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8 May 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT # 3358

PERIOD COVERED: DOY 127

Part 2 of 3

ACS 9462

Systemic and Internal Proper Motions of the Magellanic Clouds from
Astrometry with ACS

We request first epoch observations with ACS of Magellanic Cloud fields 
centered on background quasars. Second epoch observations will be
requested ~ 5 years later to allow the measurement of the systemic
and internal proper motions of the Clouds with error <~0.05 mas/year.
These motions are of fundamental importance. The systemic motions of
the LMC and SMC probe the gravitational potential of the dark halo.
The internal proper motion due to rotation can be exploited to yield
a rotational parallax distance to the LMC; the first time that this
will be done for any galaxy. This is particularly important for the
LMC because of its crucial role in the extragalctic distance ladder.
Previous measurements of the proper motion of the LMC yield a
systemic component ranging from 1.4 mas/year to 3.4 mas/year
{differing by several times the quoted errors}, with no useful
determination of the internal motions. The main problem with
measurements of the proper motion of the LMC has been the lack of a
sample of background quasars to use as reference frame. We have
recently been able to identify a sample of 54 quasars behind the
Magellanic Clouds from their variability characteristics in the MACHO
database. With this sample and the advent of ACS an accurate proper
motion measurement has become possible for the very first time.

ACS 9463

Are OH/IR stars the youngest post-AGB stars? An ACS SNAPshot imaging
survey

Essentially all well-characterized preplanetary nebulae {PPNs}--
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? We have recently hypothesized that most OH/IR stars
{evolved mass- losing stars with OH maser emission} are very young
PPNe. We propose an ACS/SNAPshot imaging survey of a large,
morphologically unbiased sample of these objects, selected using
their IRAS 12-to-25micron colors. Our ground-based imaging study of
OH/IR stars has revealed a few compact bipolar objects, supporting
our hypothesis. However since most objects remain unresolved, HST
observations are needed to determine how and when the bipolar
geometry asserts itself. Our complementary program of interferometric
mapping of the OH maser emission in our sources is yielding kinematic
information with spatial resolution comparable to that in the HST
images. The HST/radio data will provide crucial input for theories of
post-AGB stellar evolution. In addition, these data will also
indicate whether the multiple concentric rings, ``searchlight
beams'', and truncated equatorial disks recently discovered with HST
in a few PPNs, are common or rare phenomena. 

ACS 9468

ACS Grism Parallel Survey of Emission- line Galaxies at Redshift
z pl 7

sight over the redshift interval 0 < zpl 7. We request ACS parallel
observations of duration more than one orbit at high galactic
latitude to identify ~ 300 HAlpha emission-line galaxies at
0.2pl z pl 0.5, ~ 720 O IILambda3727 emission-line galaxies at
0.3pl zpl 1.68, and pg 1000 Ly-alpha emission-line galaxies at
3pl zpl 7 with total emission line flux fpg 2* 10^-17 ergs
s^-1 cm^-2 over 578 arcmin^2. We will obtain direct images with the
F814W and F606W filters and dispersed images with the WFC/G800L grism
at each position. The direct images will serve to provide a zeroth
order model both for wavelength calibration of the extracted 1D
spectra and for determining extraction apertures of the corresponding
dispersed images. The primary scientific objectives are as follows:
{1} We will establish a uniform sample of HAlpha and O II
emission-line galaxies at z<1.7 in order to obtain accurate
measurements of co-moving star formation rate density versus redshift
over this redshift range. {2} We will study the spatial and
statistical distribution of star formation rate intensity in
individual galaxies using the spatially resolved emission-line
morphology in the grism images. And {3} we will study high-redshift
universe using Ly-alpha emitting galaxies identified at z pl 7 in
the survey. The data will be available to the community immediately
as they are obtained.

NICMOS 9485

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. 

WFPC2 9594

WFPC2 CYCLE 11 SUPPLEMENTAL DARKS pt2/3

characterizing the evolution of hot pixels

WFPC2 9598

Earth Flats

construct high quality flat fields for the WFPC2 filter set. These
flat fields will allow mapping of the OTA illumination pattern and
will be used in conjunction with previous internal and external flats
to generate new pipeline superflats. These Earth flats will
complement the Earth flat data obtained during cycles 4-10.

STIS 9606

CCD Dark Monitor-Part 2

Monitor the darks for the STIS CCD.

 - Continued -

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