Cycle 14 Abstract Catalog
Generated from Phase I Submissions
April 06, 2005
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Proposal Category: GO
Scientific Category: COSMOLOGY
ID: 10486
Title: A Cosmic String Lens Candidate
PI: Eric Agol
PI Institution: University of Washington
We propose two-band imaging observations with ACS of a cosmic string lens
candidate, CSL-1, to look for a feature predicted by the cosmic string model:
a low-surface brightness discontinuity in between the two galaxy images.
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Proposal Category: GO
Scientific Category: STAR FORMATION
ID: 10487
Title: A Search for Debris Disks in the Coeval Beta Pictoris
Moving Group
PI: David Ardila
PI Institution: The Johns Hopkins University
Resolved observations of debris disks present us with the opportunity of
studying planetary evolution in other solar systems. We propose to search for
debris disks in the Beta Pictoris moving group (8-20 Myrs, 10-50 pc away) ,
which provides a coeval sample of multiple spectral types, and it has already
produced two magnificent resolved debris disks: AU Mic and Beta Pic. Such
coeval sample will provide us with a snapshop of the crucial time in disk
evolution in which the disk makes the transition from optically thick to
optically thin, and it will be useful to study the stellar mass dependence of
the disk evolution.
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Proposal Category: SNAP
Scientific Category: GALAXIES
ID: 10488
Title: The Most Massive Galaxies in the Universe: Color-
Gradients and Texture
PI: Mariangela Bernardi
PI Institution: University of Pennsylvania
We are proposing an HST snapshot survey of 40 objects with velocity dispersion
larger than 350 km/s, selected from the Sloan Digital Sky Survey and confirmed
to be single massive galaxies by the ACS-HRC i-band imaging obtained during
Cycle 13. This sample of the most massive galaxies in the Universe is
interesting because these objects potentially harbor the most massive black
holes, and because their existence places strong constraints on galaxy
formation models. These objects are unusual for another reason than their
abnormally large velocity dispersions: they appear to be bluer than expected
from extrapolation of the color-velocity dispersion relation of normal early-
types to these large velocity dispersions. The bluer than expected colors
indicate that the formation histories of these objects are likely to be rather
different than for normal early-types. This difference is also expected to
manifest as abnormal color-gradients. ACS-HRC imaging in one other band (i.e.
the g-band) will allow us not simply to analyze color gradients in these
objects but also to study their color texture and topology. This study will
provide important information about the formation history of galaxies.
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Proposal Category: GO
Scientific Category: STAR FORMATION
ID: 10489
Title: Imaging Extended UV H2 Emission Around T Tauri
PI: Alexander Brown
PI Institution: University of Colorado at Boulder
The interactions between the circumstellar disk, newly-forming star, and
bipolar jet outflows play a central role in the process of star formation.
These interactions control how disks evolve and dissipate, and, thereby,
control the process of planetary system formation. We propose to image the UV
molecular hydrogen (H2) emission around the pre-main-sequence binary star T
Tauri using the ACS SBC (solar blind channel) MAMA detector, thus determining
the spatial properties of the H2 emitting regions, and deriving important
detailed observational information on the disk-star-jet interaction on scales
of order 5 AU. These images will reveal the degree of collimation and opening
angles of the innermost parts of the high velocity jets, the shock structure
within the jet outflows, the size and morphology of the circumstellar disks,
both in emission and in silhouette, and the conditions inside the polar
cavities swept clear by Herbig-Haro flows. Fluorescent H2 emission lines
dominate the UV spectrum of T Tau. Long-slit (1-D) STIS UV spectra of T Tau
show H2 emission with a complex spatial structure extending many arcseconds
from the star and the presence of significant shock structures. The H2 must be
warm (approx. 2000 K) for the fluorescence to operate. The molecular emission
originates in shocks and, perhaps, also from the surfaces of the inner
regions of accretion disks.
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Proposal Category: SNAP
Scientific Category: COSMOLOGY
ID: 10490
Title: A Snapshot Survey of a Complete Sample of X-ray Luminous
Galaxy Clusters from Redshift 0.3 to 0.7
PI: Megan Donahue
PI Institution: Michigan State University
We propose to extend a public, uniform imaging survey of a well-studied,
complete, and homogeneous sample of X-ray clusters. The sample of 72 clusters
spans the redshift range between 0.3-0.7 and almost 2 orders of magnitude of
X-ray luminosity, with a median luminosity of 10^44 erg/s (0.5-2.0 keV).
These snapshots will be used to obtain a fair census of the morphologies of
cluster galaxies in the cores of intermediate redshift clusters, to detect
radial and tangential arc candidates, to detect optical jet candidates, and to
provide an approximate estimate of the shear signal of the clusters themselves
and a potential assessment of the contribution of large scale structure to
lensing shear.
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Proposal Category: SNAP
Scientific Category: COSMOLOGY
ID: 10491
Title: A Snapshot Survey of the most massive clusters of
galaxies
PI: Harald Ebeling
PI Institution: University of Hawaii
We propose a snapshot survey of a sample of 124 high X-ray luminosity clusters
in the redshift range 0.3-0.7. Similarly luminous clusters at these redshifts
frequently exhibit strong gravitational lensing. The proposed observations
will provide important constraints on the nature of the cluster mass
distributions and a set of optically bright, lensed galaxies for further 8-10m
spectroscopy. We acknowledge the broad community interest in this sample and
waive our data rights for these observations.
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Proposal Category: GO
Scientific Category: COSMOLOGY
ID: 10492
Title: A detailed study of the mass properties for the galaxy
cluster RX J1347-1145
PI: Thomas Erben
PI Institution: Universitaet Bonn, Inst fur Astrophysik und
Extraterrestris
We propose to obtain deep, multi-colour imaging for the galaxy cluster RX
J1347-1145 at z=0.45. Together with our high-quality ground-based optical and
X-ray data sets already at hand this observation will produce a precise mass
determination of this most X-ray luminous cluster. The analysis will mainly
be carried out by a newly developed and novel technique that combines weak
and strong lensing information and which is able to break the mass-sheet
degeneracy that hampered most previous lensing mass determinations. Within
our extensive campaign to understand the mass properties of RX J1347-1145, the
main goal of the ACS images will be a refined, high-resolution lensing mass
reconstruction of the cluster core. This will be achieved by a substantially
increased number density of background sources for a weak lensing analysis in
combination with constraints from multiply lensed images that are identified
with morphology and colour information. Both of these require the unique
resolving power of ACS. RX J1347-1145 is an ideal candidate for elucidating
the discrepant mass estimates obtained from traditional methods. It plays the
same role at high redshift as A1689 at intermediate redshifts for which a
similar analysis has been performed with ACS. Our results will therefore be an
important ingredient in the use of galaxy clusters as cosmological probes.
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Proposal Category: GO
Scientific Category: COSMOLOGY
ID: 10493
Title: A Survey for Supernovae in Massive High-Redshift Clusters
PI: Avishay Gal-Yam
PI Institution: California Institute of Technology
We propose to measure, to an unprecedented 30% accuracy, the SN-Ia rate in a
sample of massive z=0.5-0.9 galaxy clusters. The SN-Ia rate is a poorly known
observable, especially at high z, and in cluster environments. The SN rate and
its redshift dependence can serve as powerful discrimiminants for a number of
key issues in astrophysics and cosmology. Our observations will: 1. Put clear
constraints on the characteristic SN-Ia "delay time," the typical time between
the formation of a stellar population and the explosion of some of its members
as SNe-Ia. Such constraints can exclude entire categories of SN-Ia progenitor
models, since different models predict different delays. 2. Help resolve the
question of the dominant source of the high metallicity in the intracluster
medium (ICM) - SNe-Ia, or core-collapse SNe from an early stellar population
with a top-heavy IMF, perhaps those population III stars responsible for the
early re-ionization of the Universe. Since clusters are excellent laboratories
for studying enrichment (they generally have a simple star-formation history,
and matter cannot leave their deep potentials), the results will be relevant
for understanding metal enrichment in general, and the possible role of first
generation stars in early Universal enrichment. 3. Reveal, via nuclear
variability, the AGN fraction in clusters at this redshift, to be compared
with the field AGN fraction. This will be valuable input for understanding
black-hole demographics, AGN evolution, and ICM energetics. 4. Potentially
discover intergalactic cluster SNe, which can trace the stripped stellar
population at high z.
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Proposal Category: GO
Scientific Category: GALAXIES
ID: 10494
Title: Imaging the mass structure of distant lens galaxies
PI: Leon Koopmans
PI Institution: Kapteyn Astronomical Institute
The surface brightness distribution of extended gravitationally lensed arcs
and Einstein rings contains super-resolved information about the lensed
object, and, more excitingly, about the smooth and clumpy mass distribution of
the lens galaxies. The source and lens information can non-parametrically be
separated, resulting in a direct "gravitational-mass image" of the inner mass-
distribution of cosmologically-distant galaxies (Koopmans 2005). With this
goal in mind, we propose deep HST ACS-F555W/F814W and NICMOS-F160W imaging of
15 gravitational-lens systems with spatially resolved lensed sources, selected
from the 17 new lens systems discovered by the Sloan Lens ACS Survey (Bolton
et al. 2004). Each system has been selected from the SDSS and confirmed in a
time-efficient HST-ACS snapshot program (cycle-13); they show highly-magnified
arcs or Einstein rings, lensed by a massive early-type lens galaxy. High-
fidelity multi-color HST images are required (not delivered by the 420-sec
snapshot images) to isolate these lensed images (properly cleaned, dithered
and extinction-corrected) from the lens galaxy surface brightness
distribution, and apply our "gravitational-mass imaging" technique. The
sample of galaxy mass distributions - determined through this method from the
arcs and Einstein ring HST images - will be studied to: (i) measure the smooth
mass distribution of the lens galaxies (Dark and luminous mass are separated
using the HST images and the stellar M/L values derived from a joint stellar-
dynamical analysis of each system); (ii) quantify statistically and
individually the incidence of mass-substructure (with or without obvious
luminous counter-parts such as dwarf galaxies). Since dark-matter substructure
should be considerably more prevalent at higher redshift, both results provide
a direct test of this prediction of the CDM hierarchical structure-formation
model.
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Proposal Category: GO
Scientific Category: GALAXIES
ID: 10495
Title: The Nuclear Environment of the Galaxy Hosting the Largest
Known Radio Outburst
PI: Brian McNamara
PI Institution: Ohio University
We propose to image the cD galaxy host of the most powerful radio outburst
known in the Universe. The outburst was identified in a Chandra image of a
z=0.216 galaxy cluster which revealed a pair of enormous cavities, each 200
kpc in diameter, embedded in its X-ray halo. The outburst began approximately
100 Myr ago and has expended 6x10^61 ergs. It is apparently powered by
accretion onto the cD's billion solar mass nuclear black hole, which grew
heavier by roughly 1/3 during the outburst. We intend to examine the
morphology and nuclear environment of the host galaxy to understand the
conditions that created this remarkable event.
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Proposal Category: GO
Scientific Category: COSMOLOGY
ID: 10496
Title: Decelerating and Dustfree: Efficient Dark Energy Studies
with Supernovae and Clusters
PI: Saul Perlmutter
PI Institution: University of California - Berkeley
We propose a novel HST approach to obtain a dramatically more useful "dust
free" Type Ia supernovae (SNe Ia) dataset than available with the previous
GOODS searches. Moreover, this approach provides a strikingly more efficient
search-and-follow-up that is primarily pre-scheduled. The resulting dark
energy measurements do not share the major systematic uncertainty at these
redshifts, that of the extinction correction with a prior. By targeting
massive galaxy clusters at z > 1 we obtain a five-times higher efficiency in
detection of Type Ia supernovae in ellipticals, providing a well-understood
host galaxy environment. These same deep cluster images then also yield
fundamental calibrations required for future weak lensing and Sunyaev-
Zel'dovich measurements of dark energy, as well as an entire program of
cluster studies. The data will make possible a factor of two improvement on
supernova constraints on dark energy time variation, and much larger
improvement in systematic uncertainty. They will provide both a cluster
dataset and a SN Ia dataset that will be a longstanding scientific resource.
