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Cycle
16 Abstract catalog (based on Phase I submissions) Generated
on:
Mon
Apr 9 12:08:20 EDT 2007 ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11099 Title:
A
"silver bullet" for the sources of reionization PI:
Marusa
Bradac PI
Institution:
Stanford
University Recent
discoveries of z>6 galaxies have given us the first glimpse of the Universe
shortly after the era of reionization. The questions arose whether these
first galaxies can be made responsible for the reionization process, and how
long did it last. Neither observations nor theory provide a clean
answer. In
particular observations give results that are barely mutually consistent and
need to be further tested. Observing high redshift (z>7) sources is
in general
difficult, mostly due to the high luminosity distance to these objects,
and partly due to the lower expected stellar masses compared to objects
at moderate redshifts. We
propose to use one of the most massive, merging
cluster 1E0657-56 (z=0.295) as a cosmic telescopes to efficiently probe
the high-redshift universe. The gravitational potential well of this cluster
provides several magnitudes of magnification, enabling study of intrinsically
lower luminosity galaxies.As we discuss in the proposal, due to its
highly elongated mass distribution and ideal redshift the bullet cluster is
a prime candidate for this study. We propose deep NICMOS and WFPC2 observations;
with much reduced observing time compared to e.g. NICMOS UDF we expect
an order of magnitude more (~5 candidates) z>7 objects. They will
also likely
be multiply imaged, and since the geometry of images depends upon the redshift,
we will be able to confirm their nature, thereby not requiring (often
prohibitive at these magnitudes) spectroscopic follow-up. This will enable
us to count high-redshift sources and constrain their luminosity function;
a task made possible with the help of gravitational lensing even in the
pre-JWST era. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11100 Title:
Two
new `bullets' for MOND: revealing the properties of dark matter in
massive
merging clusters PI:
Marusa
Bradac PI
Institution:
Stanford
University The
principal objective of this proposal is to study the physical nature of dark
matter by using two, massive, newly-identified merging clusters of galaxies.
As shown by the pioneering example of the ``bullet cluster'' (1E0657-56),
such systems are ideal laboratories for detecting dark matter and distinguishing
between cold dark matter (CDM) and other scenarios (e.g.
self- interacting
dark matter). Our limit on the self-interaction cross-section of dark
matter relies on the assumption of a normal pre-merger mass-to-light ratios,
and a small impact parameter during the collision of the two clusters. In
order to mitigate any possible systematic effects, it is vital to extend this
work to other, similar systems. With detailed observations of new systems,
the systematic uncertainties in the dark matter cross section calculations
can be improved substantially, allowing us to move from rough order
of magnitude estimates to measurements with quantifiable uncertainties that
can be compared usefully with the predictions from numerical
simulations. Our
targets are two extraordinary, high-redshift, merging galaxy clusters recently
discovered by the Massive Cluster Survey (MACS). This
survey is by far
the best matched to this study, since it selects medium redshift
(optimal for
gravitational lensing studies) and X-ray luminous (hence massive)
objects. We
have selected the best candidates with clear evidence for considerable offsets
between the hot X-ray emitting gas and optically luminous stellar material.
The two most striking examples are the targets of this proposal. To pin
down the position of the dark matter component we require high
resolution, absolutely
calibrated mass maps. The combination of weak and strong lensing measurements
is needed to attain this goal. This can only be achieved with the excellent
resolving power of the HST (in combination with wide-field, multicolor
Subaru data already in hand). We
therefore request multicolor HST/WFPC2
observations of the two merging clusters. The combination of constraints
from multiply lensed images (identified via morphology and color information)
and high-resolution weak lensing data will allow us to construct, self-consistently,
their mass distribution from the very centers to the outskirts.
Gravitational lensing thus provides a unique tool transforming these
clusters into dark matter laboratories. They will supply us with answers as
to the nature and properties of dark matter, and how it shapes galaxies
and galaxy
clusters and their evolution through cosmic time. ====================================================================== Proposal
Category: GO Scientific
Category: AGN/QUASARS ID:
11101 Title:
The
Relevance of Mergers for Fueling AGNs: Answers from QSO Host Galaxies PI:
Gabriela
Canalizo PI
Institution:
University
of California - Riverside The
majority of QSOs are known to reside in centers of galaxies that look
like ellipticals.
Numerical simulations have shown that remnants of galaxy mergers often
closely resemble elliptical galaxies. However, it is still strongly debated
whether the majority of QSO host galaxies are indeed the result of relatively
recent mergers or whether they are completely analogous to inactive ellipticals
to which nothing interesting has happened recently.
To address this
question, we recently obtained deep HST ACS images for five QSO host galaxies
that were classified morphologically as ellipticals (GO-10421). This pilot
study revealed striking signs of tidal interactions such as ripples, tidal
tails, and warped disks that were not detected in previous studies. Our observations
show that at least some "elliptical" QSO host galaxies are the products
of relatively recent merger events rather than old galaxies formed at high
redshift. However, the question remains whether the host galaxies of classical
QSOs are truly distinct from inactive ellipticals and whether there is
a connection between the merger events we detect and the current nuclear activity.
We must therefore place our results into a larger statistical context.
We are currently conducting an HST archival study of inactive elliptical
galaxies (AR-10941) to form a control sample. We now propose to obtain
deep HST/WFPC2 images of 13 QSOs whose host galaxies are classified as normal
ellipticals. Comparing the results for both samples will help us determine
whether classical QSOs reside in normal elliptical galaxies or not. Our
recent pilot study of five QSOs indicates that we can expect exciting results
and deep insights into the host galaxy morphology also for this larger sample
of QSOs. A statistically meaningful sample will help us determine the true
fraction of QSO hosts that suffered strong tidal interactions and thus, whether
a merger is indeed a requirement to trigger nuclear activity in the most
luminous AGNs. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11102 Title:
HST
as a Jovian Climate Satellite PI:
Imke
de Pater PI
Institution:
University
of California - Berkeley In
the past year, there have been striking changes in Jupiter's atmosphere. Among
these are the Oval BA's change from white to red, two new dark Disturbances
in the southern hemisphere, and a 30% change (since 1997) in the aspect
ratio of the potential vorticity anomaly of the GRS (not just its associated
clouds), as we determined from high-accuracy velocities extracted from
HST images. The determination of high-accuracy velocities requires both high-resolution
imaging by HST (or flybys), and our novel adaptation of Correlation
Image Velocimetry (CIV), a technique that has far greater accuracy than
the traditional method (of identifying velocity tie-points by hand). Our proposed
observations will test the hypothesis that these changes in Jupiter validate
our 2004 prediction:
that
the merger of the 3 White Ovals in 1998- 2000
would lead to climate change on Jupiter. The key is to determine, by indirect
means, the temperature at the base of
the weather layer, a quantity that
cannot be observed directly at any wavelength. The new Red Oval BA's velocities
will be used to test our finding that the color change is due to global
temperature changes. The change in the GRS's aspect ratio suggests a large
(at least 20%) change in the shear of the local velocity since 1997. The latter
can be investigated only by determining Jupiter's current zonal winds. ====================================================================== Proposal
Category: SNAP Scientific
Category: COSMOLOGY ID:
11103 Title:
A Snapshot Survey of The Most
Massive
Clusters of Galaxies PI:
Harald
Ebeling PI
Institution:
University
of Hawaii We
propose the continuation of our highly successful SNAPshot survey of a sample
of 125 very X-ray luminous clusters in the redshift range 0.3-0.7. As demonstrated
by the 25 snapshots obtained so far in Cycle14 and Cycle15 these systems
frequently exhibit strong gravitational lensing as well as spectacular examples
of violent galaxy interactions. The proposed observations will provide
important constraints on the cluster mass distributions, the physical nature
of galaxy-galaxy and galaxy-gas interactions in cluster cores, and a set
of optically bright, lensed galaxies for further 8-10m spectroscopy. All of
our primary science goals require only the detection and
characterisation of
high-surface-brightness features and are thus achievable even at the reduced
sensitivity of WFPC2. Because of their high redshift and thus compact angular
scale our target clusters are less adversely affected by the smaller field
of view of WFPC2 than more nearby systems. Acknowledging the broad community
interest in this sample we waive our data rights for these observations. Due to a clerical error at STScI
our approved Cycle15 SNAP program
was barred from execution for 3 months and only 6 observations have been
performed to date - reinstating this SNAP at Cycle16 priority is of paramount
importance to reach meaningful statistics. ====================================================================== Proposal
Category: GO Scientific
Category: AGN/QUASARS ID:
11104 Title:
The
nature of radio transients PI:
Avishay
Gal-Yam PI
Institution:
California
Institute of Technology We
have conducted the first ever blind, wide-field survey for radio
transients (Levinson
et al. 2002; Gal-Yam et al. 2006). We have discovered four radio transients
and explored their nature using radio and optical follow-up observations.
One is a known pulsar, one is a z~0.1 AGN, and one is most probably
an optically obscured radio supernova (SN) in the nearby galaxy NGC 4216
(the first such event to be discovered by a wide field radio survey).
The last
source appears not to be associated with a bright host galaxy (to a
limit of
R < 24.5 mag). We request 4 orbits of WFPC2 F606W imaging to check
whether we
can establish an association between this radio transient and any of
three nearby
faint resolved galaxies we have detected from the ground. If the source is
associated with any of these galaxies it would represent a new type of extra-galactic
radio bursts, more luminous than, e.g., radio afterglows of gamma-ray
bursts. Alternatively, ruling out an association with these galaxies would
disfavor an extra-galactic nature of this object, and suggest instead that
this is a radio outburst of a faint Galactic compact object, probably a new
type of radio-flaring neutron star. If this is the case, the high luminosity
(9 mJy) and relatively high galactic latitude (33 degrees) of this source
may indicate it is relatively nearby. This single source represents a large
population (comparable in sky density to AGN, pulsars, and radio SNe) and
thus merits intensive study. A modest investment of HST time, leveraged
by massive
ground-based radio and optical efforts, will allow us to identify a new
class of radio sources, and complete a census of the variable radio sky down
to ~6 mJy, leaving no unidentifed objects. This result can be directly scaled
to predict the number and type of transient sources expected to be detected
by future surveys with the next generation radio arrays, such as ATA and
SKA.Since our science critically requires HST's spatial resolution
(rather than
sensitivity) it is perfectly suited to be carried out with WFPC2. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11105 Title:
The
LBV progenitor of SN 2005gl - a new key to massive star evolution
puzzles PI:
Avishay
Gal-Yam PI
Institution:
California
Institute of Technology The
currently accepted theory regarding the last stages of massive star evolution
maintains that the evolution of the envelope is coupled to that of the
stellar core. For this reason, very massive stars are expected to shed their
outer hydrogen envelopes before they develop large iron cores, and ultimately,
explode as core-collapse supernovae (SNe). It is therefore a strict
prediction of current models that massive stars (certainly those above ~40
solar mass) will explode as hydrogen-poor SNe, i.e., of Types Ib and Ic. In
particular, the class of luminous blue variables (LBVs) such as
eta-Carina, which
are known to be very massive (up to 100 solar masses and above) are expected
to lose their entire hydrogen envelopes prior to their ultimate explosions
as SNe. However, using pre-explosion HST/WFPC2 imaging of the location
of the recent hydrogen-rich type IIn SN 2005gl, we have identified (Gal-Yam
et al. 2007) its putative progenitor as a very luminous point source (with
absolute V magnitude of -10.2). If this is a single star, it must be an LBV
from luminosity considerations (no other stars are as luminous). If our progenitor
identification is correct, at least in some cases, massive stars explode
before losing most of their hydrogen envelope, indicating the core and envelope
are decoupled, and requiring revision of stellar evolution theory. Here,
we propose a single-orbit HST observation of the location of SN 2005gl designed
to test whether the point source we identified as its LBV progenitor has
indeed disappeared (as expected from a single star) or remained
unchanged (as
expected, e.g., if it is a compact star cluster). These data are the
last observational
ingredient required to firmly establish (or refute) the explosion
of an LBV as a type IIn SN, with fundamental implications for the theory
of massive star evolution. Since the new data will be compared to pre- explosion
WFPC2 images, this program is perfectly suited to be carried out with
the WFPC2 camera. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11106 Title:
Target
of Opportunity Imaging of an Unusual Cloud Feature on Uranus PI:
Heidi
Hammel PI
Institution:
Space
Science Institute The
planet Uranus is demonstrating increased atmospheric activity as it approaches
its 2007 equinox, perhaps in response to extreme insolation change. Convective
sites in the planet's southern hemisphere reached unprecedented altitudes
in 2003 (Hammel et al. 2005, Icarus 175, 284); a bright northern feature
showed the highest contrast yet detected in an outer planet atmosphere (Sromovsky
et al. 2007, Icarus, submitted); and a dark atmospheric feature was detected
by HST for the first time (Hammel et al. 2007, in preparation). The historical
record makes references to discrete structures (both bright and dark)
on Uranus during previous equinoctial apparitions (the last equinox occurred
in 1965). The best amateur
facilities are now just able to resolve the
disk of Uranus and detect such activity if it is very large or has very high
contrast. Amateurs also have
access to a great many nights of telescope time. If a discrete cloud feature on Uranus
is reported through the amateur network,
we propose to obtain follow-up images with HST's WFPC2.
The proposed TOO
images will permit determination of detailed structure of the feature at visible
wavelengths, and will provide vertical and horizontal constraints on the
feature's scattering properties.
HST is the only facility that can provide
such information at visible wavelengths. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11107 Title:
Imaging
of Local Lyman Break Galaxy Analogs: New Clues to Galaxy Formation in
the Early
Universe PI:
Timothy
Heckman PI
Institution:
The
Johns Hopkins University We
have used the ultraviolet all-sky imaging survey currently being
conducted by
the Galaxy Evolution Explorer (GALEX) to identify for the first time a
rare population
of low-redshift starbursts with properties remarkably similar to high-redshift
Lyman Break Galaxies (LBGs). These "compact UV luminous galaxies"
(UVLGs) resemble LBGs in terms of size, SFR, surface brightness, mass,
metallicity, kinematics, dust, and color. The UVLG sample offers the unique
opportunity of investigating some very important properties of LBGs that
have remained virtually inaccessible at high redshift:
their morphology and
the mechanism that drives their star formation. Therefore, in Cycle 15
we have
imaged 7 UVLGs using ACS in order to 1) characterize their morphology
and look
for signs of interactions and mergers, and 2) probe their star formation histories
over a variety of timescales. The images show a striking trend of small-scale
mergers turning large amounts of gas into vigorous starbursts (a process
referred to as dissipational or "wet" merging). Here, we propose to complete
our sample of 31 LBG analogs using the ACS/SBC F150LP (FUV) and WFPC2 F606W
(R) filters in order to create a statistical sample to study the mechanism
that triggers star formation in UVLGs and its implications for the nature
of LBGs. Specifically, we will 1) study the trend between galaxy merging
and SFR in UVLGs, 2) artificially redshift the FUV images to z=1-4 and compare
morphologies with those in similarly sized samples of LBGs at the same rest-frame
wavelenghts in e.g. GOODS, UDF, and COSMOS, 3) determine the presence
and morphology of significant stellar mass in "pre-burst" stars, and 4)
study their immediate environment. Together with our Spitzer
(IRAC+MIPS), GALEX,
SDSS and radio data, the HST observations will form a unique union of data
that may for the first time shed light on how the earliest major
episodes of
star formation in high redshift galaxies came about.
