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24 March 2003

HUBBLE SPACE TELESCOPE

DAILY REPORT       # 3325

PERIOD COVERED: DOYs 80-82

Part 3 of 6

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/HRC 9379

Near Ultraviolet Imaging of Seyfert Galaxies: Understanding the
Starburst-AGN Connection

We propose a near-UV snapshot survey of 101 Seyfert galaxies using
ACS/HRC and the filter F330W, a configuration which is optimal to
detect faint star forming regions around their nuclei. These images
will complement optical and near-IR images available in the HST
archive, thus providing a panchromatic atlas of the inner regions of
active galaxies, which we will use to study the starburst-AGN
connection. The main goals of this proposal are: {1} Determine the
frequency of circumnuclear starbursts in Seyferts, down to levels
which cannot be observed from the ground; {2} characterize the
observational {fluxes, colors, structure, sizes} and intrinsic
{luminosities, masses, ages, global star-formation rate} properties
of these clusters; {3} derive the luminosity functions of young star
clusters around the nucleus of Seyferts and compare these results
with those from normal and starburst galaxies to determine their
survival rate close to the AGN; {4} address questions about the
relation between AGNs and starbursts, like the possible connection
between the masses and luminosities of black holes and starbursts,
and the implications for the evolution of the black holes and their
host galaxy bulges. By adding UV images to the existing optical and
near-IR ones, this project will create an extremely valuable database
for astronomers with a broad range of scientific interests, from the
properties of the AGN to the properties of their host galaxies.

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/

FGS 9348

The Distances to AM CVn stars

We propose to determine the parallaxes and proper motions of the five
brightest of the seven known AM CVn systems using the HST Fine
Guidance Sensors. AM CVn systems are binaries where mass is
transferred from a completely hydrogen-deficient, degenerate mass
donor to a white dwarf primary through a helium accretion disk. A
better understanding of these systems is crucial for a number of
reasons:, to study the late stages of binary evolution, to study the
effect of chemical composition on the physics of accretion discs; , o
to estimate their contribution to the Supernovae Ia rate and , to
estimate their contribution to the gravitational radiation
background. All these studies rely critically on a determination of
the distances to the currently known systems. With brightnesses in
the range 13 * Origin: SpaceBase(tm) Pt 1 -14.4- Van BC Canada 604-473-9358 (1:153/719.1)

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