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Proposal Category: GO
Scientific Category: COSMOLOGY
ID: 10497
Title: Cepheid Calibrations of the Luminosity of Two Reliable
Type Ia Supernovae and a Re-determination of the Hubble
Constant
PI: Adam Riess
PI Institution: Space Telescope Science Institute
We propose to determine the luminosity of two type Ia supernovae (SNe Ia),
1995al in NGC 3021 and SN 2002fk in NGC 1309, by observing Cepheids in their
spiral hosts. Modern CCD photometry yields an extremely tight Hubble diagram
for SNe Ia with a precisely determined intercept (i.e., Delta H_0/H_0). Yet,
the measurement of the true Hubble constant via SNe Ia is limited by the
calibration derived from problematic and unreliable SN data. Most of the SNe
Ia calibrated by HST to date are significantly compromised by the systematics
of photographic photometry, high reddening and SN peculiarity, and by the
photometric anomolies associated with WFPC2. The extended reach of ACS now
provides opportunities to more reliably calibrate SNe Ia and H_0. Our Cepheid
calibration of a reliable SN Ia dataset, SN 1994ae, using ACS in Cycle 11
resulted in a 15% increase in H_0 from the value derived by the HST SN Ia
Calibration Program. Yet, there remains a terribly small sample of reliable
SN Ia data sets on which to base such a crucial cosmological result. SN
1995al and SN 2002fk are two of the best observed SNe Ia both with little
reddening. They provide two opportunities to use ACS for placing the
calibration of H_0 via SN Ia on firmer footing and potentially improve its
precision.
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Proposal Category: GO
Scientific Category: HOT STARS
ID: 10498
Title: Detecting the progenitors of core-collapse supernovae
PI: Stephen Smartt
PI Institution: The Queen's University of Belfast
Modern supernovae searches in the nearby Universe are discovering large
numbers of SNe which have massive star progenitors (Types II, Ib and Ic). The
extensive HST image archives within ~20Mpc enables their indvidual bright
stellar content to be resolved. As massive, evolved stars are the most
luminous single objects in a galaxy, the progenitos of core-collapse SNe
should be directly detectable on pre-explosion images. Two recent highlights
of our ongoing HST programme are that we have detected the first red
supergiant progenitor of a normal type II supernova and shown that SN1993J
came from a binary system by detecting the companion star at the position of
the SN. We have detected a further two progenitor stars of normal type II-P
supernovae, set mass limits on a further 7 and suggest that faint type II
supernovae are unlikely to come from the collapse of very massive stars which
form black holes. These discoveries are providing strong constraints on
theoretical models of pre-supernova evolution and the origin of the supernova
types. We request time to continue this successful project and require ACS
observations of future SNe which are discovered in galaxies closer than 20Mpc
which have pre-explosion HST archive images available. This will allow the
SNe to be precisely positioned on the pre-explosion images. We have set a
final goal for this project of determining masses and types, or setting
restrictive mass-limits for 30 supernovae, before the demise of HST.
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Proposal Category: GO
Scientific Category: GALAXIES
ID: 10499
Title: Life Before the Fall: Morphological Evolution of
Galaxies in Groups Prior to Cluster Assembly at z=0.37
PI: Kim-Vy Tran
PI Institution: Eidgenossiche Technische Hochschule (ETH)
We propose to obtain a deep ACS/WFC mosaic of a protocluster comprised of 4
distinct galaxy groups that are gravitationally bound to each other at z=0.37.
The galaxy groups have a total combined mass comparable to the Coma cluster
and already have twice as many absorption line galaxies as the field. The
SG1120 complex thus provides an unprecedented opportunity for determining
whether "pre-processing" in the group environment is responsible for the bulk
of observed diffences between galaxies in nearby clusters and those in the
field. High resolution imaging with HST is needed to morphologically classify
the group members and measure their structural parameters. By combining the
early-type fraction and morphology-density relation in SG1120 with results
from our wide-field spectroscopic survey, we will test whether spectral and
morphological transformation timescales are decoupled on group scales and
isolate the environmental mechanisms responsible for such evolution. We will
also measure the Fundamental Plane and M/L ratios of the early-type members to
constrain their formation epoch and how their stellar populations have
evolved. Observations of the multiple galaxy groups in SG1120 provide a
unique dataset to the community and will aid our understanding of how galaxies
evolve in the still poorly studied group regime.
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Proposal Category: GO
Scientific Category: STELLAR POPULATIONS
ID: 10500
Title: Exploring the Bottom End of the White Dwarf Cooling
Sequence in the Galactic Open Cluster NGC2158
PI: Luigi Bedin
PI Institution: European Southern Observatory - Germany
The recent discovery by our group of an unexpectedly bright and still
unexplained peak in the white dwarf (WD) luminosity function (LF) of the metal
rich, old open cluster NGC6791 casts serious doubts on our understanding of
the physical process which rules the formation and the cooling of WDs. In
order to investigate whether the same problem is present in other open
clusters with different ages and metallicities, we propose deep ACS/HST
observations reaching the bottom end of the WD LFs, for the first time in a
young and so popolous Galactic open cluster: NGC2158.
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Proposal Category: GO
Scientific Category: STELLAR POPULATIONS
ID: 10501
Title: Extending the Heritage: Clusters, Dust, and Star
Formation in M51
PI: Rupali Chandar
PI Institution: Space Telescope Science Institute
Strongly interacting systems in the Local Universe offer the opportunity to
investigate the modality of star formation under dynamical conditions more
typical of the intermediate redshift Universe (z~0.5-1), at an exquisite
resolution unmatched by distant galaxies. M51 is one such system. Most
recently, the Hubble Heritage program dedicated 24 HST orbits to obtain a 3X2
ACS mosaic of M51 in BVI, and Halpha. While this is designed to produce a
lovely multi-color image of this photogenic target, its scientific return will
be limited for star formation studies. Hence we propose to augment these
observations by obtaining WFPC2 U band and NICMOS H band primary imaging (with
NICMOS Paschen alpha in parallel) of selected pointings of this interacting
galaxy system. At the modest cost of 14 additional orbits, we will: (1)
accurately determine the ages of the young star cluster population; (2) secure
the identification of 60-70 old globular clusters; (3) search for heavily dust
enshrouded stellar clusters; (4) investigate the distribution of the cluster
populations as a function of location (galactocentric, arms, interarms, etc.);
and (5) both remove the effects of dust and determine its properties. In
addition to our specific science goals, these observations lend themselves, on
their own or in synergy with data from GALEX and Spitzer, to a host of other
investigations, including those on evolved diffuse stellar populations,
galactic structure, and dust radiative transfer. We will thus release these
data early to the community, by relinquishing part of the proprietary period.
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Proposal Category: GO
Scientific Category: SOLAR SYSTEM
ID: 10502
Title: ACS Imaging of the Uranus Aurora and Hydrogen Corona
PI: John Clarke
PI Institution: Boston University
ACS SBC UV observations of Uranus are proposed with dual purposes that can be
achieved with a single set of observations. First, we propose to observe the
very unusual auroral of Uranus for the first time since IUE and Voyager in the
1980's. The Uranus aurora are centered on the magnetic poles, corresponding
to the 60 deg. tilted magnetic moment, closer to the equator than the
rotational poles. The brighter auroral emission appears around the weaker
magnetic pole. The auroral emissions are highly variable, as recorded with
IUE, and the rotational phase of Uranus is not known. The observations will
therefore cover the extent of a Uranus rotation (17.29 hours), and will be
repeated one-half solar rotation later to allow for variations in the solar
wind at Uranus. The high sensitivity of the ACS SBC at long wavelengths will
increase the sensitivity to auroral H2 emissions, and observations in cycle 14
near solar minimum will limit the sky background and reflected solar emissions
from the Uranus disc. Secondly, these images will measure the extended
hydrogen corona of Uranus, first seen by the Voyager 2 UVS. We propose to
model the distribution of the hydrogen corona to determine the source
processes in the Uranus upper atmosphere, by comparison with model runs from
an exospheric code.
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Proposal Category: GO
Scientific Category: STELLAR POPULATIONS
ID: 10503
Title: The Star Formation Histories of Early Type Dwarf Galaxies
in Low Density Environments: Clues from the Sculptor
Group
PI: Gary Da Costa
PI Institution: Australian National University
We seek HST ACS/WFC time to conduct a detailed study of the stellar
populations of 5 early-type (dE, dE/dIrr) dwarf galaxies in the nearby (~1.5
to 4 Mpc) Sculptor group. Four of these systems have been recently found to
contain modest amounts of HI, and existing ground-based and HST snapshot data
point to the potential presence of small populations of young (blue) stars in
at least three of these systems. Consequently, they resemble the Local Group
'transition' objects Phoenix and LGS3. The relative number of such transition
systems is thus substantially larger in the low density environment of the Scl
group than for the Local Group. Detailed stellar populations studies will
allow estimation of the star formation histories, via stellar population
modelling of the color-magnitude diagrams, of the target dwarfs, which in turn
will connect to gas consumption and retention rates. For the two nearer
dwarfs we aim to reach below the horizontal branch (a first for any system
beyond the Local Group) equivalent to a main sequence turnoff age of ~1 Gyr.
The observations of these two systems will also allow detection of RR Lyrae
variables and thus direct confirmation of the presence of old populations.
For the other three dwarfs will we cover the first 2.5 mags of the red giant
branch, equivalent to the main sequence termination for a ~300 Myr
population. The results will have implications for theories of galaxy
formation and evolution, particularly with regard to the evolutionary
relation between low luminosity dEs and dwarf irregulars.
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Proposal Category: GO
Scientific Category: GALAXIES
ID: 10504
Title: Characterizing the Sources Responsible for Cosmic
Reionization
PI: Richard Ellis
PI Institution: California Institute of Technology
Our group has demonstrated the role that massive clusters, acting as powerful
cosmic lenses, can play in constraining the abundance and properties of low-
luminosity star-forming sources beyond z~6; such sources are thought to be
responsible for ending cosmic reionization. The large magnification possible
in the critical regions of well-constrained clusters brings sources into view
that lie at or beyond the limits of conventional exposures such as the UDF, as
well as those in imaging surveys being undertaken with IRAC onboard Spitzer.
We have shown that the combination of HST and Spitzer is particularly
effective in delivering the physical properties of these distant sources,
constraining their mass, age and past star formation history. Indirectly, we
therefore gain a valuable glimpse to yet earlier epochs. Recognizing the
result (and limitations) of the UDF exposure, we propose a systematic search
through 6 lensing clusters with ACS and NICMOS for further z~6-7 sources in
conjunction with existing deep IRAC data. Our survey will mitigate cosmic
variance and extend the search both to lower luminosities and, by virtue of
the NICMOS/IRAC combination, to higher redshift. The goal is to count and
characterize representative sources at z~6-10 and to delineate the redshift
range of activity for the planning of future observations.
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Proposal Category: GO
Scientific Category: GALAXIES
ID: 10505
Title: The Onset of Star Formation in the Universe: Constraints
from Nearby Isolated Dwarf Galaxies.
PI: Carme Gallart
PI Institution: Instituto de Astrofisica de Canarias
The details of the early star formation histories of tiny dwarf galaxies can
shed light on the role in galaxy formation of the reionization which occured
at high redshift. Isolated dwarfs are ideal probes since their evolution is
not complicated by environmental effects owing to the vicinity of the Milky
Way and M31. In addition, dwarf galaxies are the most common type of galaxies,
and potentially the building blocks of larger galaxies. Since we can date the
oldest stars in them, their study represents a complementary approach to the
study of the formation and evolution of galaxies through high-z observations.
We propose to use the ACS to obtain a homogeneus dataset of high-quality
photometry, down to the old (13 Gyr) main-sequence turnoffs, for a
representative sample of 5 isolated Local Group dwarf galaxies. These data are
essential to unambiguously determine their early star formation histories,
through comparison with synthetic color-magnitude diagrams, and using the
constraints provided by their variable stars. Parallel WFPC2 observations of
their halos will allow us to reveal the actual nature of their stellar
population gradients, providing important aditional constraints on their
evolution. The proposed observations are being complemented with ground-based
spectroscopy, to obtain metallicity and kinematic information. The
observations requested here, which must reach M_I=+3.5 (I=27.5-28.2) with
S/N=10 in crowded systems, can only be achieved with HST using ACS, and won't
be possible with planned ground- or space-based facilities such as JWST. For
these reasons they were identified in the HST Treasury Workshop as key targets
for HST in its final years. Based on deep WFPC2 observations and ACS image
simulations, our team has designed an observational strategy which carefully
considers the optimal filter combination, the necessary photometry depth and
the effects of stellar crowding.