This proposal was adapted
from an ACS HRC+WFC proposal to meet the new Cycle 16 observing constraints,
and can be carried out using the ACS/SBC and WFPC2 without compromising
our original science goals. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11108 Title:
Near
Infrared Observations of a Sample of z~6.5-6.7 Galaxies PI:
Esther
Hu PI
Institution:
University
of Hawaii The
majority of the most distant galaxies discovered to date have been found by
strong Lyman alpha emission at red optical wavelengths.
An accurate estimate
of the star formation rates for
these objects requires a measurement of
the line-free UV continuum, which must be taken at infrared wavelengths. Here
we propose to obtain imaging with NICMOS in the F160W filter for a
sample of
9 Lyman alpha galaxies with redshifts z~6.5 up to z=6.740 from a
complete, flux-limited
widefield narrowband and multi-color survey conducted on the 8-m Subaru
Telescope. This program will investigate galaxy morphologies and star formation
for a uniform sample of the highest redshift galaxies now known. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11109 Title:
Characterization
of the UV absorption feature in asteroid (1) Ceres PI:
Jianyang
Li PI
Institution:
University
of Maryland We
propose to obtain the UV spectrum of asteroid (1) Ceres from 120 nm to
200 nm
with ACS/SBC objective prism to characterize the broad and deep
absorption feature
within this wavelength range as reported recently.
Our scientific goals
include, 1) to characterize the absorption band, 2) to determine the origin
of this spectral feature and constrain the surface compositions of Ceres,
and 3) to understand the albedo and color features on Ceres. HST is the
only observatory currently capable of obtaining spectroscopy in this wavelength
range. This observation will help
improve our knowledge about this largest
and oldest asteroid, and support the planning of the upcoming NASA Discovery
Program mission, Dawn, orbiting asteroids Vesta and Ceres. ====================================================================== Proposal
Category: GO Scientific
Category: ISM IN EXTERNAL GALAXIES ID:
11110 Title:
Searching
for Lyman alpha Emission from FUSE Lyman Continuum Candidates PI:
Stephan
McCandliss PI
Institution:
The
Johns Hopkins University We
have recently been granted time on FUSE to characterize the escape
fraction of
hydrogen Lyman continuum (Lyc) photons from a morphologically diverse
set of
star forming galaxies. The FUSE
program is designed to provide ~ 5 sigma detections
of Lyc photons emitted from star
forming galaxies with escape fractions
~5%. With this proposal we seek
hydrogen Lyman alpha (Lya) observations
of a representative subset of the FUSE program targets to constrain
the observational relationship between Lyc, Lya, and hydrogen Balmer line
emission in these systems. Such
observations explore the detailed balance
between the simple optically thin (Case A) and optically thick (Case B)
limits in recombination theory.
The ultimate goal of this program is to quantify
the relationship between escaping Lya and Lyc emission and the first structures
that form in the early universe. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11111 Title:
A
Search for an Intermediate Mass Black Hole in the Globular Cluster NGC
6266 PI:
Bernard
McNamara PI
Institution:
New
Mexico State University We
propose to search for an intermediate mass black hole (IMBH) in the
core of the
galactic globular cluster NGC 6266. Based on a comparison between the observed
central surface brightness profiles of 38 globular clusters and state-of-the
art N-body simultations, NGC 6266 offers the best hope of detecting
an IMBH among these objects. This detection would be significnat for at
least two reasons. It would be the first concrete discovery of an IMBH, revealing
unique information about the environment in which these objects form,
and second, its discovery would provide a powerful validation on the N- body
simultations used to track the dynamical evolution of globular clusters. ====================================================================== Proposal
Category: GO Scientific
Category: UNRESOLVED STELLAR POPULATIONS ID:
11112 Title:
The
Collisional Ring Galaxy NGC922 PI:
Gerhardt
Meurer PI
Institution:
The
Johns Hopkins University We
request WFPC2 images of the newly recognized collisional ring galaxy
NGC922 which
will become the nearest such system observed by HST. These will be used to
get a clear understanding of the geometry of the interaction and the induced
star formation in this system.
Quantitive modeling of the colors of the
star clusters and stellar populations will be used to constrain the star formation
history of the system. They will
also be used to test the "infant mortality"
scenario for star cluster evolution. The derived population ages will
test predictions of how star formation evolves in the various components (ring,
core, spokes) of collisional rings, and will improve our own simulations
of this system. These will be used
to determine the final fate of the
stars formed in the present burst - some will end up in a central bar or bulge
while others will become part of a thickened disk.
By analogy this will tell
us how similar collisions enrich stellar populations in the early universe. This is especially relevant since the
number density of collisional rings
increases rapidly with redshift. ====================================================================== Proposal
Category: SNAP Scientific
Category: SOLAR SYSTEM ID:
11113 Title:
Binaries
in the Kuiper Belt:
Probes
of Solar System Formation and Evolution PI:
Keith
Noll PI
Institution:
Space
Telescope Science Institute 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. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11114 Title:
Improving
proper motion measurements of the
stars in the field of SN 1572 with WFPC2 PI:
Pilar
Ruiz-Lapuente PI
Institution:
Universidad
de Barcelona We
propose to complete the spatial velocity measurements of the stars in
the central
region of the remnant of SN 1572, one of the historical Galactic Type Ia
supernovae. A new visit with WFPC2 would allow us to significantly
improve the
accuracy of the proper motion measurements of the stars in the field, since
we would benefit from a long temporal baseline by using the WFPC2 images previously
taken. This unique legacy would complement the high-precision ground-based
observations made for the stars in the SN 1572 field during the past
ten years. The search for the companion star of Galactic Type Ia supernovae,
based on their high peculiar velocity as a salient feature, has already
pointed to a good candidate for SN 1572. The current uncertainties in the
tangential velocity of the candidate star and the other stars in the
field can
be reduced to less than a half with a visit in Cycle 16. This would lead to
a precise determination of the parameters of the binary system that gave rise
to the supernova. If not done during Cycle 16, the long temporal
baseline for
SN 1572 with WFPC2 would be lost. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11115 Title:
Photometric
Imaging of Asteroid 2 Pallas PI:
Christopher
Russell PI
Institution:
University
of California - Los Angeles We
propose to conduct the first HST imaging of Asteroid 2 Pallas with
WFPC2-PC over
8 HST orbits. We will image the
asteroid in five filters: F336w,
F439w, F555w,
F675w and F814w. We will utilize
these observations to drastically improve
the knowledge of Pallas' shape, spin pole position and surface properties,
including roughness and albedo, parameters that are poorly determined
by previous study. These observations will result in high signal- to-noise,
high resolution surface maps from the visible to the UV.
A satellite
search will also be conducted for objects within the stability field of
up to 21st magnitude, or about 900m in diameter. It
is demonstrated in our proposal
that significant scientific opportunity exists in Cycle 16 because Pallas
is at both a low-phase, 3.9 degree opposition and near its closest approach
to Earth, conditions that do not occur simultaneously in the next twenty
years. This window represents the
best chance to answer long standing, fundamental
questions about Pallas, the main asteroid belt, and the formation of
the solar system. ====================================================================== Proposal
Category: GO Scientific
Category: COOL STARS ID:
11116 Title:
Exploring
the Early FUV History of Cool Stars: Transition Regions at 30 Myr PI:
Steven
Saar PI
Institution:
Smithsonian
Institution Astrophysical Observatory Stellar
magnetic activity derives from the so-called "dynamo," a
hydromagnetic interplay
between overturning plasma motions and differential rotation in stars
cool enough to support significant surface convection zones. The magnetic
fields resulting from dynamo action are in turn are responsible for a wide
range of high-energy emissions, including the spectacular outbursts called
flares. Dynamo powered magnetic
activity is not confined solely to stars,
but also must occur, for example, in accretion disks of all descriptions,
and in some planets. A great deal
is known about magnetic activity
in middle-aged G dwarfs like our Sun, thanks to its proximity. Less is
known, however, about the much younger stars, newly emerged from the T- Tauri
stage. Yet, it is during this
phase that they reach the peak of their magnetic
activity, and subsidiary influences, such as the impact of ionizing radiation
and strong coronal winds on developing solar systems, also are maximum. One of the key missing ingredients in
our current understanding are measurements
of FUV emissions of such stars, to complement the extensive collections
of coronal (1-10 MK) X-ray measurements, particularly from recent ROSAT,
Chandra and XMM-Newton surveys. We
propose to conduct sensitive ACS/SBC
prism ultraviolet spectroscopy of selected fields in two young (30 Myr)
Galactic clusters--IC 2391 and IC 2602--to inventory the key C IV emission
index (~0.1 MK) over a much larger and more diverse sample of coeval objects
than has been possible hitherto. A
key question is whether the FUV emissions
also suffer the "saturation" and "super-saturation" at
short rotation
periods seen in coronal X-rays, or whether they continue to rise in the
fastest rotating stars. The
saturation behavior of the different temperature
regimes holds important clues to the organization of the surface active
regions on these very young stars, and should allow us to distinguish among
several competing models. ====================================================================== Proposal
Category: GO Scientific
Category: STAR FORMATION ID:
11117 Title:
The
Search for Atmospheric Water in the Transiting Planet HD189733b PI:
David
Sing PI
Institution:
CNRS,
Institut d'Astrophysique de Paris We
propose to use the NICMOS camera to search for transit NIR signatures of atmospheric
water in HD189733b. While water
absorption bands exist in the optical
and IR, space-based NIR signatures are uniquely positioned to offer the
best chance at detection. Using
narrow band photometric filters, we will be
able to detect absorption signatures while the planet is in primary transit. A positive detection would be the first
proof of water on an extrasolar
planet. Furthermore, it would
provide invaluable planetary information,
constraining the entire chemistry.
As a byproduct of the high SNR
required for our primary science goal, we will be able to improve on the value
of the planetary radius, a result independent of our primary science objective. The accurate radius estimate, together
with planet structure models,
will allow constraining the planet interior and its relationship with formation
models and stellar metallicity. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11118 Title:
Investigating
Near-Equinox Atmospheric Change on Uranus PI:
Lawrence
Sromovsky PI
Institution:
University
of Wisconsin - Madison Uranus
is approaching its 7 December 2007 equinox, when we will be able to observe
the entire northern hemisphere for the first time with modern cameras. The
large seasonal phase shift expected from its long radiative time
constant implies
that it should now exhibit nearly maximal hemispheric contrast, and should
be in the process of reversing.
Many changes already observed, such as the
development of the first visible-wavelength dark spot, discovered in
Cycle 15,
and the fading of the south polar cap may be indicative of the expected reversal. We propose a detailed characterization
of Uranus' current seasonal response
with a 7-orbit program consisting of 1 orbit of NICMOS imaging of cloud
bands and 6 orbits of WFPC2 imaging using both broadband and narrow-band filters
capable of tracking dark and bright discrete cloud features. Filters between
0.467 and 1.87 microns will provide vertical sensing depths scanning through
the pressure range where the putative methane and deeper H2S clouds might
plausibly exist and provide strong constraints on their contributions and
parent gas mixing ratios. These
observations have unique combinations of spectral
range and resolution with needed temporal and spatial resolution not available
from groundbased observations. Only HST is capable of investigating the
Uranus dark spot. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11119 Title:
The
Stellar Origins of Supernovae PI:
Schuyler
Van Dyk PI
Institution:
Jet
Propulsion Laboratory Supernovae
(SNe) have a profound effect on galaxies, and have been used recently
as precise cosmological probes, resulting in the discovery of the accelerating
Universe. They are clearly very
important events deserving of intense
study. Yet, even with nearly 4000
known SNe, we know relatively little
about the stars which give rise to these powerful explosions. The main limitation
has been the lack of spatial resolution in pre-SN imaging data. However,
since 1999 our team has been at the vanguard of directly identifying SN
progenitor stars in HST images.
From this exciting new line of study, the emerging
trend from 5 detections for Type II-Plateau SNe is that their progenitors
appear to be relatively low mass (8 to 20 Msun) red supergiants, although
more cases are needed.
Nonetheless, the nature of the progenitors of Type
Ib/c SNe, a subset of which are associated with the amazing gamma-ray bursts,
remains ambiguous. Furthermore, we
remain in the continually embarrassing
situation that we still do not yet know which progenitor systems explode
as Type Ia SNe, which are currently being used for precision cosmology. We propose to confirm the identities of
the progenitors of 4 SNe within
17 Mpc, which we expect to occur during Cycle 16, through ToO observations
using WFPC2/PC. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11120 Title:
A
Paschen-Alpha Study of Massive Stars and the ISM in the Galactic Center PI:
Daniel
Wang PI
Institution:
University
of Massachusetts The
Galactic center (GC) is a unique site for a detailed study of a
multitude of
complex astrophysical phenomena, which may be common to nuclear regions
of many
galaxies. Observable at resolutions unapproachable in other galaxies,
the GC
provides an unparalleled opportunity to improve our understanding of the interrelationships
of massive stars, young stellar clusters, warm and hot ionized
gases, molecular clouds, large scale magnetic fields, and black holes. We
propose the first large-scale hydrogen Paschen alpha line survey of the
GC using
NICMOS on the Hubble Space Telescope. This survey will lead to a high resolution
and high sensitivity map of the Paschen alpha line emission in addition
to a map of foreground extinction, made by comparing Paschen alpha to radio
emission. This survey of the inner 75 pc of the Galaxy will provide an unprecedented
and complete search for sites of massive star formation. In particular,
we will be able to (1) uncover the distribution of young massive stars
in this region, (2) locate the surfaces of adjacent molecular clouds, (3)
determine important physical parameters of the ionized gas, (4) identify compact
and ultra-compact HII regions throughout the GC. When combined with existing
Chandra and Spitzer surveys as well as a wealth of other multi- wavelength
observations, the results will allow us to address such questions as
where and how massive stars form, how stellar clusters are disrupted,
how massive
stars shape and heat the surrounding medium, and how various phases of this
medium are interspersed. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11121 Title:
Proper
Motion of the Remarkable Irradiated Jet HH399 in the Trifid Nebula PI:
Farhad
Yusef-Zadeh PI
Institution:
Northwestern
University The
Trifid nebula has recently been of much interest because of its identification
with a large number of massive protostars, as well as young stellar
objects. HH 399 is one of the most spectacular Herbig-Haro flows recognized
to be irradiated by the UV flux of the massive O7.5 star in the Trifid
nebula. The irradiated jet, which is propagating in a fully ionized medium,
contains numerous knots along the jet and also shows evidence for a number
of isolated knots running immediately outside the jet. Two different HST
observations of the nebula, with different scientific goals, were
carried out
in 1997 and 2002, having sensitivities that differed by a factor of 10.
