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3\07-09 HST Daily Rpt No 3315
Part 1 of 5

 HUBBLE SPACE TELESCOPE
  DAILY REPORT # 3315

PERIOD COVERED: DOYs 66-68

OBSERVATIONS SCHEDULED

ACS 9658

ACS Earth Flats

This program will obtain sequences of flat field images by observing 
the bright Earth. Several UV filters from the interim calibration 
program {9564} require additional exposures to obtain the required 
illumination. A few UV filters from this program will be repeated to 
monitor for changes in the flat fields and to verify the interim 
results. Since no streaks are observed in the UV, the wavelength 
coverage is extended to longer wavelengths in order to explore the 
severity of streaks in the flats from clouds in the FOV. We have added 
exposures for the HRC in the visible filters to verify the results 
derived from the L-flat campaign and to explore the severity of 
streaks. We have also added exposures on WFC using the minimum 
exposure time and using filters which will not saturate the brightest 
WFC pixel by more than 10 times the full well.

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 9673

CCD Daily Monitor

This program consists of basic tests to monitor, the read noise, the 
development of hot pixels and test for any source of noise in ACS CCD 
detectors. This programme will be executed once a day for the entire 
lifetime of ACS

ACS 9480

Cosmic Shear With ACS Pure Parallels

Small distortions in the shapes of background galaxies by foreground 
mass provide a powerful method of 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.

ACS 9293

Massive Black Holes in Early Type Galaxies

Recently, a nearly perfect relation has been recognized between the 
masses of the black holes {for 3x10^6 Msun < M_BH < 3x10^9 Msun} at 
the centers of galaxies and the velocity dispersions of their bulges. 
However, uncertainties over the exact slope of the correlation still 
remain, and it is not known if such a relation extends to black holes 
of lower and higher masses. The discovery of small {r ~ a few hundred 
pc}, well defined, dust and gas disks in the nuclei of some active 
elliptical galaxies opened a new avenue for measuring central mass 
distributions. When ionized gas is present, a small number of high 
spatial resolution {e.g. STIS} spectra are sufficient to characterize 
the disk dynamics and the galaxy's central mass {e.g., M87, M81, NGC 
4374}. We propose to use STIS spectroscopy to measure black hole 
masses, using gas dynamics, in the centers of several brightest 
cluster galaxies {BCGs}, 2 nearby galaxies with low velocity 
dispersions, and a number of elliptical galaxies known to harbor small 
nuclear dust disks. The proposed targets encompass a wide range of 
black hole masses, allowing us to fully examine the M_BH -- sigma 
relationship. We will also obtain H-alpha and continuum images to 
fully characterize the gaseous and dust morphology as well as stellar 
surface profile in the central regions.

ACS 9409

The Evolution of Globular Cluster Systems in Merger Remnants

Mergers seem to have played a major role in determining the shapes and 
dynamics of elliptical galaxies. A few galactic mergers still occur 
and offer valuable clues to past evolutionary processes. Globular 
clusters formed during mergers are crucial probes for age-dating such 
events, and help shed light on the process of cluster formation and 
evolution. With young globulars in ongoing mergers now well studied, 
we propose to make deep ACS observations of intermediate-age globular 
clusters in two bona fide ellipticals: NGC 1316 and 3610. These 
ellipticals have line-strength indices, UBV colors, and fine structure 
indicative of their being 2 -- 4 Gyr old merger remnants. Past 
HST+WFPC2 observations have shown that they also possess significant 
numbers of intermediate-age globulars as part of their bimodal cluster 
populations. We plan to use the new HST+ACS observations to {1} 
measure high-accuracy BVI colors for clusters up to ~ 2 -- 3 mag 
fainter than ever before, {2} use these colors to separate first- and 
second-generation clusters, and {3} determine the luminosity functions 
of the two kinds of clusters to 3 -- 4 mag past the peak for old
globulars. Deep dithered BVI images form a crucial part of our 
observing strategy. This program should permit---for the first 
time---to directly detect the predicted evolution of the cluster 
luminosity function from a power law for young clusters to the 
Gaussian distribution typical of old globulars.

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