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Proposal Category: GO
Scientific Category: SOLAR SYSTEM
ID: 10506
Title: Coordinated observations of Saturn's auroral dynamic
morphology and Cassini plasma measurements
PI: Jean-Claude Gerard
PI Institution: Universite de Liege
Planetary FUV aurora is the most spectacular signature of the electrodynamical
coupling between the solar wind, the planet's magnetic field, and its
atmosphere. Saturn's magnetosphere has similarities both with the Earth's
magnetosphere, which is 'open' to solar wind interaction and Jupiter's
relatively 'closed' case with its large internal sources of plasma. HST
observations of Saturn's aurora have shown a much more complex and dynamic
morphology than anticipated: a frequent 'spiral' structure, a changing size
of the oval in response to variations of the solar wind dynamics pressure, and
large brightness changes in a few ten of minutes following compression of the
magnetosphere by the solar wind. In addition, the global morphology and some
spots move at 70% of the planetary co-rotation, while some other features
appear nearly fixed in local time. Recently, ideas have emerged to account for
Saturn's aurora specificities, although many aspects are still not understood
due to the paucity of observational data. Electric current models suggest that
the main oval is located at the limit between closed and open magnetic field
lines, near the magnetopause. The availability of Cassini in Saturn's magnetic
environment now offers a unique opportunity for collaborative science. We
thus propose to test the relationship between the aurora and conditions at
Saturn's magnetopause (MP) boundary. We plan to image the FUV aurora with ACS
at times of inbound Cassini crossing of the MP from the upstream solar
wind/magnetosheath region into the middle magnetosphere during an inbound
segment of a Cassini's orbit. FUV images will also reveal whether the main
oval changes its size over the interval, possibly indicating evidence for
changes in the amount of open flux in the system. These HST images of the
aurora simultaneous with in situ measurements of the plasma characteristics
and electrodynamics inside the magnetosphere are critical to obtain key
observational tests and constraints to future ideas and models of Saturn's
auroral precipitation and magnetospheric processes involved.
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Proposal Category: GO
Scientific Category: SOLAR SYSTEM
ID: 10507
Title: High resolution imaging of Jupiter's diffuse auroral
emissions inside and outside the main oval during solar
minimum.
PI: Denis Grodent
PI Institution: Universite de Liege
The analysis of HST-STIS FUV images has greatly and quickly advanced our
knowledge of the magnetospheric mechanisms producing the auroral emissions on
the giant planets. However, these studies were limited to the brightest
emissions and very little has been said about the fainter emissions, mainly
because of the lower S/N. We propose to image the faint auroral emissions on
Jupiter which could not be observed with STIS. We will take full advantage of
ACS/SBC's higher sensitivity to observe the diffuse auroral FUV emissions
appearing poleward and directly equatorward of Jupiter's main auroral oval in
the northern hemisphere. This proposal has the potential to reveal new
magnetosphere-ionosphere coupling mechanisms especially those involving solar
wind interactions with a giant planet.
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Proposal Category: GO
Scientific Category: SOLAR SYSTEM
ID: 10508
Title: Orbits, Masses, and Densities of Three Transneptunian
Binaries
PI: William Grundy
PI Institution: Lowell Observatory
The subset of transneptunian objects (TNOs) having natural satellites offers
unique opportunities for physical studies of these distant relics from the
outer parts of the protoplanetary nebula. HST/ACS is ideally suited to
determining orbits of TNO satellites, resulting in the system masses. In
conjunction with thermal emission observations by Spitzer, which provides
sizes, we can determine the densities of TNOs. Densities offer a powerful
window into their bulk compositions and interior structures.
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Proposal Category: GO
Scientific Category: COSMOLOGY
ID: 10509
Title: The Cluster Lens SDSS 1004+4112: Constraining World
Models With its Multiply-Imaged Quasar and Galaxies
PI: Christopher Kochanek
PI Institution: The Ohio State University Research Foundation
We will use deep ACS imaging of the giant (15 arcsec) four-image z_s=1.734
lensed quasar SDSS 1004+4112, and its z_l=0.68 lensing galaxy cluster, to
identify many additional multiply-imaged background galaxies. Combining the
existing single orbit ACS I-band image with ground based data, we have
definitely identified two multiply imaged galaxies with estimated redshifts of
2.6 and 4.3, about 15 probable images of background galaxies, and a point
source in the core of the central cD galaxy, which is likely to be the faint,
fifth image of the quasar. The new data will provide accurate photometric
redshifts, confirm that the candidate fifth image has the same spectral energy
distribution as the other quasar images, allow secure identification of
additional multiply-lensed galaxies for improving the mass model, and permit
identification of faint cluster members. Due to the high lens redshift and the
broad redshift distribution of the lensed background sources, we should be
able to use the source-redshift scaling of the Einstein radius that depends on
(d_ls/d_os), to derive a direct, geometric estimate of Omega_Lambda. The
deeper images will also allow a weak lensing analysis to extend the mass
distribution to larger radii. Unlike any other cluster lenses, the time delay
between the lensed quasar images (already measured for the A--B images, and
measurable for the others over the next few years), breaks the so-called
kappa-degeneracies that complicate weak-lensing analyses.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10510
Title: Morphology of massive early-type galaxies at z>1.2:
constraining galaxy formation models
PI: Marcella Longhetti
PI Institution: Osservatorio Astronomico di Brera, Milano
We ask for NICMOS-NIC2 H-band imaging of a sample of 10 massive early-type
galaxies spectroscopically identified at 1.26500A, would map the mass distribution of the bulk of their stellar
content. The targets have been revealed by our group on the basis of near-IR
spectroscopy obtained in the framework of a spectroscopic survey of a complete
sample of bright EROs (Ks<18.5). Optical and near-IR photometry is available
for all the targets, and low resolution near-IR spectra have allowed their
identification and redshift measurement. Spectroscopic and photometric data in
our hands show that they have already assembled stellar masses greater than 3
10^11 solar masses, and that the mean age of their stellar population is
estimated older than 2-3 Gyr for 6 of them and about 1 Gyr for the other 4
galaxies. Thus, they are among the most luminous and massive evolved galaxies
detected so far at z>1. Other data are needed to infer how they have
assembled such high stellar masses, i.e. to trace back their evolution. The
requested observations would allow us to reveal signs of past
interaction/merger event. A smooth r^{1/m} profile, coupled with no other
signs of interaction/merger (disturbed morphology), would place the possible
merger event of formation 1-2 Gyr before their redshift z \approx 1.5, i.e. at
z > 2-3. On the other hand, if signs of recent merger events will be found,
the last merger event forming the local massive spheroids will be constrained
at 1.5 < z < 2. Thus, the requested HST observations will allow for the first
time to see how massive early-type galaxies at z \approx 1.5 look like,
constraining in any case the redshift of the possible merging event of their
formation.
================================================================================
Proposal Category: GO
Scientific Category: STAR FORMATION
ID: 10511
Title: An Edge-on Disk around a Brown Dwarf?
PI: Kevin Luhman
PI Institution: Smithsonian Institution Astrophysical Observatory
We have recently discovered a young brown dwarf in the Taurus star-forming
region that exhibits several characteristics (very faint for its spectral
type, forbidden emission lines, anomalous near-IR colors) that are often
observed in stars occulted by edge-on circumstellar disks. We propose to
determine if an edge-on disk is indeed present by obtaining high-resolution
images of this brown dwarf with ACS/HRC on HST. If the disk is detected, we
will constrain its physical properties, particularly its diameter, by fitting
the images with the predictions of our models of brown dwarfs occulted by
circumstellar disks. These observations could potentially provide the first
direct measurement of the size of a disk around a brown dwarf, which would
comprise a fundamental test of models for the formation of these objects
(e.g., embryo ejection).
================================================================================
Proposal Category: SNAP
Scientific Category: SOLAR SYSTEM
ID: 10512
Title: Search for Binaries Among Faint Jupiter Trojan Asteroids
PI: William Merline
PI Institution: Southwest Research Institute
We propose an ambitious SNAPSHOT program to survey faint Jupiter Trojan
asteroids for binary companions. We target 150 objects, with the expectation
of acquiring data on about 50%. These objects span Vmag = 17.5-19.5, a range
inaccessible with ground-based adaptive optics. We now have a significant
sample from our survey of brighter Trojans to suggest that the binary fraction
is similar to that which we find among brighter main-belt asteroids, roughly
2%. However, our observations suggest a higher binary fraction for smaller
main-belt asteroids, probably the result of a different formation mechanism
(evident also from the physical characteristics of the binaries). Because the
collision environment among the Trojans is similar to that of the Main Belt,
while the composition is likely to be very different, sampling the binary
fraction among the fainter Trojans should help us understand the collisional
and binary formation mechanisms at work in various populations, including the
Kuiper Belt, and help us evaluate theories for the origin of the Trojans.
Calibration of and constraints on models of binary production and collisional
evolution can only be done using these large-scale, real-life physical systems
that we are beginning now to find and utilize.
================================================================================
Proposal Category: GO
Scientific Category: HOT STARS
ID: 10513
Title: The very late phases of a thermonuclear supernova
PI: Peter Milne
PI Institution: University of Arizona
A better understanding of the physics of Type Ia supernovae (SNe) is important
for their use as cosmological standard candles. Late time observations of the
SN light curves are poorly studied - but offers a unique way to probe the
explosion models. Combining state of the art models of 3-D explosions with
sophisticated spectral modeling, we can test these models against observations
in a way not earlier possible. In particular, the broad band light curves are
sensitive to the degree of clumping and the timing of the `infra-red
catastrophe', factors which depend on the explosion mechanism (deflagration
vs. delayed detonation). Further, these observations can probe the degree of
positron trapping in the ejecta, important for both the SN ejecta and for the
production of free positrons in the galaxy. Because of its small distance,
favorable galaxy location and excellent ground based follow-up - SN 2003hv
offers a unique opportunity to obtain the best late light curves to date.
Observations in several optical and IR bands will enable us to distinguish
between different model predictions.
================================================================================
Proposal Category: SNAP
Scientific Category: SOLAR SYSTEM
ID: 10514
Title: Kuiper Belt Binaries: Probes of Early Solar System
Evolution
PI: Keith Noll
PI Institution: Space Telescope Science Institute
Binaries in the Kuiper Belt are a scientific windfall: in them we have
relatively fragile test particles which can be used as tracers of the early
dynamical evolution of the outer Solar System. We propose a Snapshot program
using the ACS/HRC that has a potential discovery efficiency an order of
magnitude higher than the HST observations that have already discovered the
majority of known transneptunian binaries. By more than doubling the number
of observed objects in dynamically hot and cold subpopulations we will be
able to answer, with statistical significance, the question of whether these
groups differ in the abundance of binaries as a result of their particular
dynamical paths into the Kuiper Belt. Today's Kuiper Belt bears the imprints
of the final stages of giant-planet building and migration; binaries may offer
some of the best preserved evidence of that long-ago era.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10515
Title: The Unique Star Cluster System of M85
PI: Eric Peng
PI Institution: Dominion Astrophysical Observatory
Even with its long history as one of the pillars of modern astronomy, the
study of star clusters has continued to reveal new and surprising things.
Over the past decade, numerous programs with HST have shown that extragalactic
star clusters powerfully probe the processes of galactic formation, evolution,
and destruction. The diversity of star cluster systems is a testament to the
rich variation in galaxy properties. During the course of the ACS Virgo
Cluster Survey, we have discovered that the early-type galaxy M85 has a system
of star clusters unlike any other galaxy studied to date. Hundreds of star
clusters in M85 are fainter and more extended than typical globular clusters,
and have no local analog. We propose deep optical-infrared imaging with ACS
and NICMOS to obtain ages, metallicities, luminosities, and sizes of
unprecedented precision to characterize these new star clusters and unravel
the evolutionary state of M85 that gave rise to them.