We performed
preliminary proper motion measurements of the jet based on these observations
and discovered a continuous velocity structure of the bright knots
of about 230 km/sec. Here we propose four WFPC2 orbits to reobserve HH 399
in order to carry out accurate proper motion measurements over the full extent
of the jet, based on observations spanning more than 10 years and having
equally deep sensitivity. The proposed observations are not simply a repeat
of previous measurements, as this will be the first highly accurate proper
motion measurement of an irradiated jet based on two identical epochs of
WFPC2 observations. The observations will improve the accuracy of proper motion
measurements for HH 399 by more than a factor of five and will address important
questions beyond our preliminary result. Currently measured velocity differences
between the jet features are barely significant. The factor of 5 increase
in accuracy will establish the evidence for deceleration along the jet
and the lateral motion of the jet. In addition, these measurements will address
the kinematics of individual entrained and isolated blobs of the jet as
it propagates into an HII region associated with the nebula. This is the last
opportunity to perform this experiment before WFPC2 is removed from HST. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11122 Title:
Expanding
PNe: Distances and Hydro Models PI:
Bruce
Balick PI
Institution:
University
of Washington We
propose to obtain repeat narrowband images of a sample of eighteen planetary
nebulae (PNe) which have HST/WFPC2 archival data spanning time baselines
of a decade. All of these targets
have previous high signal-to- noise
WFPC2/PC observations and are sufficiently nearby to have readily detectable
expansion signatures after a few years.
Our main scientific objectives
are (a) to determine precise distances to these PNe based on their angular
expansions, (b) to test detailed and highly successful hydrodynamic models
that predict nebular morphologies and expansions for subsamples of round/elliptical
and axisymmetric PNe, and (c) to monitor the proper motions of
nebular microstructures in an effort to learn more about their physical nature
and formation mechanisms. The proposed
observations will result in high-precision
distances to a healthy subsample of PNe, and from this their expansion
ages, luminosities, CSPN properties, and masses of their ionized cores. With good distances and our hydro
models, we will be able to determine fundamental
parameters (such as nebular and central star masses, luminosity, age). The same images allow us to monitor the
changing overall ionization state
and to search for the surprisingly non-homologous growth patterns to bright
elliptical PNe of the same sort seen by Balick & Hajian (2004) in
NGC 6543. Non-uniform growth is a sure sign of
active pressure imbalances within the
nebula that require careful hydro models to understand. ====================================================================== Proposal
Category: GO Scientific
Category: STAR FORMATION ID:
11123 Title:
A
NICMOS Survey for Proplyds in the RCW 38 Massive Embedded Cluster PI:
Tyler
Bourke PI
Institution:
Smithsonian
Institution Astrophysical Observatory We
propose a search for line emission from photoevaporating protoplanetary disks
in the Massive Embedded Cluster
RCW 38. These disks would be analogous to
the "proplyds" discovered in the Orion Nebula:
disks around young low
mass stars
which are being photoionized by a nearby O star. We
will search for these
disks in RCW 38 using narrowband imaging in the lines of Paschen alpha and
molecular hydrogen (1-0) S(1) with NICMOS. The
RCW 38 region is an excellent
target for determining whether proplyds are observable
in large numbers
outside of Orion. It is a young
embedded cluster hosting a few hundred
low mass young stars with a large percentage showing infrared excess indicating
the presence of disks. About 100
of these stars are found within 0.1
pc of the central O5 star, and the cluster is located within a cleared cavity
0.2 pc in size, embedded within a
molecular cloud, exposing the cluster
members directly to the UV radiation from the O star.
Unlike Orion, but
like many other young clusters, RCW 38 is not seen in visible light, and infrared
imaging is needed. The best line
in the infrared for revealing proplyds
is the Paschen alpha line, which is not detectable from the ground. Only
HST is able to perform these observations. From
these observations we will
estimate the lifetime of the evaporating disks, and ascertain whether these
disks will survive long enough to form planets. ====================================================================== Proposal
Category: GO Scientific
Category: QUASAR ABSORPTION LINES AND IGM ID:
11124 Title:
The
Origin of QSO Absorption Lines from QSOs PI:
David
Bowen PI
Institution:
Princeton
University We
propose using WFPC2 to image the fields of 10 redshift z ~ 0.7
foreground (FG)
QSOs which lie within ~29-151 kpc of the sightlines to high-z background (BG)
QSOs. A surprisingly high fraction of the BG QSO spectra show strong
MgII (2796,2803)
absorption lines at precisely the same redshifts as the FG QSOs. The
high resolution capabilities of WFPC2 are needed to understand the
origin of
these absorption systems, in two ways.
First, we wish to explore the FG QSO
environment as close as possible to the position of the BG QSO, to
search for
interloping group or cluster galaxies which might be responsible for the absorption,
or irregularly shaped post-merger debris between the FG and BG QSO which
may indicate the presence of large amount of disrupted gas along a sightline.
Similarly, high resolution images are needed to search for signs of tidal
interactions between any galaxies which might be found close to the FG QSO.
Such features might provide evidence of young merging events causing the start
of QSO duty cycles and producing outflows from the central AGN. Such winds
may be responsible for the observed absorption lines.
Second, we seek to
measure the intrinsic parameters of the FG QSO host galaxy, such as luminosity
and morphology, to correlate with the properties of the MgII absorption
lines. We wish to observe each
field through the F814W filter, close
to the rest-frame B-band of the FG QSO. These blue data can reveal enhanced
star formation regions close to the nucleus of the host galaxy, which may
be indicative of galaxy mergers with the FG QSO host. The FG QSO environment
offers quite a different set of phenomena which might be responsible
for MgII absorption, providing an important comparison to studies of
MgII absorption from regular field galaxies. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11125 Title:
The
Dynamical Evolution of Globular Clusters PI:
Joel
Bregman PI
Institution:
University
of Michigan Globular
clusters evolve through dynamical interactions, with primordial binaries
extending the time until core collapse by up to an order of magnitude,
depending on the initial binary fraction.
These dynamical interactions
plus mass segregation causes the binary fraction to rise in the core
but fall at larger radii. We hope
to eventually test these broad predictions
by comparing them to the binary properties for globular clusters at
different states of evolution, defined by the ratio of their age to the dynamical
relaxation time at the half-light radius.
The most important unknown
aspects in the modeling process are the initial conditions of binaries in
the cluster. Here we propose to
determine the initial binary fraction as a function
of radius by studying three of the dynamically youngest globular clusters
(NGC 5053, NGC 5466, and NGC 5897).
The presence of binaries thickens
the Main Sequence in a color-magnitude diagram, which can be detected with
deep multicolor images. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11126 Title:
Resolving
the Smallest Galaxies PI:
Kristin
Chiboucas PI
Institution:
University
of Hawaii An
order of magnitude more dwarf galaxies are expected to inhabit the Local Group,
based on currently accepted galaxy formation models, than have been observed. This discrepancy has been noted in
environments ranging from the field
to rich clusters, with evidence emerging that lower density regions contain
fewer dwarfs per giant than higher density regions, in further contrast
to model predictions. One possible
explanation for this involves the effects
of reionization on the forming galaxies and naturally explains both the
dearth of dwarf galaxies and the apparent environmental dependence. However,
before such theories can be fully tested, we require a better understanding
of the distribution of dwarf galaxies. Currently, there is no complete
census of the faintest dwarf galaxies in any environment.
The discovery
of the smallest and faintest dwarfs is hampered by the limitations in
detecting such faint and low surface brightness galaxies, and this is compounded
by the great difficulty in determining accurate distances to, or ascertaining
group membership for, such faint objects.
The M81 group provides a
unique means for establishing membership for galaxies in a low density region
complete to magnitudes as faint as M_R ~ -7. With
a distance modulus of
27.8, the tip of the red giant branch (TRGB) appears at I ~ 24, just
within the
reach of ground based surveys. We
currently have surveyed a 30 square degree
region around M81 with the CFHT/Megacam.
From these images we have detected
15 new candidate dwarf galaxies.
We propose to use the HST with WFPC2
to image these 15 galaxies in F606W and F814W bands in order to construct
a color-magnitude diagram down to I = 25.5 from which to measure accurate
TRGB distances to these candidate galaxies and determine star formation
and metallicity histories. The
overall project will provide a survey
of the dwarf galaxies in the M81 group environment with unprecedented completeness
to a limit of M_R < -7. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11127 Title:
Mapping
the nebula surrounding the enigmatic X-ray source at the center of the
Vela Jr
SNR PI:
Andrea
De Luca PI
Institution:
CNR,
Istituto di Astrofisica Spaziale A
compact X-ray source, showing nothing but steady unpulsed thermal
emission, lies
close to the center of the young and nearby supernova remnant dubbed "Vela
Jr". It is a typical member of a class of enigmatic sources, supposed to be
the youngest members of the radio-quiet neutron star family. Quite surprisingly,
we discovered in ground-based optical observations a small Halpha
nebula spatially coincident with the X-ray source. Such a nebula potentially
carries very important information on the nature of the X-ray source,
which remains elusive in spite of large observational efforts. We propose
to use the WFPC2 to collect high
resolution Halpha images of the nebula
in order to resolve its structure, to understand its nature, and to identify
its connection with the X-ray source. Addressing all these points will
also have important implications for our interpretation of the compact
X- ray
source and on of other objects of the same class. ====================================================================== Proposal
Category: GO Scientific
Category: UNRESOLVED STELLAR POPULATIONS ID:
11128 Title:
Time
Scales Of Bulge Formation In Nearby Galaxies PI:
David
Fisher PI
Institution:
University
of Texas at Austin Traditionally,
bulges are thought to fit well into galaxy formation models of hierarchical
merging. However, it is now becoming well established that many bulges
formed through internal, secular evolution of the disk rather than through
mergers. We call these objects pseudobulges. Much
is still unknown about
pseudobulges, the most pressing questions being:
How, exactly, do they build
up their mass? How long does it take? And, how many exist?
We are after an
answer to these questions. If pseudobulges form and evolve over longer periods
than the time between mergers, then a significant population of pseudobulges
is hard to explain within current galaxy formation theories. A pseudobulge
indicates that a galaxy has most likely not undergone a major merger
since the formation of the disk. The ages of pseudobulges give us an estimate
for the time scale of this quiescent evolution. We propose to use 21.4
orbits of HST time to complete UBVIH imaging on a sample of 33 nearby galaxies
that we have observed with Spitzer in the mid-IR. These data will be used
to measure spatially resolved stellar population parameters (mean
stellar age,
metallicity, and star formation history); comparing ages to star formation
rates allows us to accurately constrain the time scale of pseudobulge
formation. Our sample of bulges
includes both pseudo- and classical
bulges, and evenly samples barred and unbarred galaxies. Most of our sample
is imaged, 13 have complete UBVIH coverage; we merely ask to complete missing
observations so that we may construct a uniform sample for studying bulge
formation. We also wish to compare
the stellar population parameters to a
variety of bulge and global galaxy properties including star formation rates,
dynamics, internal bulge morphology, structure from bulge-disk decompositions,
and gas content. Much of this data set is already or is being assembled.
This will allow us to derive methods of pseudobulge identification that
can be used to accurately count pseudobulges in large surveys. Aside
from our
own science goals, we will present this broad set of data to the community. Thus, we waive proprietary periods for
all observations. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11129 Title:
The
Star Formation History of the Fornax Dwarf Spheroidal Galaxy PI:
Enrico
Held PI
Institution:
Osservatorio
Astronomico di Padova The
Fornax dwarf spheroidal galaxy is one of the most luminous dwarf satellites
of the Milky Way. It is unusual in
many ways:
it
hosts 5 globular clusters,
shows some relatively young stars, and has faint sub-structures which
have been interpreted as signs of recent interactions.
It is thus of great
interest to learn the complete star formation history (SFH) of Fornax to establish
a link between its evolutionary path and the predictions from numerical
simulations, as a test of our understanding of dwarf galaxy evolution.
Yet many questions remain open. Is
the old stellar population made up
of stars formed in a very early burst, perhaps before the epoch of reionisation,
or the result of a more continuous star formation between 13 and 9
Gyr ago ? How quickly did Fornax increase its metallicity during its
initial assembly
and during subsequent episodes of star formation ?
Are accretion episodes
required to explain the age-metallicity history of Fornax ? However, there
has never been a comprehensive study of the global SFH of the Fornax field
based on data of sufficient depth to unambiguously measure the age mixture
of the stellar populations and their spatial variation. We propose to use
the WFPC2 to obtain very deep images in several fields across the
central region
of Fornax in order to reach the oldest main-sequence turnoffs. The number
of fields is determined by the need to measure the SFH over different regions
with distinct kinematics and metallicity.
The resolution achievable with
HST is crucial to answer these questions because, to derive the age distribution
of the oldest stars, we are interested in I magnitude differences of
the order 0.2 mag in crowded fields at V=24.5. We
will directly measure the
time variation in star-formation rate over the entire galaxy history,
from first
stars coeval with the Milky Way halo to the youngest populations 200 Myr ago.
The combination of detailed CMD analysis with WFPC2 with our existing metallicity
and kinematic information will allow us to trace out the early phases
of its evolution. ====================================================================== Proposal
Category: GO Scientific
Category: AGN/QUASARS ID:
11130 Title:
AGNs
with Intermediate-mass Black Holes: Testing the Black Hole-Bulge
Paradigm, Part
II PI:
Luis
Ho PI
Institution:
Carnegie
Institution of Washington 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 Survey mode to obtain WFPC2 F814W images
of 85 (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. ====================================================================== Proposal
Category: GO Scientific
Category: ISM IN EXTERNAL GALAXIES ID:
11131 Title:
Star
formation at large radii in cooling flow brightest cluster galaxies PI:
Walter
Jaffe PI
Institution:
Sterrewacht
Leiden We
propose to take deep ACS FUV images of the bright central galaxies in
two powerful
cooling flow clusters for which we have VLT UBR images, with the object
of determining whether the UV excesses we observe at large radii (>15kpc)
are caused by young stars, ultrahot (WR) stars, or an as yet unknown source. Current models of excess UV light at
the AGN-dominated centers of these
galaxies cannot easily be extended to large radii.
