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07 April 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT       # 3336

PERIOD COVERED: DOY 97

Part 2 of 3

ACS 9454

The Nature of the UV Continuum in LINERs: A Variability Test

LINERs may be the most common AGNs, and the signposts of accretion
onto the massive black holes present in most galaxies. However, the
LINER spectrum is the result of UV excitation, and, in at least some
LINERs, a nuclear cluster of hot stars, rather than an AGN, dominates
the energetics in the UV. Thus, it is still unknown if the UV
continuum, or the optical emission lines it excites, have anything to
do with an AGN. The demographics and accretion physics of
low-luminosity AGNs hinge on this question. We propose to search for
variability in a sample of 17 LINERs with compact UV nuclei.
Variability can reveal an AGN component in the UV continuum, even
when its light is not dominant. We will test systematically the
handful of non-definitive reports of UV variability, and potentially
quantify the AGN contribution to the UV emission. Variability in all
or most objects will be strong evidence that LINERs mark dormant AGNs
in most galaxies. Alternatively, a general null detection of
variability will suggest that, even in LINERs with additional AGN
signatures, the UV continuum is stellar in origin. Contemporaneous
monitoring with the VLA/VLBA of 11 objects which have radio cores
{five of which we already know are radio-variable} will reveal the
relations between UV and radio variations. The UV-variable objects
will be targeted for future, better-sampled, monitoring. 

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/WFPC2 9488

Cosmic Shear - with ACS Pure Parallel Observations

The ACS, with greater sensitivity and sky coverage, will extend our
ability to measure the weak gravitational lensing of galaxy images
caused by the large scale distribution of dark matter. We propose to
use the ACS in pure parallel {non- proprietary} mode, following the
guidelines of the ACS Default Pure Parallel Program. Using the HST
Medium Deep Survey WFPC2 database we have measured cosmic shear at
arc-min angular scales. The MDS image parameters, in particular the
galaxy orientations and axis ratios, are such that any residual
corrections due to errors in the PSF or jitter are much smaller than
the measured signal. This situation is in stark contrast with
ground-based observations. We have also developed a statistical
analysis procedure to derive unbiased estimates of cosmic shear from
a large number of fields, each of which has a very small number of
galaxies. We have therefore set the stage for measurements with the
ACS at fainter apparent magnitudes and smaller, 10 arc-second scales
corresponding to larger cosmological distances. We will adapt
existing MDS WFPC2 maximum likelihood galaxy image analysis
algorithms to work with the ACS. The analysis would also yield an
online database similar to that in archive.stsci.edu/mds/ 

WFPC2 9592

WFPC2 CYCLE 11 Standard Darks

This dark calibration program obtains dark frames every week in order
to provide data for the ongoing calibration of the CCD dark current
rate, and to monitor and characterize the evolution of hot pixels.
Over an extended period these data will also provide a monitor of
radiation damage to the CCDs. 

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 

WFPC2 9596

WFPC2 CYCLE 11 INTERNAL MONITOR

This calibration proposal is the Cycle 11 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.

WFPC2/ACS 9601

WFPC2-ACS Photometric Cross-Calibration

This proposal is aimed at providing photometric zeropoint
cross-calibration between the commonly used WFPC2 photometric filter
sets and those that will be used for ACS programs. The proposal
includes observations of globular clusters spanning a wide range in
metallicity, including NGC 2419 and 47 Tuc. In addition, we will
obtain WFPC2 observations of the primary ACS standard star. This
program will produce a valuable tie-in between the WFPC2, ACS and
Sloan filter photometric systems. 

STIS 9606

CCD Dark Monitor-Part 2

STIS 9608

CCD Bias Monitor - Part 2

high-S/N superbiases and track the evolution of hot columns.

STIS 9615

Cycle 11 MAMA Dark Monitor

The primary means of checking on health of the MAMA detectors systems
through frequent monitoring of the background count rate. The purpose
is to look for evidence of change in dark indicative of detector
problem developing. 

 - Continued -

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