================================================================================
Proposal Category: GO
Scientific Category: AGN/QUASARS
ID: 10516
Title: Host Galaxies of Reverberation-Mapped AGNs
PI: Bradley Peterson
PI Institution: The Ohio State University Research Foundation
We propose to obtain unsaturated ACS high-resolution images of four
reverberation-mapped active galactic nuclei in order to remove the point-like
nuclear light from each image, thus yielding a "nucleus-free" image of the
host galaxy. This will allow investigation of host galaxy properties: our
particular interest is determination of the host-galaxy starlight contribution
to the reverberation-mapping observations. This is necessary (1) for accurate
determination of the relationship between the AGN nuclear continuum flux and
the size of the broad Balmer-line emitting regions of AGNs, which is important
because this relationship is used in estimating black hole masses for large
samples of QSOs, and (2) for accurate determination of the bolometric
luminosity of the AGN proper. In a Cycle 12 SNAP program, we obtained images
of 14 of the 36 reverberation-mapped AGNs for this purpose. This additional
request is to complete this program through observations of the four important
remaining sources.
================================================================================
Proposal Category: GO
Scientific Category: COOL STARS
ID: 10517
Title: Imaging Astrometrically-Discovered Brown Dwarfs
PI: Steven Pravdo
PI Institution: Jet Propulsion Laboratory
We propose to image the astrometrically discovered companions of three M-
dwarfs with NICMOS to more tightly constrain their masses and determine their
stellar or sub-stellar natures. Each of these systems has been observed with a
sensitive ground-based adaptive optics system and no companions have been
detected. NICMOS results will eliminate an ambiguity in the astrometric mass
measurements that arises because a companion that contributes significantly to
the visible light reduces the motion of the center of light and mimics a small
motion of the center of mass. In addition the astrometric measurements made
with NICMOS will fix the scale of the system, distinguishing among possible
orbits. Finally the color photometry will constrain the spectral types to
within a couple of subtypes. When we measure the masses of astrophysical
objects, we test and assist the development of the theoretical mass models.
Models are based upon parameters such as age and metallicity. Determining the
correct mass thus deepens our understanding of the fundamental physics of
stars and substellar objects
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10518
Title: Dark matter and the missing images of cx2201-3201
PI: Paul Schechter
PI Institution: Massachusetts Institute of Technology
The galaxy lensing the z=3.9 quasar cx2201-3201 is a bulgeless edge-on spiral.
Models for the disk that contain more than 20% of the mass predict four
images, but only two are seen in ground-based images. We request 3 orbits to
obtain high resolution optical and infrared images. If the missing images are
indeed absent, more than 80% of the mass inside the Einstein radius must be in
an unseen spherical component.
================================================================================
Proposal Category: GO
Scientific Category: STAR FORMATION
ID: 10519
Title: Testing the Stellar Coalescence and Accretion Disk
Theories of Massive Star Formation with NICMOS
PI: Janet Simpson
PI Institution: NASA Ames Research Center
The importance of massive stars cannot be underestimated - they produce most
of the heavy elements in the universe and dominate the evolution of the
interstellar medium in their vicinity. In spite of their significance, our
understanding of their formation is meager. Both accretion through disks,
analogous to the process of low-mass star formation, and coalescence of low-
mass stars through collisions in the dense cores of stellar clusters have been
suggested. Possibly both mechanisms occur. High spatial resolution
polarization measurements of the closest massive young stellar objects (YSOs)
will enable us to search for evidence of disk accretion or coalescence in the
form of patterns indicative of light scattered off a coherent disk or off a
disk disrupted by an infalling star, respectively. Here we propose to use 2
micron polarimetry with NICMOS to identify the presence of accretion disks
around massive YSOs or to characterize their environments as possibly
disrupted from a close stellar encounter. There are only a few sources that
meet the stringent selection criteria for this investigation (even with HST),
which we will examine here. High spatial resolution is required, but even more
important, the point spread function (PSF) must be stable with time.
Furthermore, the PSF must put minimal flux into large spatial scales,
something that cannot be achieved with adaptive optics. This combination of
high Strehl ratio and stable PSF can only be achieved from space.
================================================================================
Proposal Category: GO
Scientific Category: STELLAR POPULATIONS
ID: 10520
Title: Resolving the Complex Star Formation History of the Leo I
Dwarf Spheroidal Galaxy
PI: Tammy Smecker-Hane
PI Institution: University of California - Irvine
Determining the star formation histories (SFHs) and chemical evolution of
nearby galaxies gives us powerful constrains on the physical processes that
regulate galaxy evolution. The SFHs can be measured most accurately by
comparing the observed densities of stars in color-magnitude diagrams (CMDs)
to predictions from stellar evolutionary models. WFPC2 imaging of the Leo I
dSph shows it is unique because its stellar population is relatively young.
Approximately 68% of its stars formed between 1 and 7 Gyr ago and only 12% of
its stars formed >~ 10 Gyr ago. We propose to vastly improve the derived SFH
of Leo I by exploiting ACS/WFC's higher quantum efficiency at bluer
wavelengths, higher spatial resolution, and larger field-of-view. The figure
of merit for our proposed observations, defined as the age resolution times
the number of stars detected, will be a factor of 12 higher than existing
WFPC2 observations. To surmount the degeneracy of age and metallicity in the
CMD, we have independently measured the metallicity distribution of its stars
using spectroscopy. Simultaneously modeling the metallicity distribution and
CMD, we will firmly constrain the evolution of the Leo I dSph, a unique
example of an isolated dwarf galaxy that has not been influenced by
interactions with the Milky Way or M31.
================================================================================
Proposal Category: GO
Scientific Category: AGN/QUASARS
ID: 10521
Title: ACS Imaging of a Unique Spitzer Field: Morphology of mid-
IR Variable Sources
PI: Jason Surace
PI Institution: California Institute of Technology
We propose to observe the IRAC Dark Field, an extragalactic field 15
arcminutes in diameter near the north ecliptic pole, using 50 orbits of ACS
imaging at I-band. This field is extraordinarily deep and is uniquely suited
to detecting variable objects in the mid-infrared. The high spatial resolution
ACS imaging will be used to derive morphological information about the
galaxies in the field, which will then be correlated with mid-infrared
variable objects (specifically AGN and supernovae) we have discovered. This
field is the dark current calibration target for the Spitzer Space Telescope,
the infrared counterpart to HST. Because the field is observed frequently as
part of routine operations, it is now similar in size and depth to the
infrared component of the GOODS program, and is confusion-limited in the mid-
infrared. More importantly, due to the periodicity of the observations, the
Spitzer observations are sensitive to variability on week timescales,
ultimately spanning a baseline of five years, and are the only mid-infrared
dataset that will ever have this capability at this depth. By complementing
our wide range of lower resolution imaging at optical and infrared
wavelengths, we hope to exploit one of HST's most unique capabilities -
unparalleled spatial resolution in the optical. While our specific interest
lies in analysis of variable sources, we will request no proprietary period on
the ACS data so that it may be used by the community to complement the
publicly available Spitzer data.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10522
Title: Calibrating Star Formation: The Link between Feedback and
Galaxy Evolution
PI: Daniela Calzetti
PI Institution: Space Telescope Science Institute
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 theoretical foundation of mechanical feedback is, to date, unconstrained
by observations. We propose to investigate this fundamental aspect of star
formation on a sample of three local actively star-forming galaxies, He2-10,
NGC4449, and Holmberg II. The three galaxies have been selected to occupy an
unexplored, yet crucial for quantifying mechanical feedback, niche in the two-
parameter space of star formation intensity and galaxy mass. ACS/WFC and WFPC2
narrow-band observations in the light of H-beta, [OIII], H-alpha, and [NII]
will be obtained for all three galaxies, in order to: (1) discriminate the
feedback-induced shock fronts from the photoionization regions; (2) map the
shocks inside and around the starburst regions; and (3) measure the energy
budget of the star-formation-produced shocks. These observations,
complemented by existing data, will yield: (1) the efficiency of the
feedback, i.e. the fraction of the star formation's mechanical energy that is
transported out of the starburst volume rather than confined or radiated away;
(2) the dependence of this efficiency on the two fundamental parameters of
star formation intensity and stellar mass. The high angular resolution of HST
is crucial for separating the spatially narrow shock fronts (~5 pc, ~0.25" at
4 Mpc) from the more extended photoionization fronts. The legacy from this
project will be the most complete quantitative measurement of the energetics
associated with feedback processes. We will secure the first milestone for
placing feedback mechanisms on a solid physical ground, and for understanding
quantitatively their role on the energetics, structure, and star formation
history of galaxies at all redshifts.
================================================================================
Proposal Category: SNAP
Scientific Category: GALAXIES
ID: 10523
Title: The Halo Shape and Metallicity of Massive Spiral Galaxies
PI: Roelof de Jong
PI Institution: Space Telescope Science Institute
We propose to resolve the stellar populations of the halos of seven nearby,
massive disk galaxies using a SNAP survey with WFC/ACS. These observations
will provide star counts and color-magnitude diagrams 2-3 magnitudes below the
tip of the Red Giant Branch along the two principal axes and one intermediate
axis of each galaxy. We will measure the metallicity distribution functions
and stellar density profiles from star counts down to very low average surface
brightnesses, equivalent to ~31 V-mag per square arcsec. This proposal will
create a unique sampling of galaxy halo properties, as our targets cover a
range in galaxy mass, luminosity, inclination, and morphology. As function of
these galaxy properties this survey will provide: - the first systematic
measurement of radial light profiles and axial ratios of the diffuse
stellar halos and outer disks of spiral galaxies - a comprehensive analysis
of halo metallicity distributions as function of galaxy type and position
within the galaxy - an unprecedented study of the stellar metallicity and
age distribution in the outer disk regions where the disk truncations
occur - the first comparative study of globular clusters and their field
stellar populations We will use these fossil records of the galaxy
assembly process to test halo formation models within the hierarchical galaxy
formation scheme.
================================================================================
Proposal Category: GO
Scientific Category: STELLAR POPULATIONS
ID: 10524
Title: Blue Stragglers: a key stellar population to probe
internal cluster dynamics
PI: Francesco R. Ferraro
PI Institution: Universita degli Studi di Bologna, Italy
This proposal is part of a coordinated project devoted to understand the
interplay of globular cluster (GC) dynamics and the formation and evolution of
blue straggler stars (BSS). By using a combination of HST and ground-based
observations we are constructing complete BSS surveys in a sample of GCs;
complete BSS surveys require mid-UV HST observations in the center and wide
field CCD ground based observations under excellent seeing conditions of the
exterior. Up to now only four clusters have been surveyed in this way and the
results are surprising: in three GCs (M3, 47 Tuc, NGC 6752) we have discovered
that the BSS radial distribution is bimodal, highly peaked in the cluster
center, rapidly decreasing at intermediate radii and rising again at large
radii (Ferraro et al. 1997, 2004, Sabbi et al. 2004), conversely BSS
population in Omega Centauri does not show any signature of the segregation
which would be expected for a class of objects arising from either stellar
interactions or binarity (Ferraro et al. 2005). These observational facts are
opening a new prospective in the study of the formation processes and
evolution of BSS in GCs. By using extensive simulations, we demonstrated that
the spatial distribution of BSS observed in 47 Tuc can be only reproduced if a
sizable fraction of BSS is generated (via mass transfer in primordial
binaries) in the peripheral region of the cluster (Mapelli et al 2004), thus
excluding a purely collisional formation scenario. Here we propose mid-UV
imaging of a few clusters suspected of harboring a large population of central
BSS and a few known to have many BSS the external region. These are good
candidates for determining accurate BSS radial distributions. The modest
amount of time proposed here will go far to determine the ubiquity of BSS
bimodality and to constrain models of dynamical evolution. Since we believe
the proposed observations would be useful to the entire stellar community (for
multifold purposes) we waive the propretary period.
================================================================================
Proposal Category: SNAP
Scientific Category: COOL STARS
ID: 10525
Title: Characterizing the Near-UV Environment of M Dwarfs:
Implications for Extrasolar Planetary Searches and
Astrobiology
PI: Suzanne Hawley
PI Institution: University of Washington
We propose SNAP observations with the ACS HRC PR200L prism, designed to
measure the near ultraviolet emission in a sample of 107 nearby M dwarfs. The
sample spans the mass range from 0.1 - 0.6 solar masses (temperature range
2200K - 4000K) where the UV energy distributions vary widely between active
and inactive stars. The strength and distribution of this UV emission can have
critical consequences for the atmospheres of attendant planets. Our proposed
observations will provide desperately needed constraints on models of the
habitability zone and the atmospheres of possible terrestrial planets orbiting
M dwarf hosts, and will be used to sharpen TPF target selection. In addition,
the NUV data will be used in conjunction with existing optical, FUV and X-ray
data to constrain a new generation of M dwarf atmospheric models, and to
explore unanswered questions regarding the dynamo generation and magnetic
heating in these low-mass stars.