New understanding of star
formation in these clusters will be directly applicable to scenarios of galaxy
formation in the early universe. ====================================================================== Proposal
Category: GO Scientific
Category: COOL STARS ID:
11132 Title:
Constraining
the age of the AB Dor system PI:
Markus
Janson PI
Institution:
Max-Planck-Institut
fur Astronomie, Heidelberg The
zero-age main sequence K-type star AB Dor, with an age of 25 to 125 Myr, is
the most active young star in the solar neighbourhood. It is part of a quadruple
system of young stars. The mass of AB Dor C, the
closest and lowest mass
companion, has been derived from
astrometric observations (with the VLA and
adaptive optics at the VLT) to
94+-3 times the mass of Jupiter. The low mass
(close to the hydrogen burning limit) combined with the young age makes AB
Dor C a unique calibration source for evolutionary tracks for very
low-mass stars
and brown dwarfs, provided that a precise age estimate can be derived for
the system. We propose to use the HST planetary camera to obtain
resolved component
photometry of the M-type pre-main sequence star AB Dor Ba
and Bb in order
to derive individual spectral types and luminosities, which will enable us
to age-date the AB Dor system to better than +-20 Myr. In addition, the observations
will help to constrain the Ba/Bb orbit, and hence to derive dynamical
mass estimates as well. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11133 Title:
Late-Time
Photometry of SN 2005hk: A New Kind of Type Ia Supernova PI:
Saurabh
Jha PI
Institution:
Rutgers
the State University of New Jersey Our
lack of understanding of Type Ia supernova (SN Ia) explosions limits our confidence
in their use for cosmology. While
there is broad agreement that these
objects represent the explosions of white dwarfs, the details of the explosion
mechanism are not well-understood.
Recent observations have detected
a previously unacknowledged variant class of SNe Ia whose photometric and
spectroscopic peculiarities make them quite distinct from normal SNe Ia. These
objects represent a challenge for thermonuclear supernova models, as a complete
theory of exploding white dwarfs must allow for their existence. A particularly
well-studied example of this class of objects is the recent SN 2005hk,
whose properties in some respects resemble those of models which invoke
a subsonic burning front, called a deflagration. We
propose to test SN Ia
models by obtaining late-time photometry for this extreme SN Ia using
WFPC2 and
NICMOS on HST. We will accurately
measure the late-time photometric decline
rate and spectral energy distribution (SED). These
observations will allow
us to test whether the ejecta contain the large amount of oxygen predicted
by certain models, the efficiency of energy deposition by gamma rays and
positrons, and possibly detect major evolution of the SED expected due
to a
change in the dominant cooling mechanism of the ejecta. ====================================================================== Proposal
Category: GO Scientific
Category: UNRESOLVED STELLAR POPULATIONS ID:
11134 Title:
WFPC2
Tidal Tail Survey: Probing Star
Cluster Formation on the Edge PI:
Karen
Knierman PI
Institution:
University
of Arizona The
spectacular HST images of the interiors of merging galaxies such as the Antennae
and NGC 7252 have revealed rich and diverse populations of star clusters
created over the course of the interaction. Intriguingly,
our WFPC2 study
of tidal tails in these and other interacting pairs has shown that star cluster
birth in the tails does not follow a similarly straightforward evolution. In fact, cluster formation in these
relatively sparse environments is
not guaranteed -- only one of six tails in our initial study showed evidence
for a significant population of young star clusters.
The tail environment
thus offers the opportunity to probe star cluster formation on the edge
of the physical parameter space (e.g., of stellar and gas mass, density, and
pressure) that permits it to occur.
We propose to signficantly extend our pilot
sample of optically bright, gas-rich tidal tails by a factor of 4 in number
to include a more diverse population of tails, encompassing major and minor
mergers, gas-rich and gas-poor tails, as well as early, late, and merged interaction
stages. With 21 orbits of HST WFPC2 imaging in the F606W and F814W filters,
we can identify, roughly age-date, and measure sizes of star clusters to
determine what physical parameters affect star cluster formation. WFPC2 imaging
has been used effectively in our initial study of four mergers, and it will
be possible in this program to reach similar limits of Mv=-8.5 for each of
16 more tails. With the much
larger sample we expect to isolate which factors,
such as merger stage, HI content, and merger mass ratio, drive the formation
of star clusters. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11135 Title:
Extreme
makeovers: Tracing the transformation of massive galaxies at z~2.5 PI:
Mariska
Kriek PI
Institution:
Universiteit
Leiden To
obtain a full spectroscopic census of the universe at z~2.5 we have conducted
a near-infrared spectroscopic survey for K-selected galaxies. We found
that, in contrast to the local universe, massive high-redshift galaxies span
a wide range of properties, varying from (dusty) star burst to "red and dead"
galaxies. This may imply that massive galaxies transform from star- forming
to quiescent galaxies in the targeted redshift range. To understand whether
the 9 quiescent galaxies in our sample are the progenitors of local elliptical,
we are observing them in the current cycle with NIC2.
For cycle 16
we propose to complete our sample of massive z~2.5 galaxies and image
the remaining
10 galaxies, which all have emission lines. Based on emission-line diagnostics,
6 of these galaxies are identified as star-forming objects and 4 harbor
an active galactic nucleus. The goals are to 1) determine whether star formation
in massive z~2.5 galaxies takes place in disks or is triggered by merger
activity, 2) derive the contribution of AGNs to the rest-frame optical emission,
and 3) test whether the morphologies are consistent with the idea that
the star-forming galaxies, AGNs, and quiescent galaxies represent subsequent
phases of an evolutionary sequence. The combination of both programs
will provide the first morphological study of a spectroscopically confirmed
massive galaxy sample at z~2.5. ====================================================================== Proposal
Category: GO Scientific
Category: COOL STARS ID:
11136 Title:
Resolving
Ultracool Astrophysics with Brown Dwarf Binaries PI:
Michael
Liu PI
Institution:
University
of Hawaii We
propose to obtain resolved far-red and near-IR photometry of 14 brown
dwarf binaries
with HST/NICMOS in order to study one of the long-standing puzzles in ultracool
astrophysics, namely the rapid change in spectra from L dwarfs to T dwarfs
at nearly constant effective temperature (a.k.a. the ``L/T transition''). While many nearby brown dwarfs have
been studied, use of such samples
is inevitably hindered by the unknown ages, masses, and metallicities of
the field population.
Characterization of resolved ultracool binaries is a promising
avenue for addressing this problem, by providing coeval systems of the
same composition with comparable masses and temperatures.
Our proposed HST/NICMOS
(0.9-1.6 micron) observations will be combined with longer wavelength
ground-based photometry and spectroscopy from Keck laser guide star adaptive
optics. The resulting multi-band
(0.9-2.5 micron) dataset will be a unique
resource for measuring the evolution of spectral energy distributions across
the L/T transition, to test state-of-the-art atmospheric models, and to determine
the physical process(es) that dominate the L/T transition. Understanding
the L/T transition is important not only for testing brown dwarf atmospheres,
but also provides a key pathway for understanding the same physical
effects, namely the formation and removal of clouds, in the atmospheres
of the extrasolar planets. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11137 Title:
First
Accurate Geometric Distance to a Galactic Wolf-Rayet Star: Knots in the
Ejecta
M1-67 PI:
Anthony
Moffat PI
Institution:
Universite
de Montreal M
1-67 is the youngest known ejection nebula surrounding a Population I
Wolf- Rayet
star, in this case the WN8 star WR 124.
Our deep H-alpha HST/WFPC2 image
of this object in March 1997 revealed, for the first time in such a nebula,
numerous bright, mostly unresolved knots (typical diameters 0.1-0.2") often
surrounded by what appear to be their own local spherical diffuse 'wind' bubbles.
We propose to obtain a second epoch H-alpha image of M 1-67, essentially
repeating the Epoch1 instrumental set-up. By measuring the proper motions
of the knots, we will derive a
relatively precise and assumption-free geometric
distance (thus also a luminosity)
to a Galactic Wolf-Rayet
star, the
first of its kind. This will help to confirm the suspected runaway
status of
WR 124 and shed new light on the nature of progenitors of
gamma-ray bursts.
Moreover, we intend to document and measure the anticipated morphology/brightness
changes in the fine-stucture features of the nebula over the
11-year interval, as they relate to wind-embedded shocks. This will provide
important input for interaction models of a stellar wind with circumstellar
matter. ====================================================================== Proposal
Category: GO Scientific
Category: AGN/QUASARS ID:
11138 Title:
The
Physics of the Jets of Powerful Radio Galaxies and Quasars PI:
Eric
Perlman PI
Institution:
Florida
Institute of Technology We
propose to obtain HST polarimetry of the jets of the quasars 1150+497
and PKS
1136-135. Our goal is to solve the
riddle of their high-energy emission mechanism,
and tackle issues such as particle acceleration and jet dynamics. Our
targets are the optically brightest quasar jets, and they span the range of
luminosities and beaming parameters seen in these objects.
Recent observations
with Spitzer, HST and Chandra have shed new light on the spectral morphology
of quasar jets, throwing wide open the question of the nature of their
optical and X-ray emission. Three
mechanisms are possible, including synchrotron
emission as well as two Comptonization processes. Polarimetry
can uniquely
determine which of these mechanisms operates in the optical. We will compare
the optical polarimetry to in-hand radio polarimetry as well as in- hand
and new Spitzer, HST and Chandra imaging to gain new insights on the structure
of these jets, as well as particle acceleration mechanisms and jet dynamics. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11139 Title:
NICMOS
Observations of the Microquasar GRS 1758-258 PI:
Ian
Smith PI
Institution:
Rice
University The
galactic black hole candidate GRS 1758-258 is normally one of the brightest
persistent gamma-ray sources in the vicinity of the galactic center. It
is a microquasar with relativistic radio jets emanating from a central variable
source. Microquasars are excellent
nearby test laboratories for studying
the complex accretion and outflow processes that take place near black
hole horizons. Despite an accurate
location provided by Chandra and the VLA
and over a decade of careful ground-based studies, the optical/infrared counterpart
to GRS 1758-258 remains unknown. A stellar counterpart is expected,
but the current candidates are all more than 2 sigma from the center of
the error circle. The ground-based
infrared flux limits are also right at the
values expected for the synchrotron emission from the outflow from the black
hole, and possibly for the emission from the accretion disk. This leaves open
the question as to what is powering this very energetic persistent source. Here we propose to use NICMOS to
perform broad-band imaging of the GRS
1758-258 error box. These images
will be more than three magnitudes more sensitive
than the current ground-based ones. The resulting spectra will reveal
the thermal/non-thermal nature of the sources in the region of the error
box, and the high spatial resolution images may reveal a jet structure. We
propose to perform three visits of two orbits each spanning the
suggested 18.45
day binary orbital period of the system: a
correct counterpart identification
should be confirmed by its variability.
We will also aim to support
the HST observations with X- and gamma-ray observations using Swift or INTEGRAL,
and with longer wavelength observations from the ground. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11140 Title:
Can
mass-ejections from late He-shell flash stars constrain
convective/reactive
flow modeling of stellar interiors? PI:
Klaus
Werner PI
Institution:
Universitat
Tubingen, Institut fur Astronomie & Astrophysik The
existence of H-deficient knots around the central stars of the planetary nebulae
Abell 30 and Abell 78 is still unexplained. We hypothesize that these knots
were ejected during a very late helium-shell flash (= very late thermal pulse,
VLTP) suffered by the precursor white dwarf stars. If this is true, then
the characteristics of these knots (mass, velocity, density, spatial distribution)
allow to draw conclusions on the course of the hydrogen- ingestion
flash detonation that is triggered by the He-shell flash. This provides
important, otherwise inaccessible constraints for the hydrodynamical modeling
of convective/reactive flows in stellar interiors. Understanding the physics
of these flows is not only important for the understanding of these particular
central stars, but also for the frequent, very similar convective/reactive
events that determine the nucleosynthesis in Pop. III stars. With this proposal we want to proof or
discard the idea that the H- deficient
knots are resulting from a VLTP. If true, then they can be exploited for
flash-physics diagnostics. We propose a simple test. We search for such knots
around five H-deficient central stars (PG1159 stars). Our models predict,
that only those stars with residual nitrogen in the atmosphere have suffered
a VLTP and, hence, should have expelled knots. We therefore want to take
[O III] images of stars which have photospheric N and those which do
not. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11141 Title:
White
dwarfs in the open star cluster NGC 188 PI:
Kurtis
Williams PI
Institution:
University
of Texas at Austin White
dwarf cooling sequences represent the only ways in which we can determine
ages of Galactic components such as the disk and the halo, and they are
an independent check on main sequence ages of globular
star clusters. These
age measurements rely heavily on theoretical cooling models, many of which
disagree by as much as a few gigayears for the coolest white dwarfs. Further,
observations of the white dwarf sequence in the super metal-rich open cluster
NGC 6791 have found a white dwarf age several gigayears younger than the
accepted cluster age determined by main-sequence fitting.
