Status Report

NASA Hubble Space Telescope Daily Report #3862

By SpaceRef Editor
May 19, 2005
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HUBBLE SPACE TELESCOPE – Continuing to collect World Class Science

DAILY REPORT        #3862



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 10398

Transcending Voyager: A Deeper Look at Neptune’s Ring-Moon System

We will use the High Resolution Channel {HRC} of ACS to study the
inner rings, arcs and moons of Neptune with a sensitivity that exceeds
that achieved by Voyager 2 during its 1989 flyby. Our study will
reveal any moons down to V magnitude 25.5, to address a peculiar
truncation in the size distribution of inner moons and to look for the
“shepherds” and source bodies for Neptune’s dusty rings. {For
comparison, Neptune’s smallest known moon is Naiad, at magnitude
23.9}. Recent ground-based studies show that the mysterious arcs in
the Adams Ring continue to shift and change, and may be fading away
entirely. We will obtain the visual-band data uniquely necessary to
determine whether the arcs are fading. Long-term monitoring of the
arcs at high resolution and sensitivity will reveal their gradual
changes more clearly and enable us to assess the role of Galatea,
whose resonances are widely believed to confine the arcs.

FGS 10106

An Astrometric Calibration of the Cepheid Period-Luminosity Relation

We propose to measure the parallaxes of 10 Galactic Cepheid variables.
When these parallaxes {with 1-sigma precisions of 10% or better} are
added to our recent HST FGS parallax determination of delta Cep
{Benedict et al 2002}, we anticipate determining the Period-Luminosity
relation zero point with a 0.03 mag precision. In addition to
permitting the test of assumptions that enter into other Cepheid
distance determination techniques, this calibration will reintroduce
Galactic Cepheids as a fundamental step in the extragalactic distance
scale ladder. A Period-Luminosity relation derived from solar
metallicity Cepheids can be applied directly to extragalactic solar
metallicity Cepheids, removing the need to bridge with the Large
Magellanic Cloud and its associated metallicity complications.

NIC3/ACS/WFC 10327

ACS Imaging of a High-Redshift Cluster of Galaxies

This programme uses ACS observations of the high-redshift radio galaxy
MRC1138- 262 {z=2.16} to investigate massive galaxy and cluster
formation in the early Universe. This field is unique in that it is
known to contain overdensities in both line-emitting {both Lyman-alpha
and H-alpha} and continuum {4000A break} objects. Utilizing the
excellent angular-resolution and field-coverage of HST/ACS we can
obtain the colors and morphologies for a substantial fraction of these
protocluster galaxies. These morphologies and colors will be compared
to studies of field galaxies at similar redshifts {e.g., from GOODS}.
In addition, very deep images of the radio galaxy itself, the presumed
central dominant galaxy of this cluster, will allow us to study in
detail the process of formation for the most massive known galaxies.
The properties of continuum and Ly-alpha clumps within the radio
galaxy will be compared in relation to the radio structures.

NIC3/WFPC2 10277

Ages and Metallicities of the Intergalactic Globular Cluster
Population in Abell 1185 We will obtain deep NICMOS observations of a
recently discovered population of intergalactic globular clusters in
the nearby galaxy cluster Abell 1185. These H band observations in
conjunction with deep V and I images that we obtained with ACS in
Cycle 11 will allow us to measure the ages and metallicities of these
objects from their optical and near-infrared colors, which will
provide important insights to their origin. We will also obtain
parallel observations with both ACS and WFPC2. ACS parallel
observations will be used to obtain deep images to search for
intergalactic globular clusters in a different region of Abell 1185.
WFPC2 parallel observations will be used to obtain images of
interacting galaxy pair Arp 105, to search for globular clusters
currently being ejected into intergalactic space as a result of this


NICMOS Post-SAA calibration – CR Persistence Part 1.

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.

WFPC2 10360


This calibration proposal is the Cycle 13 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.


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

HSTARS: (None)



                           SCHEDULED     SUCCESSFUL    FAILURE TIMES 
 FGS Gsacq                 9                        9 
 FGS Reacq                 6                         6 
 FHST Update             14                       14 


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