================================================================================
Proposal Category: GO
Scientific Category: ISM AND CIRCUMSTELLAR MATTER
ID: 10526
Title: Dynamics of the Polarization Structure of the Crab Nebula
PI: J. Hester
PI Institution: Arizona State University
The Crab Nebula is not a free expansion SNR. Rather, it is a pulsar wind
nebula expanding from the inside out into a larger remnant of freely expanding
ejecta. At the heart of this object is the Crab Pulsar and the region where
the pulsar's highly nonisotropic wind interacts with the larger synchtron
nebula. HST and Chandra monitoring has shown this to be one of the most
intricately structured and highly dynamical objects ever observed. In Cycle
12 we demonstrated our ability to use the polarization capabilities of the ACS
to isolate physically discrete features within the Crab Synchrotron Nebula and
accurately measure their polarization characteristics. These data provide a
unique look at the physical structure in the heart of the Crab, adding a new
dimension to past observations. Polarization provides extensive information
about field geometries, the degree of disorder in the field, and particle
pitch angle distributions. But one image of the Crab is like a single image of
waves at the beach. It necessarily misses the point. In the Crab, the name
of the game is "dynamics". In this proposal we request time to monitor
changes in the polarization structure of the Crab. This program will allow us
to follow the changing polarization of features including relativistically
moving wisps in the Crab Nebula. This is the only place in the sky where a
dynamic relativistic plasma can be observed in sufficient detail to make such
measurements possible, and the HST/ACS is the only instrument that we are
likely to see in our careers capable of making the measurement. These
observations will be an important addition to the already rich observational
legacy of HST for what is arguably the most important single object in
astrophysics.
================================================================================
Proposal Category: GO
Scientific Category: ISM AND CIRCUMSTELLAR MATTER
ID: 10527
Title: Imaging Scattered Light from Debris Disks Discovered by
the Spitzer Space Telescope Around 20 Sun-like Stars
PI: Dean Hines
PI Institution: Space Science Institute
We propose to use the high contrast capability of the NICMOS coronagraph to
image a sample of newly discovered circumstellar disks associated with sun-
like stars. These systems were identified by their strong thermal infrared
emission with the Spitzer Space Telescope as part of the Spitzer Legacy
Science program titled, "The Formation and Evolution of Planetary Systems
(FEPS)." Modelling of the thermal excess emission in the form of spectral
energy distributions alone cannot distinguish between narrowly confined high
opacity disks and broadly distributed, low opacity disks. However, our
proposed NICMOS observations can, by imaging the light scattered from this
material. Even non-detections will place severe constraints on the disk
geometry, ruling out models with high optical depth. Unlike previous disk
imaging programs, our program contains a well defined sample of solar mass
stars covering a range of ages from ~10Myrs to a few Gyrs, allowing us to
study the evolution of disks from primordial to debris for the first time.
These results will greatly improve our understanding of debris disks around
Sun-like stars at stellar ages nearly 10x older than any previous
investigation. Thus we will have fit a crucial piece into the puzzle
concerning the formation and evolution of our own solar system.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10528
Title: Ram Pressure Stripping and Dense Cloud Ablation in the
Virgo Spiral NGC 4402
PI: Jeffrey Kenney
PI Institution: Yale University
We propose to image in BVI with HST ACS the highly inclined Virgo cluster
spiral galaxy NGC 4402, which is an outstanding example of a galaxy undergoing
stripping of its ISM by an ICM-ISM interaction. Ground-based images at 0.5"
resolution appear to show active dust stripping, triggered star formation, and
ablation of dense molecular clouds by the ICM wind. The near side of NGC 4402
contains the leading edge of interaction, giving us a relatively unobscured
view of the processes which occur as the ICM wind impacts the ISM. High
resolution HST B-I images of dust in NGC 4402 can reveal the fate of giant
molecular clouds during a stripping event, including whether clouds above some
size get left behind as the rest of the ISM is stripped from around them, how
decoupled clouds become ablated by the ICM wind, and how the survival time
varies with cloud mass. We will identify and estimate the ages of stars and
star clusters in the stripped outer disk and halo, and from the spatial
distributions of the younger objects, constrain the stripping history of the
galaxy. Its proximity, orientation, stage of evolution, and direction of
travel through the ICM make NGC 4402 an outstanding subject for a detailed HST
study of ICM-ISM stripping. An in-depth study of this galaxy will provide new
insight into the physical processes of ISM-ICM interactions and give us
greater understanding of cluster galaxy evolution, both in Virgo and at higher
redshifts.
================================================================================
Proposal Category: GO
Scientific Category: STELLAR POPULATIONS
ID: 10529
Title: A Deep H-band Probe of the Globular Cluster Mass function
PI: Arunav Kundu
PI Institution: Michigan State University
We propose to obtain deep NICMOS H-band data for the globular clusters in the
inner region of M87 and coordinated parallel ACS WFC g and z band observations
of a second field which has very deep archival NICMOS data. Therefore, our
proposed deep NICMOS observation overlaps corresponding deep archival optical
data in the inner regions, and the parallel ACS observations overlap deep
NICMOS images in the outer field. The combination of the sensitivity of the
near infrared to the mass of old stellar systems such as the globular clusters
in M87 and the ability of the optical to isolate the metal-rich and metal-poor
subcomponents of the globular cluster system will allow us to probe the mass
function, and the possible variation with metallicity, to unprecedented
depths. These observations are critical to linking the commonly observed
cluster luminosity function to the usually derived mass function in
theoretical calculations of globular cluster and globular cluster system
formation and evolution models. The multiple pointings will allow us to probe
the radial variations in globular cluster properties and test the predictions
of cluster formation and dynamical destruction models. Because of its
extremely rich globular cluster system (~15,000 clusters) M87 is one of the
only galaxies in which such a study can be conducted with a statistically
significant number of candidate clusters (approximately 300 globular clusters
in this study) with efficient use of HST time.
================================================================================
Proposal Category: GO
Scientific Category: COSMOLOGY
ID: 10530
Title: Probing Evolution And Reionization Spectroscopically
(PEARS)
PI: Sangeeta Malhotra
PI Institution: Space Telescope Science Institute
While imaging with HST has gone deep enough to probe the highest redshifts,
e.g. the GOODS survey and the Ultra Deep Field, spectroscopic identifications
have not kept up. We propose an ACS grism survey to get slitless spectra of
all sources in a wide survey region (8 ACS fields) up to z =27.0 magnitude,
and an ultradeep field in the HUDF reaching sources up to z =28 magnitude. The
PEARS survey will: (1) Find and spectrocopically confirm all galaxies between
z=4-7. (2) Probe the reionization epoch by robustly determining the luminosity
function of galaxies and low luminosity AGNs at z = 4 - 6. With known
redshifts, we can get a local measure of star formation and ionization rate in
case reionization is inhomogeneous. (3) Study galaxy formation and evolution
by finding galaxies in a contiguous redshift range between 4 < z < 7, and
black hole evolution through a census of low-luminosity AGNs. (4) Get a
robust census of galaxies with old stellar populations at 1 < z < 2.5,
invaluable for checking consistency with heirarchical models of galaxy
formation. Fitting these galaxies' spectra will yield age and metallicity
estimates. (5) Study star-formation and galaxy assembly at its peak at 1< z <
2 by identifying emission lines in star-forming galaxies, old populations
showing the 4000A break, and any combination of the two. (6) Constrain faint
white dwarfs in the Galactic halo and thus measure their contribution to the
dark matter halo. (7) Derive spectro-photometric redshifts by using the grism
spectra along with broadband data. This will be the deepest unbiased
spectroscopy yet, and will enhance the value of the multiwavelength data in
UDF and the GOODS fields to the astronomical community. To this end we will
deliver reduced spectra to the HST archives.
================================================================================
Proposal Category: GO
Scientific Category: COSMOLOGY
ID: 10531
Title: The most distant X-ray cluster at z = 1.4: morphologies,
color-magnitude relation and Fundamental Plane
PI: Chris Mullis
PI Institution: University of Michigan
We have been engaged in a serendipitous search for very distant clusters based
on extended X-ray sources in archival XMM-Newton observations, followed up by
R and z snapshot imaging with VLT-FORS2. Very recent VLT-FORS2 spectroscopy
of the best high-z candidate (reddest R-z galaxy overdensity) has
unambiguously confirmed the presence of a massive cluster at z = 1.392 (11
secure redshifts), a record-breaking distance to date, which bears a crucial
leverage on the evolution and formation of the most massive galaxies and
clusters. We propose here to obtain deep NICMOS images in the H band and ACS
images in the z band of the z = 1.4 cluster. The high resolution and
sensitivity will allow us to study morphologies, measure lengthscales and
surface photometry of the cluster members. We will analyse the color-
magnitude relation and, in combination with velocity dispersions from VLT-
FORS2 spectroscopy, we will extend the study of the Fundamental Plane to the
highest possible limit. Tracing these scaling relations in clusters to an
unprecedented look-back time will enable us to put strong constraints on the
formation epoch of cluster galaxies.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10532
Title: Kinematics and morphology of the most massive field disk
galaxies at z>1
PI: Kai Noeske
PI Institution: University of California - Santa Cruz
We propose to obtain 1 orbit NIC-2 images of a sample of the 15 most massive
galaxies found at $1 < z < 1.3$. These were culled from over 20,000 Keck
spectra collected as part of DEEP and are unique among high redshift massive
galaxy samples in being kinematically selected. We intend to test whether
these potentially very young galaxies are likely precursors to massive local
disks, assuming no further merging. NIC-2 images provide rest-frame optical
morphologies that will show whether they are normal disky systems or instead
more disturbed looking objects with multiple subcomponents, mergers, peculiar
structure, etc. NIC-2 provides near-IR resolutions sufficient to enable
measurements of bulges and disks subcomponents. The near-IR will fill a
critical gap in the broad-band SED photometry of the galaxy and its
subcomponents to estimate mean stellar ages and stellar masses and to assess
whether old stellar bulges and disks are in place at that time. Finally, this
sample will yield the first statistically significant results on the $z > 1$
evolution of the Tully-Fisher relation for massive galaxies.
================================================================================
Proposal Category: GO
Scientific Category: STAR FORMATION
ID: 10533
Title: The IMF in NGC6611: the environmental influence on the
formation of low-mass stars and brown dwarfs
PI: Joana Oliveira
PI Institution: University of Keele
We propose to use HST with ACS and NICMOS to survey the central area of the
young (2 Myr) cluster NGC6611 in the Eagle Nebula, with the goal of
constructing the low-mass and substellar Initial Mass Function (IMF). We plan
to obtain deep images in I (F775W) and Z (F850LP) with ACS/WFC, and deep
images in J (F110W) and H (F160W) for 25 NICMOS/NIC2 fields within the 202" x
202" ACS/WFC field. Using a proven technique based on the use of IZJH color-
magnitude and color-color diagrams to identify and determine the masses of the
low-mass pre-main sequence cluster members, we are thus able to construct the
IMF down to masses of 0.02-0.03 Msun. With an intense ionizing radiation field
but a relatively low density, NGC6611 provides a unique laboratory in which to
test the importance of photoevaporation and density on the formation of low-
mass stars and brown dwarfs, through comparison with the IMFs determined for
the different environments in the Orion Nebular Cluster, Taurus and IC348.
This will not only offer substantial new insight into the physics of star
formation, but also have important ramifications for estimating the global
star formation rates at high redshift, the efficiency of galactic chemical
evolution and the contribution of sub-stellar mass objects to the baryonic
dark matter content of the Universe.