The white dwarf sequence
of the solar-metallicity, 7-Gyr old open cluster NGC 188 can provide some
much-needed insight into these uncertainties, but previous HST observations
were too shallow to detect the oldest, faintest white dwarfs in the
cluster. We propose deep imaging
of two fields at the center of the cluster
with the following goals: (1)
To detect the end of the white dwarf cooling
sequence, providing a much-needed empirical data point for cool white dwarf
evolutionary models, (2) to compare the white dwarf luminosity function of
NGC 188 with that of NGC 6791 to determine if the odd white dwarf
sequence in
the latter cluster is due to the cluster's high metallicity or due to a shortcoming
in theoretical models, and (3) to determine via photometry the masses
of white dwarfs formed by solar-mass stars, a quantity not yet empirically
measured. ====================================================================== Proposal
Category: GO Scientific
Category: ISM IN EXTERNAL GALAXIES ID:
11142 Title:
Revealing
the Physical Nature of Infrared Luminous Galaxies at 0.3<z<2.7
Using HST
and Spitzer PI:
Lin
Yan PI
Institution:
California
Institute of Technology We
aim to determine physical properties of IR luminous galaxies at
0.3<z<2.7 by
requesting coordinated HST/NIC2 and MIPS 70um observations of a unique, 24um
flux-limited sample with complete Spitzer mid-IR spectroscopy. The 150 sources
investigated in this program have S(24um) > 0.8mJy and their mid-IR spectra
have already provided the majority targets with spectroscopic redshifts
(0.3<z<2.7). The proposed 150~orbits of NIC2 and 66~hours of MIPS 70um
will provide the physical measurements of the light distribution at the rest-frame
~8000A and better estimates of the bolometric luminosity. Combining these
parameters together with the rich suite of spectral diagnostics from the mid-IR
spectra, we will (1) measure how common mergers are among LIRGs and ULIRGs
at 0.3<z<2.7, and establish if major mergers are the drivers of
z>1 ULIRGs,
as in the local Universe. (2) study the co-evolution of star formation and
blackhole accretion by investigating the relations between the fraction
of starburst/AGN
measured from mid-IR spectra vs. HST morphologies, L(bol) and z. (3)
obtain the current best estimates of the far-IR emission, thus L(bol)
for this
sample, and establish if the relative contribtuion of mid-to-far IR dust emission
is correlated with morphology (resolved vs. unresolved). ====================================================================== Proposal
Category: GO Scientific
Category: UNRESOLVED STELLAR POPULATIONS ID:
11143 Title:
NICMOS
imaging of submillimeter galaxies with CO and PAH redshifts PI:
Andrew
Baker PI
Institution:
Rutgers
the State University of New Jersey We
propose to obtain F110W and F160W imaging of 10 z~2.4 submillimeter galaxies
(SMGs) whose optical redshifts have been confirmed by the detection of
millimeter CO and/or mid-infrared PAH emission. With
the 4000A break falling
within/between the two imaging filters, we will be able to study these sources'
spatially resolved stellar populations (modulo extinction) in the rest-frame
optical. SMGs' large luminosities
appear to be due largely to merger-triggered
starbursts; high-resolution NICMOS imaging will help us understand
the stellar masses, mass ratios, and other properties of the merger progenitors,
valuable information in the effort to model the mass assembly history
of the universe. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11144 Title:
Building
on the Significant NICMOS Investment in GOODS: A Bright, Wide-Area
Search for
z>=7 Galaxies PI:
Rychard
Bouwens PI
Institution:
University
of California - Santa Cruz One
of the most exciting frontiers in observational cosmology has been to trace
the buildup and evolution of galaxies from very early times. While hierarchical
theory teaches us that star formation in galaxies likely starts out
small and builds up gradually, only recently has it been possible to see evidence
for this observationally through the evolution of the LF from z~6 to z~3. Establishing that this build up occurs
from even earlier times (z~7-8) has
been difficult, however, due to the small size of current high-redshift z~7-8
samples -- now numbering in the range of
~4-10 sources. Expanding
the size
of these samples is paramount, if we are to push current studies of galaxy
buildup back to even earlier times.
Fortunately, we should soon be able
to do so, thanks to ~50 arcmin**2 of deep (26.9 AB mag at 5 sigma)
NICMOS 1.6
micron data that will be available over the two ACS GOODS fields as a result
of one recent 180-orbit ACS backup program and a smaller program. These
data will nearly triple the deep near-IR imaging currently available over
these fields and therefore represent a significant resource for finding and
characterizing the brightest and likely most massive high-redshift
sources (which
can be found in no other way but with wide-area searches).
To make maximal
use of these data, we will first isolate a small sample of the most interesting,
candidate z>=7 galaxies from this survey through their z-H colours. We then propose to follow-up each
of these candidates with NICMOS imaging
at 1.1 microns ('J'-band) to determine which of these sources are at z>=7
and thus significantly expand our sample of luminous, z>=7 galaxies. Since
preliminary studies indicate that these candidates occur in only 30% of the
NIC3 fields, our follow-up strategy is ~3 times as efficient as without this
preselection and 9 times as efficient as a search in a field with no
pre- existing
data. We expect to identify ~8
luminous z-dropouts and possibly ~2 z~10
J-dropouts as a result of this program, more than tripling the number currently
known. The increased sample sizes
are important if we are to solidify
current conclusions about galaxy buildup and the evolution of the LF from
z~8. In addition to the high
redshift science, these deep 1.1 micron data
would have significant value for many diverse endeavors, including (1) improving
our constraints on the stellar mass density at z~7-10 and (2) doubling
the number of galaxies at z~6 for which we can estimate dust obscuration. ====================================================================== Proposal
Category: GO Scientific
Category: STAR FORMATION ID:
11145 Title:
Probing
the Planet Forming Region of T Tauri Stars in Chamaeleon PI:
Nuria
Calvet PI
Institution:
University
of Michigan By
studying the inner, planet-forming regions of circumstellar disks around low-mass
pre-main sequence stars we can refine theories of giant planet formation
and develop timescales for the evolution of disks and their planets. Spitzer
infrared observations of T Tauri stars in the Chamaeleon star-forming region
have given us an unprecedented look at dust evolution in young objects. However,
despite this ground breaking progress in studying the dust in young disks,
the gas properties of the inner disk remain essentially unknown. Using ACS
on HST, we propose to measure the H_2
emission originating in the innermost
disk regions of classical T Tauri stars in different stages of evolution
with the objective of revealing the timescales of gas dissipation and
its relationship to dust evolution.
This proposal is part of a comprehensive
effort with approved programs on Spitzer, Gemini, and Magellan that
aim to characterize the state of gas and dust in disks where planets may already
have formed. ====================================================================== Proposal
Category: GO Scientific
Category: ISM IN EXTERNAL GALAXIES ID:
11146 Title:
The
Role of Stellar Feedback in Galaxy Evolution PI:
Daniela
Calzetti PI
Institution:
University
of Massachusetts Stellar
feedback - the return of mass and energy from star formation to the interstellar
medium - is one of the primary engines of galaxy evolution. Yet, the
observational canvass of feedback is incomplete. We propose to
investigate this
fundamental aspect of star formation on one local actively star-forming galaxy,
He2-10, selected to occupy an
unexplored niche in the key parameter space
of stellar mass. The WFPC2
narrow-band observations in the light of H- beta,
[OIII], H-alpha, and [SII] will: (1)
discriminate the feedback-induced shock
fronts from the photoionized regions; (2) map, and provide a complete census
of, the shocks inside and around the starburst regions; and (3) measure the
energy budget of the star-formation-produced shocks. These observations, joined
by our previous data and studies on starbursts, will yield: (1) the efficiency
of the feedback, i.e. the fraction of the star formation's mechanical
energy transported out of the starburst volume rather than radiated away,
in the dual-parameter space of host's stellar mass and star formation intensity;
(2) the conditions under which feedback morphs from a localized process
to a galactic scale mechanism. The high angular resolution of HST is crucial
for separating the spatially narrow shock fronts (~10 pc=0.2" at 10 Mpc)
from the more extended photoionization fronts. This project will provide the
most comprehensive quantitative foundation of stellar feedback and a
gauge for
determining the role of feedback in the energetics, structure and star formation
history of galaxies. ====================================================================== Proposal
Category: GO Scientific
Category: UNRESOLVED STELLAR POPULATIONS ID:
11147 Title:
The
Origin of Diffuse UV Light from Spiral Disks PI:
Rupali
Chandar PI
Institution:
Carnegie
Institution of Washington The
ultraviolet light from galaxies has been used as a beacon for tracing
the cosmic
star formation history of the Universe, yet we have an incomplete understandingof
many characteristics of this light.
Most of the UV emission from
nearby, normal star--forming galaxies is unresolved and "diffuse",
and GALEX
has shown that in spiral disks it permeates the inter-arm regions. The nature
of this diffuse inter-arm component is under debate.
Recent results suggest
that it may arise from non-ionizing UV photons which originate in star forming
regions in the spiral arms, travel in the plane of the galaxy, and then
scatter off of diffusely distributed cold dust grains.
Alternatively, an in-situ,
unresolved stellar population could produce the observed inter-arm UV emission. This project seeks to establish which
of the two competing scenarios
is responsible for the bulk of this diffuse emission.
We propose to use
HST's UV imaging capability (ACS/SBC) to obtain deep observations of selected
fields in the nearby spiral galaxy M101, for which available (low angular
resolution) data favor the 'scattered light' scenario.
Our observations
are designed to detect any faint, UV-luminous stellar population down
to main sequence B5 stars. With
these data, we will establish the nature of
the bulk of the diffuse UV light in this spiral galaxy by:
(i)
quantifying the
contribution from dust-scattered light; (ii) measuring the contribution
to the
ubiquitous diffuse ionized medium from in-situ ionizing stars; and (iii) providing
constraints on the observed stellar mass function in the field. Only
HST has the UV sensitivity and angular resolution to discriminate
in-situ stellar
populations from scattered light.
The ultimate goal of this project is
to re-'calibrate' the UV emission as a star formation rate indicator,
which will
need to account for any scattered component. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11148 Title:
High
Contrast Imaging of Dusty White Dwarfs PI:
John
Debes PI
Institution:
Carnegie
Institution of Washington For
the past 18 years, only one white dwarf with a circumstellar dust disk
was known
to exist. In the last two years,
six new disks have been discovered. Since
all material inwards of a few AU should be scoured clean during post main
sequence evolution, the primary explanation is the presence of a planetary
system that is perturbing relic planetesimals into the tidal disruption
radius of the white dwarf. Dusty
disks around white dwarfs should be
markers for planets and we propose to use high contrast imaging to
search for
faint companions down to 6 M_$J$ that may be feeding the disks. White dwarfs
are uniquely suited for planet searches, where the planet/white dwarf contrast
is less than for main sequence stars. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11149 Title:
Characterizing
the Stellar Populations in Lyman-Alpha Emitters and Lyman Break
Galaxies at
5.7<z<7 in the Subaru Deep Field PI:
Eiichi
Egami PI
Institution:
University
of Arizona The
epoch of reionization marks a major phase transition of the Universe, during
which the intergalactic space became transparent to UV photons. Determining
when this occurred and the physical processes involved represents the
latest frontier in observational cosmology. Over the last few years, searches
have intensified to identify the population of high-redshift (z>6) galaxies
that might be responsible for this process, but the progress is hampered
partly by the difficulty of obtaining physical information (stellar mass,
age, star formation rate/history) for individual sources. This is because
the number of z>6 galaxies that have both secure spectroscopic redshifts
and high-quality infrared photometry (especially with Spitzer/IRAC) is
still fairly small. Considering that only several photometric points are available
per source, and that many model SEDs are highly degenerate, it is crucial
to obtain as many observational constraints as possible for each source
to ensure the validity of SED modeling. To better understand the physical
properties of high-redshift galaxies, we propose here to conduct HST/NICMOS
(72 orbits) and Spitzer/IRAC (102 hours) imaging of spectroscopically
confirmed, bright (z<26 mag (AB)) Ly-alpha emitters (LAEs) and
Lyman-break galaxies (LBGs) at 5.7<z<7 selected from the Subaru
Deep Field.
Spectroscopic redshifts remove one critical free parameter from SED modeling
while bright source magnitudes ensure high-quality photometric data. By
making accurate determinations of stellar masses, ages, and
star-formation histories,
we will specifically address the following major questions: (1)
Do LAEs
and LBGs represent physically different galaxy populations at z>6 as suggested
recently? (2) Is Ly-alpha emission systematically suppressed at z>6 with
respect to continuum emission? (i.e., are we reaching the epoch of incomplete
reionization?), and (3) Do we see any sign of abnormally young stellar
population in any of the z>6 galaxies? ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11150 Title:
Beta
Pic Polarimetry with NICMOS PI:
James
Graham PI
Institution:
University
of California - Berkeley Debris
disk stars host transient dust grains that comprise a collisional cascade
with sizes ranging from planetesimals to the sub-micron. In addition to
the gravity of the host star and any planets present, these grains are subject
to size-dependent non-gravitational forces, e.g., corpuscular drag and radiation
pressure. When a steep spectrum of grain sizes prevails, such as the Dohnanyi
distribution, scattered light images preferentially trace grains with dimensionless
size parameter of order unity. Thus images in scattered starlight
provide unique windows on the balance of forces acting on grains at a
specific size. Therefore, in an A star system such as beta Pic, the
near-IR is
dominated by grains close to the blow out size and therefore NICMOS
traces dust
on hyperbolic orbits. Scattering
is fundamentally polarization sensitive,
and measurements that record intensity literally see only half the picture.
If linear polarization is measured then the elements of the complex scattering
matrix can be reconstructed. These matrix elements provide fundamental
constraints on the size, composition and structure of the scatterers.
Notably, polarimetry can be used to break the degeneracy between scattering
asymmetry, g, and the radial dust gradient, which are otherwise covariant
in an edge-on disk. Thus, we can use polarimetry to localize the parent
bodies in the beta Pic disk. In
beta Pic, dust is thought to originate mainly
from the sublimation of cometary bodies near periastron. The irradiation
of cometary material leads to sublimation and photodissociation of ices
forming porous grains consisting of a matrix of refractory material.
Such grains
have a characteristic scattering signature in polarized light that can be
distinguished from compact grains that arise from collisional erosion of asteroidal
material. ====================================================================== Proposal
Category: GO Scientific
Category: STAR FORMATION ID:
11151 Title:
Evaluating
the Role of Photoevaporation of Protoplanetary Disk Dispersal PI:
Gregory
Herczeg PI
Institution:
California
Institute of Technology Emission
produced by accretion onto the central star leads to photoevaporation,
which may play a fundamental role in disk dispersal.
Models of
disk photoevaporation by the central star are challenged by two
potential problems: the emission
produced by accretion will be substantially weaker for low-mass
stars, and photoevaporation must continue as accretion slows. Existing
FUV spectra of CTTSs are biased to solar-mass stars with high accretion
rates, and are therefore insufficient to address these problems. We propose
use HST/ACS SBC PR130L to obtain FUV spectra of WTTSs and of CTTSs at low
masses and mass accretion rates to provide crucial data to evaluate photoevaporation
models. We will estimate the FUV
and EUV luminosities of low-mass
CTTSs with small mass accretion rates, CTTSs with transition disks and
slowed accretion, and of magnetically-active WTTSs. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11152 Title:
Probing
the compact dust disk of a nearby Classical T Tauri Star PI:
Bruce
Macintosh PI
Institution:
Lawrence
Livermore National Laboratory BP
Psc is a high Galactic latitude (b = -57), bright, IRAS source that generally
has been classified as a T Tauri star but little studied to date. We have
carried out a multiwavelength ground-based study of this object and find that
it is most likely a ~10 Myr classical T Tauri star surrounded by a gas and
dust disk, and less than 100 pc from Earth, making it one of the oldest and
closest such stars known. Near-IR AO images and IR photometry show it is surrounded
by an compact (0.2"), almost-edge-on, optically
thick disk of dust with
a wide range of temperatures. We propose a multiwavelength polarimetric study
of the compact disk to support quantitative modeling to recover disk and dust
parameters. We also propose coronagraphic imaging to search for larger- scale
dust structures invisible in ground-based images, and narrowband imaging of
an outflow jet and associated Herbig-Haro objects to study their
structure and
determine a kinematic distance of the system. A massive compact disk surrounding
an isolated 10 Myr star is a unique environment for planet formation,
and its proximity to Earth allows HST to study it in detail. ====================================================================== Proposal
Category: GO Scientific
Category: UNRESOLVED STELLAR POPULATIONS ID:
11153 Title:
The
Physical Nature and Age of Lyman Alpha Galaxies PI:
Sangeeta
Malhotra PI
Institution:
Arizona
State University In
the simplest scenario, strong Lyman alpha emission from high redshift galaxies
would indicate that stellar populations younger than 10 Myrs dominate the
UV. This does not, however, constrain the stellar populations older than 100
Myrs, which do not contribute to UV light. Also,
the Lyman alpha line can be
boosted if the interstellar medium is both clumpy and dusty. Different studies
with small samples have reached different conclusions about the presence
of dust and old stellar populations in Lyman alpha emitters. We propose
HST-NICMOS and Spitzer-IRAC photometry of
35 Lyman-alpha galaxies at redshift
4.5<z<6.5, in order to determine their spectral energy
distribution (SED)
extending through rest-frame optical. This will allow us to measure accurately
(1) The total stellar mass in these objects, including old stars which
may have formed at redshifts (z > 8) not easily probed by any other means. (2) The dust extinction in the
rest-frame UV, and therefore a correction
to their present star-formation rates.
