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3\13 HST Daily Rpt No 3319
Part 2 of 3

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 9480

Cosmic Shear With ACS Pure Parallels

directly measuring the amount and distribution of dark matter. Several 
groups have recently detected this weak lensing by large-scale 
structure, also called cosmic shear. The high resolution and 
sensitivity of HST/ACS provide a unique opportunity to measure cosmic 
shear accurately on small scales. Using 260 parallel orbits in Sloan 
textiti {F775W} we will measure for the first time:  
beginlistosetlength sep0cm setlengthemsep0cm setlength opsep0cm em the 
cosmic shear variance on scales <0.7 arcmin, em the skewness of the 
shear distribution, and em the magnification effect. endlist Our 
measurements will determine the amplitude of the mass power spectrum 
sigma_8Omega_m^0.5, with signal-to-noise {s/n} ~ 20, and the mass 
density Omega_m with s/n=4. They will be done at small angular scales 
where non-linear effects dominate the power spectrum, providing a test 
of the gravitational instability paradigm for structure formation.
Measurements on these scales are not possible from the ground, because 
of the systematic effects induced by PSF smearing from seeing. Having 
many independent lines of sight reduces the uncertainty due to cosmic 
variance, making parallel observations ideal.

NICMOS 9484

The NICMOS Parallel Observing Program

We propose to manage the default set of pure parallels with NICMOS. 
Our experience with both our GO NICMOS parallel program and the public 
parallel NICMOS programs in cycle 7 prepared us to make optimal use of 
the parallel opportunities. The NICMOS G141 grism remains the most 
powerful survey tool for HAlpha emission-line galaxies at 
cosmologically interesting redshifts. It is particularly well suited 
to addressing two key uncertainties regarding the global history of 
star formation: the peak rate of star formation in the relatively 
unexplored but critical 1<= z <= 2 epoch, and the amount of star 
formation missing from UV continuum-based estimates due to high 
extinction. Our proposed deep G141 exposures will increase the sample 
of known HAlpha emission- line objects at z ~ 1.3 by roughly an order 
of magnitude. We will also obtain a mix of F110W and F160W images 
along random sight-lines to examine the space density and morphologies 
of the reddest galaxies. The nature of the extremely red galaxies 
remains unclear and our program of imaging and grism spectroscopy 
provides unique information regarding both the incidence of obscured 
star bursts and the build up of stellar mass at intermediate 
redshifts. In addition to carrying out the parallel program we will 
populate a public database with calibrated spectra and images, and 
provide limited ground- based optical and near-IR data for the deepest 
parallel fields.

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 9589

WFPC2 Decontaminations and Associated Observations Pt. 1/3

This proposal is for the monthly WFPC2 decons. Also included are 
instrument monitors tied to decons: photometric stability check, focus 
monitor, pre- and post-decon internals {bias, intflats, kspots, & 
darks}, UV throughput check, VISFLAT sweep, and internal UV flat 
check.

WFPC2 9594

WFPC2 CYCLE 11 SUPPLEMENTAL DARKS pt2/3

This dark calibration program obtains 3 dark frames every day to 
provide data for monitoring and characterizing the evolution of hot 
pixels

CAL/WF2 9597

Intflat Sweep, Visflat Sweep, and Filter Anomaly Check

No abstract available.

WFPC2 9598

Earth Flats

This proposal monitors flatfield stability. This proposal obtains 
sequences of Earth streak flats to 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.

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