================================================================================
Proposal Category: SNAP
Scientific Category: SOLAR SYSTEM
ID: 10534
Title: 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, months, and years. Uranus is
rapidly approaching equinox in 2007, with another 4 degrees of latitude
becoming visible every year. Recent HST observations during this epoch
(including 6818: Hammel, Lockwood, and Rages; 8680: Hammel, Rages, Lockwood,
and Marley; 8634: Rages, Hammel, Lockwood, Marley, and McKay; and 10170:
Rages, Hammel, Lockwood, and Marley) have revealed strongly wavelength-
dependent latitudinal structure and the presence of numerous visible-
wavelength cloud features in the northern hemisphere. Long-term ground-based
observations (Lockwood and Thompson 1999) show seasonal brightness changes
whose origins are not well understood. Recent near-IR images of Neptune
obtained using adaptive optics on the Keck Telesccope together with images
from our Cycle 9 Snapshot program (8634) show a general increase in activity
at south temperate latitudes as well as the possible development of another
Great Dark Spot. 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: HOT STARS
ID: 10535
Title: High Temperature Accretion Flows and Reprocessing in X-
ray Binaries: The ADC Source 4U 1822-371
PI: Edward Robinson
PI Institution: University of Texas at Austin
The eclipsing low-mass X-ray binary 4U 1822-371 is the ideal system in which
to observe hot accretion and the effects of strong irradiation. Its orbital
period is 5.57~hr and its orbital inclination is high enough that flux from
the neutron star is blocked by the edge-on accretion disk in the system.
Because the neutron star is hidden its Accretion Disk Corona is visible.
These ADCs are present in most if not all low-mass X-ray binaries but are
generally not visible. 4U 1822-371 provides a unique opportunity to study an
ADC and disk irradiation because the eclipse by the secondary star allows
their geometry and flux to be mapped. We will perform a multiwavelength light
curve synthesis and eclipse analysis of 4U 1822-371. The scientific goal is
to map the geometry and flux from its ADC and from its irradiated accretion
disk. The crucial and irreplaceable role of HST is to provide the UV data
needed to disentangle the ADC from the irradiated accretion disk. We will
obtain time-resolved, objective-prism UV spectroscopy of 4U 1822-371 using the
ACS/SBC with the PR130L prism covering most of its orbit and all of the
eclipse. This combination will yield excellent orbital light curves in the UV
continuum and in the integrated line fluxes.
================================================================================
Proposal Category: SNAP
Scientific Category: COOL STARS
ID: 10536
Title: What Are Stalled Preplanetary Nebulae? An ACS SNAPshot
Survey
PI: Raghvendra Sahai
PI Institution: Jet Propulsion Laboratory
Essentially all planetary nebulae (PNs) are aspherical, whereas the mass-loss
envelopes of AGB stars are strikingly spherical. Our previous SNAPshot surveys
of a morphologically unbiased sample of pre-planetary nebulae (PPNs) --
objects in transition between the AGB and PN evolutionary phases -- show that
roughly half our observed targets are resolved, with bipolar or multipolar
morphologies. Spectroscopic observations of our sample confirm that these
objects have not yet evolved into planetary nebulae. Thus, the transformation
from spherical to aspherical geometries has already fully developed by the
time these dying stars have become PPNs. Although our current studies have
yielded exciting results, they are limited in two important ways -- (1) the
number of well-resolved objects is still small (18), and the variety of
morphologies observed relatively multitudinous, hence no clear trends can yet
be established between morphology and other source properties (e.g., near-IR,
far-IR colors, stellar spectral type, envelope mass), and (2) the current
samples are strongly biased towards small PPNs, as inferred from their low 60-
to-25 micron flux ratios [R(60/25)<1]. However, the prototype of objects with
R(60/25)>1, the Frosty Leo Nebula, has a puzzlingly large post-AGB age (almost
10^4 yr) and a fairly cool central star, very different from the expectations
of single-star stellar evolutionary models. A proposed, but still speculative,
hypothesis for such objects is that the slow evolution of the central star is
due to backflow of material onto the mass-losing star, retarding its evolution
towards the PN phase. This hypothesis has significant consequences for both
stellar and nebular evolution. We therefore propose a survey of PPNs with
R(60/25)>1 which is heavily weighted towards the discovery of such "stalled
PPNs". Supporting kinematic observations using long-slit optical spectroscopy
(with the Keck), millimeter and radio interferometric observations (with OVRO,
VLA & VLBA) are being undertaken. The results from this survey (together with
our previous work) will allow us to draw general conclusions about the complex
mass-outflow processes affecting late stellar evolution, and will provide
crucial input for theories of post-AGB stellar evolution. Our survey will
produce an archival legacy of long-standing value for future studies of dying
stars.
================================================================================
Proposal Category: GO
Scientific Category: COOL STARS
ID: 10537
Title: Caught in the Act with HST -- Active Jet Sculpting in the
Young Preplanetary Nebulae IRAS 22036+5306
PI: Raghvendra Sahai
PI Institution: Jet Propulsion Laboratory
We have discovered an extended, highly-structured and bipolar nebula
surrounding the post-AGB object IRAS22036+5306 (I22036), in a Cycle 10 WFPC2
imaging survey of very young pre-planetary nebulae (PPNs). Young PPNs like
I22036, objects in rapid transition between the AGB and Planetary Nebulae (PN)
phases, retain direct signatures, in the spatial character of their outflows,
of the physical mechanisms which transform slowly expanding, round
circumstellar AGB envelopes into highly aspherical PNs with fast-expanding
elongated lobes along one or more axes. I22036 shows intriguing evidence for
the presence of jets in the HST images, and VLA A-array maps show OH maser
emission in a linear structure along the nebular axis. Our ground-based
echelle H-alpha spectra show high-velocity blue-shifted absorption in a very
broad (~2000 km/s) line profile, and mm-wave CO J=1-0 interferometric data
show a bipolar molecular outflow. There are very few young PPNs like I22036
which show clear morphological & kinematical evidence of the presence of jets
and their working surfaces, making it unquestionably a key object for
understanding how jets can sculpt out bipolar lobes in a progenitor AGB star
wind. Using ground-based long-slit spectroscopy with the Keck/ESI, we have
partially spatially resolved the H-alpha emission in this object. We now
propose to image I22036 in F658N, F631N, F606W and F814W in order to identify
accurately the location and structure of the shocked gas, and its relation to
the jets and their working surfaces. An important goal is to determine whether
we can characterise the forward and reverse shocks near the heads of the
knotty jets. The proposed HST imaging will help us to understand the spatio-
kinematic structure of the outflowing gas in the bipolar lobes, and allow us
to study the relationships between the important dynamical components of this
nebula. Supporting ground-based observations such as Zeeman measurements of
polarised OH masers with the VLBA to search for magnetic fields in I22036 are
being pursued for testing magnetic-collimation models for jets in PPNs.
================================================================================
Proposal Category: GO
Scientific Category: STAR FORMATION
ID: 10538
Title: Near-IR Spectrophotometry of 2MASSWJ 1207334-393254B - An
Extra-Solar Planetary Mass Companion to a Young Brown
Dwarf
PI: Glenn Schneider
PI Institution: University of Arizona
We propose to obtain "short" wavelength near-IR diagnostic and characterizing
spectra of the very high probability candidate extra-solar giant planet (EGP)
companion to 2MASSWJ 1207334-393254 (2M1207), a young brown dwarf and TW
Hydrae Association member. Recent NICMOS camera 1 multi-band photometric
imaging of the companion candidate, 0.77" (54 AU projected) from 2M1207 -
initially detected at longer wavelengths with VLT/NACO - implicate an object
of several Jupiter masses based on cooling models of EGPs and the likely age
of 2M1207 (~ 8 Myr). Physical companionship of the EGP candidate with 2M1207
has been established at the 99.1% level of confidence via second-epoch NICMOS
astrometric observations. Diagnostic spectra in the 0.8 to 1.9 micron region
(unobtainable from the ground and overlapping the NICMOS imaging observations)
will (a) critically inform on the physical nature of the EGP, (b) provide
currently non-existing information to test/constrain theoretical models of EGP
properties and evolution, and (c) unequivocally confirm the imaging of a bone
fide EGP. Background light from 2M1207 would normally swamp the EGP spectrum
with direct spectral imaging. To obviate this, we propose PSF-subtracted grism
spectra of the EGP using 2M1207 as its own spectral template via two-
orientation high-contrast image subtraction. The temporal stability of the
HST+NICMOS PSF enables self-subtractions of targets at different field
orientations resulting in contrast enhancements of 5 to 6 stellar magnitudes
in the circumstellar background at ~ 0.8" at these wavelengths. With the grism
field oriented to place the EGP "above" and "below" 2M1207 (at two
observational epochs) two independent spectra of the EGP will emerge from a
difference image. This prototypical spectrum will serve to test and improve
upon current models of young EGPs which predict flux suppression by molecular
absorption in their atmospheres.
================================================================================
Proposal Category: GO
Scientific Category: ISM AND CIRCUMSTELLAR MATTER
ID: 10539
Title: Coronagraphic Imaging of Bright New Spitzer Debris Disks
PI: Karl Stapelfeldt
PI Institution: Jet Propulsion Laboratory
Fifteen percent of bright main sequence stars possess dusty circumstellar
debris disks revealed by far-infrared photometry. These disks are signposts
of planetary systems: collisions among larger, unseen parent bodies maintain
the observed dust population against losses to radiation pressure and P-R
drag. Images of debris disks at optical, infrared, and millimeter wavelengths
have shown central holes, rings, radial gaps, warps, and azimuthal asymmetries
which indicate the presence of planetary mass perturbers. Such images provide
unique insights into the structure and dynamics of exoplanetary systems.
Relatively few debris disks have been spatially resolved. Only nine have ever
been resolved at any wavelength, and at wavelengths < 10 microns (where
subarcsec resolution is available), only seven: beta Pictoris, HR 4796, HD
141569, AU Mic, HD 107146, HD 92945, and Fomalhaut. Imaging of many other
debris disk targets has been attempted with various HST cameras/coronagraphs
and adaptive optics, but without success. The key property which renders a
debris disk observable in scattered light is its dust optical depth. The
seven disks imaged so far all have a dust excess luminosity >~ 0.01% that of
the central star; no disks with smaller optical depths have been detected.
Most main sequence stars known to meet this requirement have already been
observed, so future progress in debris disk imaging depends on discovering
additional stars with large infrared excess. The Spitzer Space Telescope
offers the best opportunity in 20 years to identify new examples of high
optical depth debris disk systems. We propose ACS coronagraphic imaging of
nine bright, new debris disks uncovered during the first year of the Spitzer
mission. Our goal is to obtain the first resolved images of these disks at ~3
AU resolution,define the disk sizes and orientations,and uncover disk
substructures indicative of planetary perturbations. The results should double
the number of debris disks observed at 0.06" resolution, and open a wider
window into the structure of planetary systems.
================================================================================
Proposal Category: GO
Scientific Category: STAR FORMATION
ID: 10540
Title: Imaging Nearby Dusty Disks
PI: Alycia Weinberger
PI Institution: Carnegie Institution of Washington
Images of circumstellar debris disks around young stars display complex
structures that suggest they harbor forming planets. Disks around stars of
nearly the same age and mass show dramatically different morphologies
including rings with brightness asymmetries and multiple warps. The reasons
for this heterogeneity are not understood, nor given the small sample of
imaged disks, can we be sure we have yet observed all possible outcomes of the
planet formation process. Disk imaging programs have demonstrated that the
Hubble Space Telescope is the only excellent platform for the high-contrast
detection of scattered light disks in the presence of their bright parent
stars. Therefore, we propose a NICMOS imaging survey of the nearest,
youngest, stars to Earth with substantial disks known from infrared excess
emission.
================================================================================
Proposal Category: GO
Scientific Category: AGN/QUASARS
ID: 10541
Title: Probing the jet mattter content of quasar PKS 0637-752
PI: Markos Georganopoulos
PI Institution: University of Maryland Baltimore County
The matter content (electron-proton vs electron-positron composition) of
extragalactic jets remains unknown, despite over three decades of work. Here,
we propose NICMOS/NIC3 and ACS observations of the Chandra-detected, one sided
jet of the superluminal quasar PKS 0637-752 to derive the jet matter content
by measuring the component of the Cosmic Microwave Background (CMB) radiation
that is bulk-Comptonized (BC) by the cold electrons in the relativistically
flowing large scale jet. What makes this source particularly suited for this
procedure, is the absence of significant non-thermal jet emission from the
'bridge', the region between the core and the first bright knot WK7.8,
guaranteeing that most of the electrons in the bridge are cold, leaving the
BC scattered CMB radiation as the only significant source of photons in this
region. The proposed NICMOS and ACS observations of the knot WK7.8 will
provide spectral information in the IR-UV regime, which, together with
existing multiwavelength data, will be used to derive the jet Doppler factor
and minimum power necessary to power the knot emission as a function of the
jet matter content. These will in turn be used to deduce, or strongly
constrain, the actual jet matter content through comparison with the
proposed NICMOS observations of the BC 'bridge' emission.