Taken together, these two quantities
will yield the star-formation histories of Lyman alpha galaxies, which
form fully half of the known galaxies at z=4-6. They will tell us whether
these are young or old galaxies by straddling the 4000A break. Data from
NICMOS is essential for these compact and faint (i=25-26th magnitude AB) high
redshift galaxies, which are too faint for good near-IR photometry from the
ground. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11154 Title:
Optical-UV
Spectrum of the Middle-aged Pulsar B1055-52 PI:
George
Pavlov PI
Institution:
The
Pennsylvania State University The
middle-aged radio, X-ray and gamma-ray pulsar B1055-52 is one of the few pulsars
that allow a multiwavelength study of pulsar radiation. An optical counterpart
of the pulsar has been detected with the HST FOC, but it was observed
in only one filter (F342W, m=24.9). To understand the nature of the pulsar
radiation, its spectrum must be measured in a broad wavelegth range. We propose
imaging observations of the pulsar's counterpart with
WFPC2 in the red
part of the spectrum and ACS/SBC in the UV part to measure the broadband spectral
distribution, compare it with the X-ray spectrum, and investigate the thermal
and magnetospheric components of the pulsar's radiation. ====================================================================== Proposal
Category: GO Scientific
Category: STAR FORMATION ID:
11155 Title:
Dust
Grain Evolution in Herbig Ae Stars:
NICMOS
Coronagraphic Imaging and Polarimetry PI:
Marshall
Perrin PI
Institution:
University
of California - Berkeley We
propose to take advantage of the sensitive coronagraphic capabilities of NICMOS
to obtain multiwavelength coronagraphic imaging and polarimetry of primordial
dust disks around young intermediate-mass stars (Herbig Ae stars), in
order to advance our understanding of how dust grains are assembled into larger
bodies. Because the polarization
of scattered light is strongly dependent
on scattering particle size and composition, coronagraphic imaging polarimetry
with NICMOS provides a uniquely powerful tool for measuring grain properties
in spatially resolved circumstellar disks. It
is widely believed that
planets form via the gradual accretion of planetesimals in gas-rich, dusty
circumstellar disks, but the connection between this suspected process and
the circumstellar disks that we can now observe around other stars
remains very
uncertain. Our proposed
observations, together with powerful 3-D radiative
transfer codes, will enable us to quantitatively determine dust grain
properties as a function of location within disks, and thus to test whether
dust grains around young stars are in fact growing in size during the putative
planet-formation epoch. HST
imaging polarimetry of Herbig Ae stars will
complement and extend existing polarimetric studies of disks around lower-mass
T Tauri stars and debris disks around older main-sequence stars. When
combined with these previous studies, the proposed research will help us establish
the influence of stellar mass on the growth of dust grains into larger
planetesimals, and ultimately to planets.
Our results will also let us calibrate
models of the thermal emission from these disks, a critical need for validating
the properties of more distant disks inferred on the basis of spectral
information alone. ====================================================================== Proposal
Category: SNAP Scientific
Category: SOLAR SYSTEM ID:
11156 Title:
Monitoring
Active Atmospheres on Uranus and Neptune PI:
Kathy
Rages PI
Institution:
SETI
Institute We
propose Snapshot observations of Uranus and Neptune to monitor changes
in their
atmospheres on time scales of weeks and months. Uranus
equinox is only months
away, in December 2007. Hubble
Space Telescope observations during the past
several years (Hammel et al. 2005, Icarus 175, 284 and references therein)
have revealed strongly wavelength-dependent latitudinal structure, the
presence of numerous visible-wavelength cloud features in the northern hemisphere,
at least one very long-lived discrete cloud in the southern hemisphere,
and in 2006 the first dark spot ever seen on Uranus.
Long-term ground-based
observations (Lockwood and Jerzekiewicz, 2006, Icarus 180, 442; Hammel
and Lockwood 2007, Icarus 186, 291) reveal seasonal brightness changes whose
origins are not well understood. Recent near-IR images of Neptune obtained
using adaptive optics on the Keck Telescope, together with HST observations
(Sromovsky et al. 2003, Icarus 163, 256 and references therein) which
include previous Snapshot programs (GO 8634, 10170, 10534) show a general
increase in activity at south temperate latitudes until 2004, when Neptune
returned to a rather Voyager-like appearance. Further
Snapshot observations
of these two dynamic planets will elucidate the nature of long- term
changes in their zonal atmospheric bands and clarify the processes of formation,
evolution, and dissipation of discrete albedo features. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11157 Title:
NICMOS
Imaging Survey of Dusty Debris Around Nearby Stars Across the Stellar
Mass
Spectrum PI:
Joseph
Rhee PI
Institution:
University
of California - Los Angeles Association
of planetary systems with dusty debris disks is now quite secure, and
advances in our understanding of planet formation and evolution can be achieved
by the identification and characterization of an ensemble of debris disks
orbiting a range of central stars with different masses and ages. Imaging
debris disks in starlight scattered by dust grains remains technically challenging
so that only about a dozen systems have thus far been imaged. A further
advance in this field needs an increased number of imaged debris disks. However, the technical challege of such
observations, even with the superb
combination of HST and NICMOS, requires the best targets.
Recent HST imaging
investigations of debris disks were sample-limited not limited by the technology
used. We performed a search for
debris disks from a IRAS/Hipparcos cross
correlation which involved an exhaustive background contamination check to
weed out false excess stars. Out
of ~140 identified debris disks, we selected
22 best targets in terms of dust optical depth and disk angular size. Our
target sample represents the best currently available target set in
terms of
both disk brightness and resolvability.
For example, our targets have higher
dust optical depth, in general, than newly identified Spitzer disks. Also,
our targets cover a wider range of central star ages and masses than previous
debris disk surveys. This will help us to investigate planetary system
formation and evolution across the stellar mass spectrum.
The technical
feasibility of this program in two-gyro mode guiding has been proven with
on-orbit calibration and science observations during HST cycles 13, 14, and
15. ====================================================================== Proposal
Category: GO Scientific
Category: UNRESOLVED STELLAR POPULATIONS ID:
11158 Title:
HST
Imaging of UV emission in Quiescent Early-type Galaxies PI:
R.
Rich PI
Institution:
University
of California - Los Angeles 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 responsbile
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. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11159 Title:
The
True Galactic Bulge Luminosity Function PI:
R.
Rich PI
Institution:
University
of California - Los Angeles We
propose to obtain second epoch imaging of the deep Galactic bulge field observed
using NICMOS by Zoccali et al. (2000).
The bulge luminosity and mass function
suffered from 30-50% contamination by foreground disk stars, which was
impossible to correct for in the original study. Revisiting
the field after
9 years, we propose to segregate the foregound disk stars because they have
large transverse velocities, thus revealing the luminosity function of Galactic
bulge low mass stars to near the hydrogen burning limit.
The slope of
the mass function has implications for galaxy formation and for understanding
the nature of microlensing in the Galactic bulge. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11160 Title:
Escape
fraction and stellar populations in a highly magnified Lyman-Break
Galaxy PI:
Johan
Richard PI
Institution:
California
Institute of Technology Understanding
how star-forming galaxies contribute to cosmic reionization is one
of the frontiers of observational cosmology. A key ingredient in this issue
is measuring the escape fraction of Lyman-continuum photons in high redshift
galaxies (z>3). Gravitationally lensed Lyman-break galaxies (LBGs) act
as important laboratories for studying the resolved physical properties
at sub-kpc
scales with high signal-to-noise. Correlating the local escape fraction
with physical parameters derived from stellar population modeling (such
as the star formation rate, age and reddening) will offer new insights into
understanding the physical processes involved with the production of ionizing
photons. We propose here follow-up
observations of the "Cosmic Eye", a
remarkable, highly magnified (x 30), Lyman-break galaxy at z~3.07 using WFPC2
and NICMOS. Deep ultraviolet WFPC2 imaging will provide a detailed study of
variations in the escape fraction, while WFPC2 and NICMOS/NIC2 imaging
will complement
the current broad-band detections to allow a precise modeling of the
spatially-dependent spectral energy distribution. This will allow the first
comprehensive analysis between the escape fraction, the local SED and the
dynamics of a distant galaxy. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11161 Title:
Revealing
the Explosion Geometry of Nearby GRB-SNe PI:
Alicia
Soderberg PI
Institution:
California
Institute of Technology The
connection between gamma-ray bursts and Type Ibc supernovae is well- established
in broad terms. However, our
recent identification of an intermediate
class of sub-energetic GRBs, and the overall overlap in Nickel production
between GRB-SNe and ordinary SNe Ibc suggest that the properties leading
to the production of a relativistic engine are yet to be uncovered. A fundamental
difference between the two classes of explosions may be imprinted in
the overall geometry of the explosion. The relativistic component of
GRBs is
known to be highly collimated, but it is unclear if the SN blast is spherical
or mildly collimated as well. Here we propose HST observations of the
late (>30 days) decay tails of two GRB-SNe as an independent measure
of the
Nickel mass synthesized in the explosion.
A comparison to the Nickel mass inferred
from the peak brightness of the SNe will provide a direct measure of the
explosion asymmetry, since at late time the explosion is essentially spherical.
These observations will form the core of a multi-wavelength (optical,
X-ray, radio) effort to fully characterize all aspects of the explosions,
from the energy and geometry of the relativistic material (VLA, Chandra)
to the early SN evolution (Keck, Magellan). The
proposed observations
require two slow-response (>30 days) TOOs, ideally suited to the 2-gyro
operations of HST. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11162 Title:
Understanding
the Long Term Impacts of Low Magnetic Accretion PI:
Paula
Szkody PI
Institution:
University
of Washington The
low accretion rate Polar EF Eri has been in a low state for more than 9 years.
Our recent GALEX photometry revealed a source of UV light that is producing
more flux than the white dwarf and which is highly modulated on the 81
min orbital period of the system. We request UV spectra with the SBC on
the ACS
to resolve whether limb darkening or cyclotron emission can explain the observed
phenomena and provide insight on the long term heating effects under low
accretion scenarios. ====================================================================== Proposal
Category: GO Scientific
Category: HOT STARS ID:
11163 Title:
Accreting
Pulsating White Dwarfs in Cataclysmic Variables PI:
Paula
Szkody PI
Institution:
University
of Washington Recent
ground-based observations have increased the number of known pulsating white
dwarfs in close binaries with active mass transfer (cataclysmic variables)
from 5 to 11 systems. Our past Cycles 8 and 11 STIS observations of the
first 2 known, followed by our Cycle 13 SBC observations of the next 3 discovered,
revealed the clear presence of the white dwarf and increased amplitude
of the pulsations in the UV compared to the optical. The temperatures
derived from the UV spectra show 4 systems are much hotter than non-interacting
pulsating white dwarfs. A larger sample is needed to sort out the
nature of the instability strip in accreting pulsators i.e. whether effects
of composition and rotation due to accretion result in a well-defined instability
strip as a function of Teff. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11164 Title:
Molecular
Hydrogen Disks Around T Tauri Stars PI:
David
Weintraub PI
Institution:
Vanderbilt
University We
propose to measure the properties of planetary system-sized disks around Sun-like,
pre-main sequence stars by imaging the inner parts of these disks for
the first time in gaseous emission from their most dominant constituent, molecular
hydrogen gas. Specifically, we will use the F212N filter and NICMOS to
determine the spatial distribution of ro-vibrational H2 emission from protoplanetary
disks around selected classical and weak-lined T Tauri stars. The
target stars are among those detected by members of this team through
high resolution,
ground-based infrared spectroscopy. The spectra reveal H2 emission at
the rest velocities of the stars and at positions spatially coincident
with the
stars at the spatial resolution of the spectroscopic data. This imaging experiment,
which is impossible to do using ground-based facilities, is possible
using the NICMOS camera aboard the HST because the point spread function
of this system is extremely stable and can be measured to a very high accuracy.
This experiment is an important test of the interpretation that the 2.122
micron H2 line emission seen toward T Tauri stars is produced at distances
of 10 to 30 AU from the stars, the region in which giant planets are expected
to form around these stars. These observations will contribute toward developing
a better understanding of the process, likelihood, and timescale for
the formation of planets around Sun-like stars. ====================================================================== Proposal
Category: GO Scientific
Category: STAR FORMATION ID:
11165 Title:
The
Radius of the "Super-Neptune" HD 149026b PI:
Joshua
Winn PI
Institution:
Massachusetts
Institute of Technology Current
measurements suggest that the transiting exoplanet HD 149026b is a "super-Neptune,"
with an enormous heavy-element core. The existence of such a planet
is a major challenge to planet formation theories. We propose to place the
radius measurement on much firmer footing, by obtaining a NICMOS light curve
with 0.4 mmag precision and 13 sec cadence. We will improve the radius measurement
by a factor of 2.3, and more importantly, the result will be more robust
because we will determine the stellar radius directly from the data. Numerous
attempts to do this from the ground have failed. ====================================================================== Proposal
Category: GO Scientific
Category: AGN/QUASARS ID:
11166 Title:
The
Mass-dependent Evolution of the Black Hole-Bulge Relations PI:
Jong-Hak
Woo PI
Institution:
University
of California - Santa Barbara In
the local universe, the masses of giant black holes
are correlated with the
luminosities, masses and velocity dispersions of their host galaxy
bulges. This
indicates a surprisingly close connection between the evolution of galactic
nuclei (on parsec scales) and of stars on kpc scales. A key observational
test of proposed explanations for these correlations is to measure
how they have evolved over cosmic time. Our ACS imaging of 20 Seyfert 1
galaxies at z=0.37 showed them to have smaller bulges (by a factor of
3) for a
given central black hole mass than is found in galaxies in the
present-day universe.
