of a
star’s centroid when observed with F5ND relative to that when observed
with F583W.

FGS 9972

Calibrating the Mass-Luminosity Relation at the End of the Main

We propose to use HST-FGS1R to calibrate the mass-luminosity relation
{MLR} for stars less massive than 0.2 Msun, with special emphasis on
objects near the stellar/brown dwarf border. Our goals are to
determine M_V values to 0.05 magnitude, masses to 5 than double the
number of objects with masses determined to be less than 0.20 Msun.
This program uses the combination of HST-FGS3/FGS1R at optical
wavelengths and ground-based infrared interferometry to examine
nearby, subarcsecond binary systems. The high precision measurements
with HST-FGS3/FGS1R {to 1 mas in the separations} for these faint
targets {V = 10–15} simply cannot be equaled by any ground based
technique. As a result of these measurements, we are deriving high
quality luminosities and masses for the components in the observed
systems, and characterizing their spectral energy distributions from
0.5 to 2.2 Mum. Several of the objects included have M < 0.1 Msun, placing them at the very end of the stellar main sequence. Three of the targets are brown dwarf candidates, including the current low mass record holder, GJ 1245C, with a mass of 0.062 +/- 0.004 Msun. The payoff of this proposal is high because all 10 of the systems selected have already been resolved with HST- FGS3/FGS1R during Cycles 5--10 and contain most of the reddest objects for which masses can be determined.

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.


Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be

HSTAR 9570: FHST 3 Map failed to lock onto any stars @ 298/08:54Z.



                          SCHEDULED     SUCCESSFUL    FAILURE TIMES
FGS Gsacq               13                       13
FGS Reacq                02                       02
FHST Update             19                       19


SpaceRef staff editor.