================================================================================
Proposal Category: GO
Scientific Category: STELLAR POPULATIONS
ID: 10542
Title: Charting the Sparkling Star Formation in NGC346
PI: Antonella Nota
PI Institution: Space Telescope Science Institute - ESA
New, stunning V, I images of the youngest and most massive star forming
region NGC 346, in the Small Magellanic Cloud, have been recently obtained
with the HST/ACS. They reveal a myriad of small compact clusters: some are
still embedded in dust, possibly connected by gas and dust filaments. We
also discover a rich population of pre-main sequence low mass stars (~3 -
0.6 Mo) mainly distributed in the body of NGC 346 and in these compact
clusters, which formed with the central cluster (~5My ago), but have not
reached the main sequence yet. The immediate question that emerges is: how
did star formation occur in this region? Is there evidence for an age spread
among these clusters, that could be indicative of sequential star formation?
We are, therefore, requesting an immediate follow up investigation with the
ACS/HRC to perform a comprehensive UV/U study of the ten largest clusters
identified in the NGC 346 region, with the objective of determining, in
combination with the already available deep V,I data, their mass function,
their upper mass cut-off, whether mass segregation is present, whether there
are age variations, and what is the impact of the stellar feedback, with the
final aim to establish how star formation has occured and progressed in this
low metallicity environment.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10543
Title: Microlensing in M87 and the Virgo Cluster
PI: Edward Baltz
PI Institution: Stanford University
Resolving the nature of dark matter is an urgent problem. The results of the
MACHO survey of the Milky Way dark halo toward the LMC indicate that a
significant fraction of the halo consists of stellar mass objects. The
VATT/Columbia survey of M31 finds a similar lens fraction in the M31 dark
halo. We propose a series of observations with ACS that will provide the most
thorough search for microlensing toward M87, the central elliptical galaxy of
the Virgo cluster. This program is optimized for lenses in the mass range
from 0.01 to 1.0 solar masses. By comparing with archival data, we can detect
lenses as massive as 100 solar masses, such as the remnants of the first
stars. These observations will have at least 15 times more sensitivity to
microlensing than any previous survey, e.g. using WFPC2. This is due to the
factor of 2 larger area, factor of more than 4 more sensitivity in the I-band,
superior pixel scale and longer baseline of observations. Based on the halo
microlensing results in the Milky Way and M31, we might expect that galaxy
collisions and stripping would populate the overall cluster halo with a large
number of stellar mass objects. This program would determine definitively if
such objects compose the cluster dark matter at the level seen in the Milky
Way. A negative result would indicate that such objects do not populate the
intracluster medium, and may indicate that galaxy harassment is not as
vigorous as expected. We can measure the level of events due to the M87 halo:
this would be the best exploration to date of such a lens population in an
elliptical galaxy. Star-star lensing should also be detectable. About 20
erupting classical novae will be seen, allowing to determine the definitive
nova rate for this giant elliptical galaxy. We will determine if our recent
HST detection of an M87 globular cluster nova was a fluke, or indicative of a
100x higher rate of incidence of cataclysmic variables and nova eruptions in
globulars than previously believed. We will examine the populations of
variable stars, and will be able to cleanly separate them from microlensing.
================================================================================
Proposal Category: GO
Scientific Category: STELLAR POPULATIONS
ID: 10544
Title: Resovled Images of LMC Microlensing Events Observed by a
Telescope at 2 AU from Earth
PI: David Bennett
PI Institution: University of Notre Dame
The identity of the lens objects for most of the LMC microlensing events seen
by the MACHO Project is unknown. The most popular explanations include a
previously unknown population of old, cool white dwarfs in the Galactic halo
or in a very thick disk, or a variation standard LMC models that would allow
most events to be caused by faint LMC stars. This uncertainty exists because
it is usually impossible to determine the lens distance from the observable
features of a microlensing event. Distance estimates can be obtained by
measuring the microlensing parallax effect with simultaneous observations of
the events from Earth and from a small (~30cm) telescope located 1-2 AU from
the Earth. Such a telescope has just been launched: the High Resolution
Instrument on the flyby spacecraft of the Deep Impact (DI) Mission. This
telescope has been placed in an ideal orbit for LMC microlensing parallax
measurements, and the telescope will be at a distance of >1 AU from Earth when
the DI prime mission ends this August. Our group plans to take advantage of
this fortuitous circumstance and propose a "new science" extended mission for
the DI flyby spacecraft to resolve the LMC microlensing puzzle with
microlensing parallax observaions. This project is compatible with the DI
Science Teams extended mission plans to visit a 2nd comet, and our extended
mission proposal to NASA will be written in collaboration with the Deep Impact
Science team. A crucial feature of these proposed microlensing parallax
measurements is the determination of the absolute brightness of the source
stars, which can only be resolved with HST images. The source star brightness
must be measured over the entire sensitivity range of the Deep Impact High
Resolution Instrument clear filter: 300-1000nm. We therefore request UBVriz
HST images to resolve the blending of the microlensed LMC source stars
observed by the Deep Impact 30cm telescope.
================================================================================
Proposal Category: GO
Scientific Category: SOLAR SYSTEM
ID: 10545
Title: Icy planetoids of the outer solar system
PI: Michael Brown
PI Institution: California Institute of Technology
Early HST studies of satellites of Kuiper belt object focussed on the 50-200
km objects that were the largest known at the time. In the past 3 years we
have discovered a population of much more rare and much larger (500-2000+ km)
icy planetoids in the Kuiper belt. These objects are the largest and brightest
known in the Kuiper belt and, in the era when we now know of more than 1000
Kuiper belt objects, these few planetoids are likely to be the focus of much
of the research on physical properties of the outer solar system for years to
come. We are currently engaged in an intensive program involving Spitzer,
Keck, and other telescopes to study the physical and dynamical properties of
this new population. HST is uniquely capable of addressing one parameter
fundamental to completing the physical picture of these planetoids: the
existence and size of any satellites. The detection and characterization of
satellites to these large planetoids would allow us to address unique issues
critical to the formation and evolution of the outer solar system, including
the measurement of densities, internal properties, sizes and shapes of these
objects, the study of binary formation as a function of primary size, and the
context of the Pluto-Charon binary. For these bright objects, a satellite
search takes less than a full orbit, allowing the opportunity for a new
project on UV spectroscopy of the planetoids to piggyback at no added time
cost. This poorly explored spectral range has the potential to show unique
signatures of trapped gasses, cosmochemically important ices, and complex
organic materials.
================================================================================
Proposal Category: GO
Scientific Category: COSMOLOGY
ID: 10546
Title: The filaments of NGC1275
PI: Andrew Fabian
PI Institution: University of Cambridge
The spectacular H-0alpha filaments stretching over 100 kpc around the central
galaxy in the nearby Perseus cluster of galaxies, NGC1275, resemble those
found around distant radio galaxies and some protogalaxies. The origin and
ionization of the filaments are poorly understood and relate to heating and
cooling processes in galaxy formation and evolution. We propose here to image
the filaments in order to reveal their true small-scale structure and to
search for clumps of young stars along them. The observations will produce the
first deep high resolution images of the whole filament system and, with our 1
Ms Chandra image, constrain both particle and photon ionization models for its
ionization and excitation.
================================================================================
Proposal Category: SNAP
Scientific Category: ISM AND CIRCUMSTELLAR MATTER
ID: 10547
Title: A SNAP Program to Obtain Complete Wavelength Coverage of
Interstellar Extinction
PI: Edward Fitzpatrick
PI Institution: Villanova University
We propose a SNAP program to obtain ACS/HRC spectra in the near-UV (PR200L)
and near-IR (G800L) for a set of main sequence B stars with available IUE UV
spectrophotometry, optical photometry, and 2MASS IR photometry. Together with
these existing data, the new observations will provide complete photometric
and spectrophotometric coverage from 1150 to 11000 A and enable us to produce
complete extinction curves from the far-UV to the near-IR, with well-
determined values of R(V). The proposed set of 50 program sight lines includes
the full range of interstellar extinction curve types and a wide range of
color excesses. The new data will allow us to examine variability in the near-
UV through near-IR spectral regions, including the UV-optical "knee" and the
"Very Broad Structure." We will examine the response of these features to
different interstellar environments and their relationship to other curve
features. These are largely unexplored aspects of extinction curves which will
provide additional constraints on the properties of interstellar grains. The
curves will be derived using stellar atmosphere models to represent the
intrinsic spectral energy distributions of the program stars, eliminating the
need to observe unreddened "standard stars." This approach virtually
eliminates "mismatch error", allowing us to derive extinction curves with much
higher precision than previously possible. In addition, the new spectra will
provide higher S/N data for the peak of the 2175 A bump than previously
available.
================================================================================
Proposal Category: SNAP
Scientific Category: AGN/QUASARS
ID: 10548
Title: Near-UV Snapshot Survey of Low Luminosity AGNs
PI: Rosa Gonzalez Delgado
PI Institution: Instituto de Astrofisica de Andalucia (IAA)
Low-luminosity active galactic nuclei (LLAGNs) comprise ~30% of all bright
galaxies (B<12.5) and are the most common type of AGN. These include low-
luminosity Seyfert galaxies, LINERs, and transition-type objects (TOs, also
called weak-[OI] LINERs). What powers them is still at the forefront of AGN
research. To unveil the nature of the central source we propose a near-UV
snapshot survey of 50 nearby LLAGNs using ACS/HRC and the filter (F330W), a
configuration which is optimal to detect faint star forming regions around
their nuclei. These images will complement optical and near-IR images
available in the HST archive, providing a panchromatic atlas of the inner
regions of these galaxies, which will be used to study their nuclear stellar
population. Our main goals are to: 1) Investigate the presence of nuclear
unresolved sources that can be attributed to an AGN; 2) Determine the
frequency of nuclear and circumnuclear stellar clusters, and whether they are
more common in Transition Objects (TOs) than in LINERs; 3) Characterize the
sizes, colors, luminosities, masses and ages of these clusters; 4) Derive
the luminosity function of star clusters and study their evaporation over time
in the vicinity of AGNs. Finally, the results of this project will be combined
with those of a previous similar one for Seyfert galaxies in order to compare
the nature of the nuclear sources and investigate if there could be an
evolution from Seyferts to TOs and LINERs. By adding UV images to the existing
optical and near-IR ones, this project will also create an extremely valuable
database for astronomers with a broad range of scientific interests.
