Recent systematic surveys of strong galaxy-galaxy lenses {CLASS, SLACS,
GOODS, etc.} are producing spectacular results for galaxy masses roughly
below a transition mass M~10^13 Mo. The observed lens properties and
their evolution up to z~0.2, consistent with numerical simulations, can
be described by isothermal elliptical potentials. In contrast, modeling
of giant arcs in X-ray luminous clusters {halo masses M >~10^13 Mo}
favors NFW mass profiles, suggesting that dark matter halos are not
significantly affected by baryon cooling. Until recently, lensing
surveys were neither deep nor extended enough to probe the intermediate
mass density regime, which is fundamental for understanding the assembly
of structures. The CFHT Legacy Survey now covers 125 square degrees, and
thus offers a large reservoir of strong lenses probing a large range of
mass densities up to z~1. We have extracted a list of 150 strong lenses
using the most recent CFHTLS data release via automated procedures.
Following our first SNAPSHOT proposal in cycle 15, we propose to
continue the Hubble follow-up targeting a larger list of 130 lensing
candidates. These are intermediate mass range candidates {between
galaxies and clusters} that are selected in the redshift range of 0.2-1
with no a priori X-ray selection. The HST resolution is necessary for
confirming the lensing candidates, accurate modeling of the lenses, and
probing the total mass concentration in galaxy groups up to z~1 with the
largest unbiased sample available to date.

We propose observations of the newly discovered extrasolar planet XO-2b
and its twin star XO- 2. When combined with the transit light curve, the
FGS-derived parallax will constrain the stellar mass of the host star
XO-2. From the high signal-to-noise near-IR time series resulting from
NICMOS grism spectroscopy, we will refine the system parameters, in
particular radii of the star and planet. From the same data, we will
search for evidence of water vapor in the atmosphere via transmission
spectroscopy. Differential observations with NICMOS in the spectroscopic
mode will be used to search for the small spectral changes that occur
during planetary transits resulting from absorption of stellar light as
it passes through the planetary atmosphere. Water is an important
constituent, the detection of which would provide information on Oxygen,
and it has a convenient strong band well-positioned for NICMOS.

Planetary nebulae {PNe} in globular clusters {GCs} raise a number of
interesting issues related to stellar and galactic evolution. The number
of PNe known in Milky Way GCs, 4, is surprisingly low if one assumes
that all stars pass through a PN stage. However, it is likely that the
remnants of stars now evolving in Galactic GCs leave the AGB so slowly
that any ejected nebula dissipates long before the star becomes hot
enough to ionize it. Thus there should not be ANY PNe in Milky Way
GCs--but there are four! It has been suggested that these PNe are the
result of mergers of binary stars within GCs, i.e., that they are
descendants of blue stragglers. The frequency of occurrence of PNe in
external galaxies poses more questions, because it shows a range of
almost an order of magnitude. I propose a Snapshot survey aimed at
discovering PNe in the GC systems of Local Group galaxies more distant
than the Magellanic Clouds. These clusters, some of which may be much
younger than their counterparts in the Milky Way, might contain many
more PNe than those of our own galaxy. I will use the standard technique
of emission-line and continuum imaging, which easily discloses PNe.

The current census of binaries among the massive O-type stars is
seriously incomplete for systems in the period range from years to
millennia because the radial velocity variations are too small and the
angular separations too close for easy detection. Here we propose to
discover binaries in this observational gap through a Faint Guidance
Sensor SNAP survey of relatively bright targets listed in the Galactic O
Star Catalog. Our primary goal is to determine the binary frequency
among those in the cluster/association, field, and runaway groups. The
results will help us assess the role of binaries in massive star
formation and in the processes that lead to the ejection of massive
stars from their natal clusters. The program will also lead to the
identification of new, close binaries that will be targets of long term
spectroscopic and high angular resolution observations to determine
their masses and distances. The results will also be important for the
interpretation of the spectra of suspected and newly identified binary
and multiple systems.

Filling the Period Gap for Massive Binaries

The current census of binaries among the massive O-type stars is
seriously incomplete for systems in the period range from years to
millennia because the radial velocity variations are too small and the
angular separations too close for easy detection. Here we propose to
discover binaries in this observational gap through a Faint Guidance
Sensor SNAP survey of relatively bright targets listed in the Galactic O
Star Catalog. Our primary goal is to determine the binary frequency
among those in the cluster/association, field, and runaway groups. The
results will help us assess the role of binaries in massive star
formation and in the processes that lead to the ejection of massive
stars from their natal clusters. The program will also lead to the
identification of new, close binaries that will be targets of long term
spectroscopic and high angular resolution observations to determine
their masses and distances. The results will also be important for the
interpretation of the spectra of suspected and newly identified binary
and multiple systems.