However, since all our sample galaxies had black hole masses in the range
10^8.0--8.5 Msun, we could only measure the OFFSET in black hole mass to bulge
luminosity ratios from the present epoch. By extending this study to black
hole masses another factor of 10 lower, we propose to determine the full CORRELATION
of black hole mass with host galaxy properties at a lookback time of
4 Gyrs and to test mass-dependency of the evolution. We have selected 14 Seyfert
galaxies from SDSS DR5 whose narrow Hbeta emission lines (and estimated
nuclear luminosities) imply that they have black hole masses around 10^7
Msuns. We will soon complete our Keck spectroscopic measures of their bulge
velocity dispersions. We need a
1-orbit NICMOS image of each galaxy to separate
its nonstellar luminosity from its bulge and disk. This will allow us to
make the first determination of the full black hole/bulge relations at z=0.37
(e.g. M-L and M-sigma), as well as a test of whether active galaxies obey
the Fundamental Plane relation at that epoch. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11167 Title:
A
Unique High Resolution Window to Two Strongly Lensed Lyman Break
Galaxies PI:
Sahar
Allam PI
Institution:
Fermi
National Accelerator Laboratory (FNAL) On
rare occasions, the otherwise very
faint Lyman Break Galaxies (LBGs) are magnified by gravitational lensing to provide
exceptional targets for detailed
spectroscopic and imaging studies. We propose HST WFPC2 and NICMOS imaging
of two strongly lensed Lyman Break Galaxies (LBGs)
that were recently discovered by members of our
team. These
two LBGs -- the "8 O'Clock Arc" and
the "SDSS J1206+5142
Arc" -- are currently the
brightest known LBGs, roughly
3 times brighter than the
former record-holder, MS1512-cB58
(a.k.a. "cB58").
The z=2.73 "8 O'Clock Arc" extends ~10 arcsec in length and is magnified
by a factor of 12. The z=2.00
"SDSS J1206+5142 Arc" also extends ~10
arcsec in length and is magnified by a factor of 30.
Due to their brightness
and magnification, these two strongly lensed LBGs offer an unprecedented
opportunity for the very detailed investigation of two individual
galaxies at high redshift.
We are currently pursuing a vigorous ground-based
campaign to obtain multi-wavelength (UV,
optical, NIR, radio) observations
of these two
LBGs, but our
campaign currently lacks a
means of
obtaining high-resolution
optical/NIR imaging -- a lack that
currently only
HST can address. Our prime objective for this proposal is to obtain high resolution
HST images of these two systems with
two-orbit WFPC2 images in the BVI
bands and two-orbit NICMOS/NIC2 images in the J
and H bands. These data will
allow us to construct detailed lensing models, probe the mass and light profiles
of the lenses and their environments, and constrain the star formation
histories and rest-frame UV/optical spectral energy distributions of the
LBGs. ====================================================================== Proposal
Category: GO Scientific
Category: STAR FORMATION ID:
11168 Title:
The
IMF in the Hidden Galactic Starburst W49A PI:
Bernhard
Brandl PI
Institution:
Universiteit
Leiden W49A
is one of the most luminous and prolific massive star formation regions in
the disk of our Milky Way. Given the presence of several very massive OB clusters
as well as an unusually high concentration of many young ultra- compact
HII regions (UCHIIR) -- all embedded in about 1 million solar masses of
molecular gas -- it is arguably the best Galactic template for a
luminous starburst
region. We propose to obtain
NICMOS imaging of the central part of W49A,
covering a strip from the central, massive OB cluster to the ring of UCHIIRs.
Our goals are to resolve and characterize the central star cluster and
determine its IMF down to about 1 solar mass. We want to characterize
the distribution
of intermediate-mass YSOs, and identify the NIR counterparts to the
UCHIIRs. The combination of the proposed HST/NICMOS data with our
recently obtained
Spitzer observations would allow a great step forward in the understanding
of massive star and cluster formation. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11169 Title:
Collisions
in the Kuiper belt PI:
Michael
Brown PI
Institution:
California
Institute of Technology For
most of the 15 year history of observations of Kuiper belt objects, it
has been
speculated that impacts must have played a major role in shaping the physical
and chemical characteristics of these objects, yet little direct evidence
of the effects of such impacts has been seen. The past 18 months, however,
have seen an explosion of major new discoveries giving some of the first
insights into the influence of this critical process. From a diversity of
observations we have been led to the hypotheses that:
(1) satellite-forming impacts
must have been common in the Kuiper belt; (2) such impacts led to significant
chemical modification; and (3) the outcomes of these impacts are sufficiently
predictable that we can now find and study these impact-derived systems
by the chemical and physical attributes of both the satellites and the primaries.
If our picture is correct, we now have in hand for the first time a set
of incredibly powerful tools to study the frequency and outcome of collisions
in the outer solar system. Here we propose three linked projects that
would answer questions critical to the multiple prongs of our
hypothesis. In
these projects we will study the chemical effects of collisions through spectrophotometric
observations of collisionally formed satellites and through the
search for additional satellites around primaries with potential impact signatures,
and we will study the physical effects of impacts through the examination
of tidal evolution in proposed impact systems. The
intensive HST program
that we propose here will allow us to fully test our new hypotheses and
will provide the ability to obtain the first extensive insights into
outer solar
system impact processes. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11170 Title:
UV
Imaging of the Martian Corona and the Escape of Hydrogen PI:
John
Clarke PI
Institution:
Boston
University ACS
SBC UV imaging observations of Mars are proposed to study the extended hydrogen
corona, with application to the escape of hydrogen and the history of water
on Mars. These observations will
be scheduled when Mars is distant from the
Earth, so that a field of view of +/- 4-5 Mars radii can be obtained to image
the full range of the highly extended martian hydrogen corona through its
H Ly alpha emission. The
observations will also be obtained when the Sun- Earth-Mars
angle is close to 90 degrees, so that any asymmetry along the Mars- Sun
line can be observed. The observed
2-dimensional brightness distribution will
be related to local density using two existing radiative transfer codes, and
the upward flux and velocity distributions will be determined by comparison
with runs from an exospheric distribution model. These observations,
combined with simultaneous Ly alpha observations by the SPICAM instrument
on Mars Express from within the atmosphere, will provide the first tight
constraints on the total escape flux and importance of nonthermal processes
on the rate of escape. ====================================================================== Proposal
Category: GO Scientific
Category: ISM IN EXTERNAL GALAXIES ID:
11171 Title:
Confirming
Light Echoes from SN 2006X in M100 PI:
Arlin
Crotts PI
Institution:
Columbia
University in the City of New York We
propose a minimal investment of spacecraft time to discover and confirm
a light
echo from Supernova 2006X in M100, the closest Type Ia in many years. Our
spectroscopic and photometric data indicate that this SN sits behind a large
amount of interstellar dust likely to produce a strong echo signal. This
is one of very few cases where we will be able to study the three- dimensional
environment of a SN Ia in full detail, and begin to understand how environmental
effects play into the evolutionary and observational factors which
influence the utility of SN Ia as standard candles for probing cosmology. We propose an efficient program to
definitively detect (or not) a light
echo of reasonable signal strength, to confirm that it is an echo by demonstrating
apparent superluminal motion if it exists, to map the three- dimensional
geometry of the reflecting interstellar structures, and to detail the
reflectance properties of the dust which can be used to constrain its grain
size and composition distribution. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11172 Title:
Defining
Classes of Long Period Variable Stars in M31 PI:
Arlin
Crotts PI
Institution:
Columbia
University in the City of New York We
propose a thrifty but information-packed investigation (1440 exposures total)
with NICMOS F205W, F160W and F110W providing crucial information about Long
Period Variables in M31, at a level of detail that has recently allowed the
discovery of new variable star classes in the Magellanic Clouds, a very different
stellar population. These
observations are buttressed by an extensive
map of the same fields with ACS and WFPC2 exposures in F555W and F814W,
and a massive ground-based imaging patrol producing well-sampled light curves
for more than 400,000 variable stars.
Our primary goal is to collect sufficient
NIR data in order to analyze and classify the huge number of long- period
variables in our catalog (see below) through Period-Luminosity (P/L) diagrams. We will produce accurate P/L diagrams
for both the bulge and a progression
of locations throughout the disk of M31.
These diagrams will be similar
in quality to those currently in the Magellanic Clouds, with their lower
metallicity, radically different star formation history, and larger spread
in distance to the variables. M31
offers an excellent chance to study more
typical disk populations, in a manner which might be extended to more distant
galaxies where such variables are still visible, probing a much more evenly
spread progenitor age distribution than cepheids (and perhaps useful as a
distance scale alternative or cross-check). Our
data will also provide a massive
and unique color-magnitude dataset, and
allow us to confirm the microlensing
nature of a large sample of candidate lensed sources in M31. We expect
that this study will produce several important results, among them a better
understanding of P/L and P/L-color relations for pulsating variables which
are essential to the extragalactic distance ladder, will view these variables
at a common distance over a range of metallicities (eliminating the distance-error
vs. metallicity ambiguity between the LMC and SMC), allow further
insight into possible faint-variable mass-loss for higher metallicities,
and in general produce a sample more typical of giant disk galaxies
predominant in many studies. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11173 Title:
Completing
an Accurate Map of M31 Microlensing PI:
Arlin
Crotts PI
Institution:
Columbia
University in the City of New York The
halo microlensing masses detected in the MACHO survey (claimed to
compose about
20% of the Galaxy's mass) represent a major enigma in astrophysics, one that
must be effectively cross-examined by an independent test.
We have completed
a large, densely-sampled survey of M31 that can reveal in another galaxy
such a halo microlensing signal if it exists. In
a previous HST/ACS+WFPC2
program (GO 10273, Cycle 13, 16 orbits) we were able to learn considerably
more about a subsample of these M31 microlensing events.
We were pleased
to find that in most cases we could isolate the source star for each event,
find its baseline flux and colors (essential for ruling out classes of confusing
variable stars), test for misidentification of background supernovae,
and measure the Einstein parameters, which constrain the range of most
likely lens mass. (These Cycle 13
results are published in The Astrophysical
Journal Letters.) We propose to
finish the job, taking a similar
series of exposures to more than double the sample of well-constrained microlensing
events, which together with the larger ground-based sample for which
we are completing our analyses will provide 20-30 M31 bona fide microlensing
events observed by HST. This will
be done via a series of targetted
PC exposures, meant to maximize the number of candidates studied, one
(or two) at a time. A sample of
this size and quality should be sufficient
to settle the issue of a significant contribution to the halos of galaxies
by stellar-mass lenses.
Furthermore, if there is a surplus of such microlensing
events above what might be expected from stars alone, the higher quality
of information will allow us to more accurately describe the spatial distribution
of these lenses. We will also
complete several unique studies of M31
stellar populations, both in support of the microlensing measurement and in
their own right. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11174 Title:
A
Spitzer/X-ray candidate cluster at z>2:
NICMOS
imaging PI:
Emanuele
Daddi PI
Institution:
Commissariat
a l'Energie Atomique (CEA) We
propose deep H-band imaging with NICMOS of a remarkable z>2 cluster
of galaxy
candidate. Over a 1000 arcmin^2 field imaged with Spitzer's IRAC and MIPS
we have discovered a compact (<30'' diameter) concentration of
extremely red
galaxies with a factor of >40 overdensity over the adjacent field.
Among these
galaxies for which we can derive meaningful photometric redshifts, 17 are
consistent with zphot=2-2.5, making very likely that the concentrationis is
a real cluster at such high redshift. This is further supported by a 3.5 sigma
detection of extended X-Ray emission on Newton-XMM data, by a likely color-magnitude
sequence of red galaxies, and by the presence of a giant galaxy
consistent with a BCG at the cluster redshift. While spectroscopic confirmation
of the cluster might result prohibitive with current facilities, HST
high resolution imaging will allow us to gain crucial information for
the study
and scientific exploitation of this hot gas hosting, record high-z cluster
of galaxies. The HST high resolution observations will allow us to unveil
the rest frame optical morphologies of
the galaxies and confirm the presence
of ellipticals in the structure, detect and characterize the color- magnitude
relation, measure their effective radii and construct their Kormendy relation
for the passively evolving subsample, improve the photometric redshift
estimates to confirm the real cluster nature of the structure, estimate
stellar masses and check for possible deviations from the local mass- size
relation, search for mergers and AGNs, and establish a cluster benchmark for
cluster-field comparisons at this highest redshift. ====================================================================== Proposal
Category: GO Scientific
Category: UNRESOLVED STELLAR POPULATIONS ID:
11175 Title:
UV
Imaging to Determine the Location of Residual Star Formation in
Galaxies
Recently Arrived on the Red Sequence PI:
Sandra
Faber PI
Institution:
University
of California - Santa Cruz We
have indentified a sample of low-redshift (z = 0.04 - 0.10) galaxies
that are
candidates for recent arrival on the red sequence.
They have red optical colors
indicative of old stellar populations, but blue UV-optical colors that could
indicate the presence of a small quantity of continuing or very recent star
formation. However, their spectra
lack the emission lines that characterize
star-forming galaxies. We propose
to use ACS/SBC to obtain high- resolution
imaging of the UV flux in these galaxies, in order to determine the spatial
distribution of the last episode of star formation.
WFPC2 imaging will
provide B, V, and I photometry to measure the main stellar light distribution
of the galaxy for comparison with the UV imaging, as well as to measure
color gradients and the distribution of interstellar dust.
This detailed
morphological information will allow us to investigate the hypothesis that
these galaxies have recently stopped forming stars and to compare the observed
distribution of the last star formation with predictions for several different
mechanisms that may quench star formation in galaxies. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11176 Title:
Location
and the Origin of Short Gamma-Ray Bursts PI:
Andrew
Fruchter PI
Institution:
Space
Telescope Science Institute During
the past decade extraordinary progress has been made in determining the origin
of long-duration gamma-ray bursts.
It has been conclusively shown that
these objects derive from the deaths of massive stars.