At luminosities above 10^11.4 L_sun, the space density of far-infrared
selected galaxies exceeds that of optically selected galaxies. These
Luminous Infrared Galaxies {LIRGs} are primarily interacting or merging
disk galaxies undergoing starbursts and creating/fueling central AGN. We
propose far {ACS/SBC/F140LP} and near {WFPC2/PC/F218W} UV imaging of a
sample of 27 galaxies drawn from the complete IRAS Revised Bright Galaxy
Sample {RBGS} LIRGs sample and known, from our Cycle 14 B and I-band ACS
imaging observations, to have significant numbers of bright {23 < B < 21
mag} star clusters in the central 30 arcsec. The HST UV data will be
combined with previously obtained HST, Spitzer, and GALEX images to {i}
calculate the ages of the clusters as function of merger stage, {ii}
measure the amount of UV light in massive star clusters relative to
diffuse regions of star formation, {iii} assess the feasibility of using
the UV slope to predict the far-IR luminosity {and thus the star
formation rate} both among and within IR-luminous galaxies, and {iv}
provide a much needed catalog of rest- frame UV morphologies for
comparison with rest-frame UV images of high-z LIRGs and Lyman Break
Galaxies. These observations will achieve the resolution required to
perform both detailed photometry of compact structures and spatial
correlations between UV and redder wavelengths for a physical
interpretation our IRX-Beta results. The HST UV data, combined with the
HST ACS, Spitzer, Chandra, and GALEX observations of this sample, will
result in the most comprehensive study of luminous starburst galaxies to
date.

We have constructed a sample of early type galaxies at z~0.1 that have
blue UV-optical colors, yet also show no signs of optical emission, or
extended blue light. We have cross-correlated the SDSS catalog and the
Galaxy Evolution Explorer Medium Imaging Survey to select a sample of
galaxies where this UV emission is strongest. The origin of the UV
rising flux in these galaxies continues to be debated, and the
possibility that some fraction of these galaxies may be experiencing low
levels of star formation cannot be excluded. There is also a possibility
that low level AGN activity {as evidenced by a point source} is
responsible We propose to image the UV emission using the HST/SBC and to
explore the morphology of the UV emission relative to the optical light.

The recent progress in the study of central black holes in galactic
nuclei has led to a general consensus that supermassive {10^6-10^9 solar
mass} black holes are closely connected with the formation and
evolutionary history of large galaxies, especially their bulge
component. Two outstanding issues, however, remain unresolved. Can
central black holes form in the absence of a bulge? And does the mass
function of central black holes extend below 10^6 solar masses?
Intermediate-mass black holes {<10^6 solar masses}, if they exist, may
offer important clues to the nature of the seeds of supermassive black
holes. Using the SDSS, our group has successfully uncovered a new
population of AGNs with intermediate-mass black holes that reside in
low-luminosity galaxies. However, very little is known about the
detailed morphologies or structural parameters of the host galaxies
themselves, including the crucial question of whether they have bulges
or not. Surprisingly, the majority of the targets of our Cycle 14 pilot
program have structural properties similar to dwarf elliptical galaxies.
The statistics from this initial study, however, are really too sparse
to reach definitive conclusions on this important new class of black
holes. We wish to extend this study to a larger sample, by using the
Snapshot mode to obtain WFPC2 F814W images from a parent sample of 175
AGNs with intermediate- mass black holes selected from our final SDSS
search. We are particularly keen to determine whether the hosts contain
bulges, and if so, how the fundamental plane properties of the host
depend on the mass of their central black holes. We will also
investigate the environment of this unique class of AGNs.

The discovery of binaries in the Kuiper Belt and related small body
populations is powering a revolutionary step forward in the study of
this remote region. Three quarters of the known binaries in the Kuiper
Belt have been discovered with HST, most by our snapshot surveys. The
statistics derived from this work are beginning to yield surprising and
unexpected results. We have found a strong concentration of binaries
among low-inclination Classicals, a possible size cutoff to binaries
among the Centaurs, an apparent preference for nearly equal mass
binaries, and a strong increase in the number of binaries at small
separations. We propose to continue this successful program in Cycle 16;
we expect to discover at least 13 new binary systems, targeted to
subgroups where these discoveries can have the greatest impact.

We propose to obtain images of 13 relatively luminous early type
galaxies in the Coma cluster and Abell 262 for which we have already
collected ground based major and minor axis spectra and images. The
higher resolution HST images will enable us to study the central regions
of these galaxies which is crucial to our dynamical modelling. The
complete data set will allow us to perform a full dynamical analysis and
to derive the dark matter content and distribution, the stellar orbital
structure, and the stellar population properties of these objects,
probing the predictions of galaxy formation models. The dynamical
analysis will be performed using an up-to- date axi-symmetric orbit
superposition code.

HSTARS:
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