Nonetheless, the origin
of their observational cousins, short-duration gamma-ray bursts (SGRBs) remains
a mystery. While SGRBs are
widely thought to result from the inspiral
of compact binaries, this is a conjecture. A
number of hosts of SGRBs
have been identified, and have been used by some to argue that SGRBs derive
primarily from an ancient population (~ 5 Gyr); however, it is not known
whether this conclusion more accurately reflects selection biases or astrophysics. Here we propose to employ a variant of
a technique that we pioneered
and used to great effect in elucidating the origins of long-duration bursts. We will examine the degree to
which SGRB locations trace the red or blue
light of their hosts, and thus old or young stellar populations. This approach
will allow us to study the demographics of the SGRB population in a manner
largely free of the distance dependent selection effects which have so far
bedeviled this field, and should give direct insight into the age of the SGRB
progenitor population. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11177 Title:
The
Nature of z=3 Lyman-Alpha Emitters PI:
Caryl
Gronwall PI
Institution:
The
Pennsylvania State University The
advent of large mosaic CCD cameras on 4 -- 8 m class telescopes has recently
led to a revolution in our ability to detect primordial galaxies. Today,
large numbers of strong Ly-alpha
emitters (LAEs) are being discovered between
2.4 < z < 6. These are
important objects: not
only do they sample a part
of the galaxy luminosity function that is inaccessible to the
Lyman-break technique,
but they also tend to be younger and less chemically evolved. In fact,
the LAEs now being found are currently our best candidates for galaxies in
the act of formation. To
investigate the properties of this class of objects,
we have conducted an extremely deep narrow-band (5000 Angstrom; FWHM =
50 Angstrom) and broad-band (UBVRIzJK) survey of the Extended Chandra
Deep Field
South, and have identified a homogeneous sample of strong Ly-alpha emitters
at z = 3.11. Twenty-seven of these
objects are located within the region
surveyed by Great Observatories Origins Deep Survey (GOODS) and have detailed
morphological information available from the rest-frame ultraviolet. We
propose 0.2" resolution narrow-band imaging of 11 of our LAEs using the F502N
filter of WFPC2. By comparing the
Ly-alpha and rest-frame UV continuum morphologies
of these galaxies, we will be able to look for the presence of outflows,
constrain their dust content, and test whether these objects are truly
primordial galaxies. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11178 Title:
Probing
Solar System History with Orbits, Masses, and Colors of Transneptunian
Binaries PI:
William
Grundy PI
Institution:
Lowell
Observatory The
recent discovery of numerous transneptunian binaries (TNBs) opens a
window into
dynamical conditions in the protoplanetary disk where they formed as
well as
the history of subsequent events which sculpted the outer Solar System
and emplaced
them onto their present day heliocentric orbits. To
date, at least 43
TNBs have been discovered, but only about a dozen have had their mutual orbits
and separate colors determined, frustrating their use to investigate numerous
important scientific questions.
The current shortage of data especially
cripples scientific investigations requiring statistical comparisons
among the ensemble characteristics.
We propose to obtain sufficient
astrometry and photometry of 23 TNBs to compute their mutual orbits and
system masses and to determine separate primary and secondary colors, roughly
tripling the sample for which this information is known, as well as extending
it to include systems of two near-equal size bodies.
To make the most
efficient possible use of HST, we will use a Monte Carlo technique to optimally
schedule our observations. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11179 Title:
Dynamics
of Clumpy Supersonic Flows in Stellar Jets and in the Laboratory PI:
Patrick
Hartigan PI
Institution:
Rice
University We
propose to reobserve three stellar jets in order to quantify how rapidly clumps
in these flows accelerate and decelerate, and to compare the results with
ongoing numerical simulations and laboratory experiments. Each jet has been
imaged twice before with HST, and precise proper motions have been measured
for all emitting knots in the jets. Images from the first two epochs show
clear differential motions between adjacent clumps, as well as shear,
and possibly
fragmentation. The proposed third epoch will enable us to measure the first
ever accelerations in jets, quantify errors in existing proper motion measurements,
and observe in real time how fluid instabilities develop in supersonic
flows. The new images will make it possible to compare the behavior of
astrophysical flows directly with numerical simulations and with
laboratory experiments
of bow shocks and clumpy flows in progress at the Omega laser facility. ====================================================================== Proposal
Category: GO Scientific
Category: COOL STARS ID:
11180 Title:
The
Morphology of the Post-Red Supergiant IRC+10420's Circumstellar Ejecta PI:
Roberta
Humphreys PI
Institution:
University
of Minnesota - Twin Cities The
extremely luminous post-red supergiant and powerful OH/IR source IRC +10420
is surrounded by a complex circumstellar nebula. Numerous small condensations,
arcs, jet-like rays of knots, and intriguing semi-circular structures
are easily visible in our previous WFPC2 images. We have suggested that
these spatially recognizable features may be evidence for episodic mass loss
events possibly from localized active regions. We now propose to obtain second
epoch WFPC2 images with the Planetary Camera to measure the transverse motions
of these ejecta. Spatially resolved spectra from STIS showed that the embedded
arcs are kinematically distinct from the spherically expanding diffuse
nebulosity. The transverse motions in combination with radial velocities
from the STIS spectra, will let us determine the morphology of IRC +10420's
nebula and the structures embedded in it, its mass loss history, and provide
clues to the mass loss mechanism responsible for the discrete ejections. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11181 Title:
SAINTS
- Supernova 1987A INTensive Survey PI:
Robert
Kirshner PI
Institution:
Harvard
University SAINTS
is a program to observe SN 1987A, the brightest supernova in 383 years, as
it matures into the youngest supernova remnant at age 20.
HST is the essential
tool for spatially-resolved observations of SN1987A's many components. A violent encounter is now underway
between the fastest-moving debris
and the circumstellar ring: the shock
excites "hotspots." The
optical, infrared
and X-ray fluxes are rising rapidly on 6-month time scales:
we
have organized
HST, SPITZER, and CHANDRA observations to understand these regions. In
Cycle 16, the separate hotspots may begin to fuse as the shock fully
enters the
circumstellar ring. Photons from
these shocks will excite previously invisible
gas outside the ring, revealing the true extent of the mass loss that
preceded the explosion of Sanduleak -69 202. The inner debris of the explosion,
excited by radioactive isotopes from the explosion, is now resolved and
seen to be aspherical, providing direct evidence on the asymmetry of the explosion. Questions about SN 1987A remain
unanswered. How did the enigmatic three
rings form? Precisely what
happened during the core collapse and bounce? Is a black hole or a neutron star left
behind? The rich and deep data
set from SAINTS will help answer these central questions of supernova science. ====================================================================== Proposal
Category: GO Scientific
Category: RESOLVED STELLAR POPULATIONS ID:
11182 Title:
The
Mass of the Milky Way:
Orbits
for Leo I and Leo II: Second Epoch Imaging of Leo II PI:
Konrad
Kuijken PI
Institution:
Universiteit
Leiden Constraining
the mass of the Galaxy at large radii remains a difficult problem. Available data are still rather scarce,
and orbits of even a few objects
at large radii can have a large impact.
We propose to obtain proper motions
for the two satellites Leo I and Leo II, which orbit the Galaxy at about
200 kpc. Together with the radial
velcoities of these glaaxies, which are
well known, the proper motions allow space velocities ot be consructed: these
can remove signifiicant uncertainty in the Galactic mass models, and in particular
settle the vexed question of whether or not Leo I is gravitationally
bound to the Galaxy. The proper
motion of Leo I is addressed in
a companion archival proposal; here we address the WFPC2 imagery of Leo
II. ====================================================================== Proposal
Category: GO Scientific
Category: ISM IN EXTERNAL GALAXIES ID:
11183 Title:
Ultraviolet
Imaging of Lyman-Alpha-Selected Galaxies at High Redshift PI:
Crystal
Martin PI
Institution:
University
of California - Santa Barbara We
propose to carry out deep NICMOS/NIC2 imaging in the rest-frame, ultraviolet
continuum of galaxies discovered in the Magellan Multi-Slit Lyman Alpha
Survey. This spectroscopic survey
identified
ultra-faint, redshift 5.7 Lyman-alpha
emitters (LAEs) in a 15 nm wide, OH-free band at 819 nm.
Imaging with
HST is the only way to measure their continuum intensity near rest-frame 160
nm. The ultraviolet photometry
will directly measure the rate of star formation
in common objects; and, when combined with groundbased Lyman-alpha luminosities,
provide a reliable cross-calibration of Lyman-alpha attenuation and
emission equivalent width. Direct
measurement of the size of the star- forming
regions, unresolved in the groundbased data, will extend measurements of
the intensity of star formation to common objects in the high-redshift universe. Gaseous outflows from these galaxies
are thought to be the source of
their asymmetric line profiles, and area-averaged star formation rates
are needed
to calibrate feedback recipes, as well as eventually extend the Schmidt-Kennicutt
law to high-redshift. The three
targets proposed in Cycle~16
lie in fields covered by major galaxy surveys, are not as bright as the
unusually luminous sources identified by such surveys at high-redshift, and
present an opportunity to study properties of more common galaxies at high-redshift. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11184 Title:
Imaging
the Shock Precursor in Tycho's SNR PI:
John
Raymond PI
Institution:
Smithsonian
Institution Astrophysical Observatory Cosmic
ray acceleration in supernova remant shocks requires shock precursors where
particles are trapped by plasma turbulence. The
precursors also heat and
compress the upstream gas, producing H alpha emission and affecting line profiles. We propose to image the brightest
non-radiative shock in Tycho's SNR
to measure the brightness and width of the precursor.
These measurements will
constrain 2 key parameters in cosmic ray acceleration models, and they will
improve the accuracy of shock speed and electron-ion equilibration derived
from H alpha profiles. ====================================================================== Proposal
Category: GO Scientific
Category: ISM AND CIRCUMSTELLAR MATTER ID:
11185 Title:
Search
for H-poor/He-rich Inclusions and a Solution to the Abundance,
Temperature
Problems PI:
Robert
Rubin PI
Institution:
NASA
Ames Research Center Our
recent abundance survey of a large sample of Galactic planetary nebulae (PNe)
has led to the discovery of a group
of super-metal-rich nebulae whose spectra
are characterized by prominent optical recombination lines (ORLs) from C,
N, O, & Ne ions and a large Balmer discontinuity jump. The heavy
element abundances
derived from ORLs for several PNe are more than an order of magnitude
higher than those derived from the traditional method based on collisionally
excited lines (CELs), while the Balmer jump yields electron temperatures
(Te) significantly lower than values derived from the [O III] 5007/4363
CEL line ratio. A
proposition that aspires to explain both the nebular
abundance and Te problems is one
according to which these nebulae contain
(at least) two distinct emission regions - one of "normal" Te (~
10000 K)
and chemical composition (~solar) and another of very low Te that is H- deficient,
thus having high helium and metal abundances relative to hydrogen. The
latter component emits strong He and heavy element ORLs but essentially
no CELs.
The consistent picture that emerges from fitting a 2-component photoionization
model to the spectroscopic data is that the H-poor component is
in high-density inclusions, which provide only a minor fraction of the total
nebular mass. We propose to directly detect these inclusions in the planetary
nebula M 1-42 using WFPC2 (PC) to make a high spatial resolution image
in the He I 5876 A ORL
and ratio it to Halpha. With NICMOS
(NIC1), we plan
to observe the He I 10830 A line, which is substantially
collisionally excited,
along with Palpha 18760 A. The ratio image of He I 10830 to Palpha is expected
to be less likely to show the
inclusions, thus serving as an important
control to the optical imaging. M 1-42 is one of the most extreme cases
of the abundance and Te problem; it is reasonably bright and compact. This
program has the potential to resolve a serious challenge to our current understanding
of nebular astrophysics. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11186 Title:
Investigation
of the spatial and temporal structure of Europa's atmospheric emissisons PI:
Joachim
Saur PI
Institution:
Universitat
zu Koeln We
propose to explore the spatial structure and temporal variability of Europa's
O2 atmosphere with ACS/SBC. Previous HST images display non-uniform UV
emission from Europa's atmosphere, which maximizes within the disk of Europa
on its anti-Jovian northern quadrant. These images were taken at western
elongation and are not conclusive,
but bring up the exciting question whether
the non-uniform emission is due to a locally enhanced
neutral atmosphere.
A locally inhomogeneous atmosphere would imply locally modified surface properties. This might provide clues on
inhomogeneities of the underlying
ice structure and thus properties of a
potential subsurface ocean. Since
the inhomogeneous emission comes from within the disk of Europa, we propose
to study Europa at eastern and western elongation to decide if the locally
enhanced emission is truly an
atmospheric effect. We propose to take for
each elongation five contiguous observations within one rotation period of
Jupiter to discriminate between a competing effect that produces inhomogeneous
emission patterns, i.e., the
electrodynamic interaction with Jupiter's
magnetosphere. We will use ACS/SBC with PR130L prism to
completely separate
the two prominent FUV oxygen lines OI 1304 A and OI 1356 A emitted from
Europa's atmosphere. ====================================================================== Proposal
Category: GO Scientific
Category: SOLAR SYSTEM ID:
11187 Title:
A
Deep Search for Martian Dust Rings PI:
Mark
Showalter PI
Institution:
SETI
Institute It
has been long suspected that Mars is encircled by two faint rings of
dust, one
originating from each of its moons Phobos and Deimos. Similar dust rings are
associated with many of the small, inner moons orbiting Jupiter, Saturn, Uranus
and Neptune. On December 31, 2007, Earth will pass through Mars' equatorial
plane just a week after its December 24 opposition, providing an exceedingly
rare opportunity to image the rings under nearly ideal viewing geometry.
The next equivalent viewing opportunity occurs in 2022. Using the Wide
Fields of WFPC2 and a highly optimized observing plan, we expect to be able
to detect rings with edge-on reflectivities of ~ 10^-8, which is at or below
the level where most dynamicists expect rings to be visible. This is a factor
of 10-30 more sensitive than the detection limit we achieved during a slightly
inferior viewing opportunity in 2001. The rings have been predicted to
show some interesting dynamical properties, including large asymmetries
and inclinations.
A positive detection will test these predictions, serving as an effective
test of dynamical models developed to account for the properties of other
faint planetary rings as well. With such a stringent limit, even a negative
result will be of considerable interest, challenging dynamicists to explain
the remarkably low density of dust within the Martian system. ====================================================================== Proposal
Category: GO Scientific
Category: COSMOLOGY ID:
11188 Title:
First
Resolved Imaging of Escaping Lyman Continuum PI:
Brian
Siana PI
Institution:
Jet
Propulsion Laboratory The
emission from star-forming galaxies appears to be responsible for reionization
of the universe at z>6.
However, the models that attempt to describe
the detailed impact of high-redshift galaxies on the surrounding inter-galactic
medium (IGM) are strongly dependent upon several uncertain parameters. Perhaps the most uncertain is the
fraction of HI-ionizing photons produced
by young stars which escape into the IGM.
Most attempts to measure this
"escape fraction" (f_esc) have produced null results.
Recently, a small subset
of z~3 Lyman Break Galaxies (LBGs) has been found exhibiting large escape
fractions. It remains unclear
however, what differentiates them from other
LBGs. Several models attempt to
explain how such a large fraction of ionizing
continuum can escape through the HI and dust in the ISM (eg. "chimneys"
created by SNe winds, globular cluster formation, etc.), each producing
unique signatures which can be observed with resolved imaging of the escaping
Lyman continuum. We propose a
deep, high resolution WFPC2 image of the
ionizing continuum (F336W) and the rest-frame 1500 Angstrom continuum (F606W)
of five of the six known LBGs with large escape fractions.
These LBGs all
fit within a single WFPC2 pointing, yielding high observing efficiency. Additionally,
they all have z~3.1 or higher, the optimal redshift range for probing
the Lyman Continuum region with available WFPC2 filters.
These |