================================================================================
Proposal Category: GO
Scientific Category: ISM AND CIRCUMSTELLAR MATTER
ID: 10549
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 384 years,
as it morphs into the youngest supernova remnant at age 18. HST is the unique
and perfect tool for spatially-resolved observations of the many physical
components of SN 1987A. A violent encounter is underway between the fastest-
moving debris and the circumstellar ring, exciting hotspots seen with HST that
are suddenly lighting up. The optical and X-ray flux from the ring are both
rising rapidly: HST and Chandra observations taken together are needed to
understand the physics of these shocked regions. In Cycle14, the hotspots may
fuse as the shock fully enters the ring. Photons from these shocks may excite
previously hidden gas outside the ring, revealing the true extent of the mass
loss that preceded the explosion. The inner debris of the explosion itself,
still excited by radioactive isotopes produced in the explosion, is now well
resolved by ACS and seen to be aspherical, providing direct clues to the
mechanism of the explosion. Our search for a compact remnant is beginning to
eliminate some theoretical possibilities and we have the opportunity in Cycle
14 to place much more stringent limits with NICMOS. Many questions about SN
1987A remain unanswered. How did the enigmatic three rings form in the late
stages of Sanduleak -69 202? Precisely what took place in the center during
the core collapse and bounce? Is a black hole or a neutron star left behind in
the debris? SAINTS has been a continuous program since HST was launched-- we
propose to extend this rich and deep data set for present use and future
reference to answer these central questions in the science of supernovae.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10550
Title: The Nature of LSB galaxies revealed by their Globular
Clusters
PI: Markus Kissler-Patig
PI Institution: European Southern Observatory - Germany
Low Surface Brightness (LSB) galaxies encompass many of the extremes in galaxy
properties. Their understanding is essential to complete our picture of galaxy
formation and evolution. Due to their historical under-representation on
galaxy surveys, their importance to many areas of astronomy has only recently
began to be realized. Globular clusters are superb tracers of the formation
histories of galaxies and have been extensively used as such in high surface
brightness galaxies. We propose to investigate the nature of massive LSB
galaxies by studying their globular cluster systems. No globular cluster study
has been reported for LSB galaxies to date. Yet, both the presence or absence
of globular clusters set very strong constraints on the conditions prevailing
during LSB galaxy formation and evolution. Both in dwarf and giant high
surface brightness (HSB) galaxies, globular clusters are known to form as a
constant fraction of baryonic mass. Their presence/absence immediately
indicates similarities or discrepancies in the formation and evolution
conditions of LSB and HSB galaxies. In particular, the presence/absence of
metal-poor halo globular clusters infers similarities/differences in the halo
formation and assembly processes of LSB vs. HSB galaxies, while the
presence/absence of metal-rich globular clusters can be used to derive the
occurrence and frequency of violent events (such as mergers) in the LSB galaxy
assembly history. Two band imaging with ACS will allow us to identify the
globular clusters (just resolved at the selected distance) and to determine
their metallicity (potentially their rough age). The composition of the
systems will be compared to the extensive census built up on HSB galaxies. Our
representative sample of six LSB galaxies (cz < 2700 km/s) are selected such,
that a large system of globular clusters is expected. Globular clusters will
constrain phases of LSB galaxy formation and evolution that can currently not
be probed by other means. HST/ACS imaging is the only facility capable of
studying the globular cluster systems of LSB galaxies given their distance and
relative scarcity.
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Proposal Category: GO
Scientific Category: GALAXIES
ID: 10551
Title: Gamma-Ray Bursts from Start to Finish: A Legacy Approach
PI: Shrinivas Kulkarni
PI Institution: California Institute of Technology
The progenitors of long-duration GRBs are now known to be massive stars. This
result lends credence to the collapsar model, where a rotating massive star
ends its life leaving a black hole or a highly magnetized neutron star, and
confirms its essential aspects. The focus of attention now is on the black
hole or magnetar engines that power the bursts. Somehow these engines create
the most highly relativistic and highly collimated outflows that we know of,
through mechanisms that no current theory can explain. These astrophysical
laboratories challenge our understanding of relativistic shocks, of mechanisms
for extracting energy from a black hole, and of how physics works in extreme
conditions. The launch of Swift is bringing us into a new era, where we can
make broadband observations that will enable us to study these fascinating
physical processes. We propose here an ambitious, comprehensive program to
obtain the datasets that will become the standard that any successful model
for the central engine must explain. This programs leverages the HST
observations to the maximum extent by our commitment of Swift observations, a
Large program at the VLA, and extensive ground-based optical resources. By
studying the engines and searching for jets in a variety of events, this
program will investigate the conditions necessary for the engine and jet
formation itself.
================================================================================
Proposal Category: GO
Scientific Category: STAR FORMATION
ID: 10552
Title: The distance of the Orion Nebula Cluster
PI: Massimo Robberto
PI Institution: Space Telescope Science Institute - ESA
The HST Treasury program on the Orion Nebula, currently in execution, has
surprisingly found that background sources are easily detected by HST at long
wavelengths through selected fields within the nebula. We propose to use these
background sources as a reference system to measure the trigonometric parallax
of the Orion Nebula cluster. Using ACS in the F850LP filter and with a modest
investment of HST time, we will reduce the error on the ~500pc distance of the
Orion Nebula to ~15pc, or less, improving by a factor ~6 over current
estimates. Our new value will have a major impact on star formation studies,
allowing to determine with high accuracy the absolute luminosity of the
cluster members and all derived stellar parameters (agee, masses, mass
accretion rates...). Our current understanding of a great range of phenomena
associated to the star formation activity in Orion will also benefit from an
improved distance estimate.
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Proposal Category: GO
Scientific Category: AGN/QUASARS
ID: 10553
Title: Bipolar Scattering Structures in AGN
PI: Gary Schmidt
PI Institution: University of Arizona
The Unified Scheme for Seyfert galaxies successfully explains the basic
distinctions between Type 1 and Type 2 AGN, including the existence of broad
scattered lines in polarized flux spectra of the latter. However, it fails to
account for the strongly polarized broad lines often observed in Type 1 AGN.
We have discovered an intermediate type red QSO that exhibits polarization
properties of both types; indeed it suggests a bipolar scattering geometry
similar to that seen in Galactic protoplanetary nebulae. We request a small
allocation with the high-resolution camera on ACS to image the object in two
key spectral bands. The results will allow an unambiguous interpretation of
ground-based data, and enable modeling of the inclination and opening angle
that illuminates the scattering clouds. Like NGC 1068, a successful
explanation of this object will not only allow further unification of AGN but
also aid in unraveling the details of their inner structure.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10554
Title: Globular Cluster Systems of Elliptical Galaxies in Low
Density Environments
PI: Ray Sharples
PI Institution: University of Durham
We propose to use the ACS/WFC to determine colour (metallicity) distributions
and luminosity functions for the globular cluster populations in a well-
defined sample of elliptical galaxies in low-density environments, and to
compare the results with similar samples taken from a rich cluster
environment. Low-luminosity ellipticals are now recognized to play a pivotal
role in testing hierarchical models of galaxy formation, and their globular
cluster populations provide a unique probe of their star formation and metal
enrichment history. The data will be used to (i) determine whether the bimodal
colour distributions indicative of multiple formation epochs in luminous
ellipticals are also prevalent in low-luminosity field ellipticals; (ii) place
joint constraints on age and metallicity in systems with more than one
population and determine the spread of ages in any one system; (iii) test
whether cluster destruction processes (e.g. tidal shocking) are more effective
in low-luminosity ellipticals, as predicted from their higher mass densities.
ACS observations are essential to eliminate foreground/background
contamination and to probe deep into the luminosity function to obtain a good
statistical sample of clusters. The TAC has previously awarded HST time to two
large surveys of globular cluster systems in rich cluster environments, but
there is currently no comparable survey in low-density environments with which
to compare these results.
================================================================================
Proposal Category: GO
Scientific Category: SOLAR SYSTEM
ID: 10555
Title: A Search for Satellites Around Kuiper Belt Objects Which
Exhibit High Angular Momentum
PI: Scott Sheppard
PI Institution: Carnegie Institution of Washington
We propose to use the HST to search for satellites around Kuiper Belt Objects
which have large amplitude, fast rotational light curves. Large main belt
asteroids with similar light curve characteristics have been found to have
near an 80 percent companion rate. This is over an order of magnitude more
than the companion rate of main belt asteroids in general. The satellites
were probably formed during the process which imparted the high angular
momentum on the primary object. To date five Kuiper Belt objects exhibit high
angular momentum through their rotational light curves. Two of them have been
observed with STIS on the HST and one was found to be a binary. We request
three orbits with HST/ACS in order to obtain deep high resolution images of
the other three Kuiper Belt objects that have large amplitudes and fast
rotations. In addition, we request one orbit to reobserve the other KBO which
didn't have a satellite detection in order to obtain deeper and better
resolution images than the first observations. Finding binaries is important
not only to understand the processes which created the high angular momentum
of the primary but also in determining the bulk densities and collisional
histories of the objects.
================================================================================
Proposal Category: GO
Scientific Category: QUASAR ABSORPTION LINES AND IGM
ID: 10556
Title: Neutral Gas at Redshift z=0.5
PI: David Turnshek
PI Institution: University of Pittsburgh
Damped Lyman-alpha systems (DLAs) are used to track the bulk of the neutral
hydrogen gas in the Universe. Prior to HST UV spectroscopy, they could only be
studied from the ground at redshifts z>1.65. However, HST has now permitted us
to discover 41 DLAs at z<1.65 in our past surveys. Followup studies of these
systems are providing a wealth of information about the evolution of the
neutral gas phase component of the Universe. But one problem is that these 51
low-redshift systems are spread over a wide range of redshifts spanning nearly
70% of the age of the Universe. Consequently, past surveys for low-redshift
DLAs have not been able to offer very good precision in any small redshift
regime. Here we propose an ACS-HRC-PR200L spectroscopic survey in the redshift
interval z=[0.37,0.7] which we estimate will permit us to discover another 41
DLAs. This will not only allow us to double the number of low-redshift DLA,
but it will provide a relatively high-precision regime in the low-redshift
Universe that can be used to anchor evolutionary studies. Fortunately DLAs
have high absorption equivalent width, so ACS-HRC-PR200L has high-enough
resoultion to perform this proposed MgII-selected DLA survey.
================================================================================
Proposal Category: GO
Scientific Category: SOLAR SYSTEM
ID: 10557
Title: Probing Asteroid Families for Evidence of Ultraviolet
Space Weathering Effects
PI: Faith Vilas
PI Institution: NASA Johnson Space Center
We propose six HST orbits to obtain UV reflectance spectra covering 200-460 nm
of two Vesta asteroid family members, asteroid 832 Karin, and two Karin family
members. These observations extend work done under a Cycle 13 AR grant, where
we analyzed all of the existing IUE and HST S-class asteroids in the MAST
database to investigate the effects of space weathering at UV wavelengths.
Our hypothesis is that the manifestation of space weathering at UV wavelengths
is a spectral bluing, in contrast with a spectral reddening at visible-NIR
wavelengths, and that UV wavelengths can be more sensitive to relatively small
amounts of weathering than longer wavelengths. The proposed observations will
address two objectives: (1) Measure the UV-visible spectra of 832 Karin and
two members of the young Karin family (absolute age of 5.8 My), in order to
determine whether intermediate space weathering is observable in objects
likely pristine when they originated from the interior of Karin's parent body.
(2) Measure the UV-visible spectra of two members of the Vesta family to
compare with our analysis of IUE Vesta spectra. These observations will probe
Vesta's interior, and test our hypothesis by contrasting the apparent amount
of alteration on the surfaces of Vestoids with excavated material on Vesta.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10558
Title: Archaeology of Fossil Galaxy Groups
PI: Michael West
PI Institution: University of Hawaii
Fossil groups are concentrations of dark mater with masses and x-ray
luminosities comparable to those of an entire group of galaxies, but whose
light is dominated by a single, isolated, large elliptical galaxy. The
origin of these systems remains a puzzle: they may be the end products of
complete merging of galaxies within once normal groups, or they might
originate from a very unusual galaxy luminosity function in those regions that
inhibits the formation of moderate-sized galaxies. We propose the first study
of the globular cluster populations of the dominant elliptical galaxies in
fossil galaxy groups, which will provide important new insights into their
origin.
================================================================================
Proposal Category: GO
Scientific Category: COOL STARS
ID: 10559
Title: Astrometric monitoring of binary L and T dwarfs
PI: Herve Bouy
PI Institution: Instituto de Astrofisica de Canarias
We propose to obtain high angular resolution ACS images of five binary L and T
dwarfs in order to determine their orbital parameters and dynamical masses,
and directly constrain the evolutionary models of ultracool and substellar
objects. The binaries have estimated periods ranging between 5 and 14 years.
All of them have already been resolved at least twice (sometimes more) using
HST, providing first and second epochs measurements. We propose to obtain two
more ACS imaging observations separated by 9 to 12 months during cycle 14. The
expected period coverage should therefore range between 35% and 117%, allowing
us to compute precise orbital parameters and masses. Our sample is large
enough and covers a sufficiently wide range of spectral types (from L3 to
T5.5) to allow us to obtain strong constraints the evolutionnary models.
================================================================================
Proposal Category: GO
Scientific Category: ISM AND CIRCUMSTELLAR MATTER
ID: 10560
Title: Confirming Planetary Candidates in the Stellar Graveyard
with NICMOS
PI: John Debes
PI Institution: The Pennsylvania State University
We propose to follow up planetary candidates imaged near the white dwarf WD
1620-391 with second epoch images from NICMOS. This white dwarf was imaged
during Cycle 12 as part of a campaign to detect massive planetary companions
to nearby white dwarfs with photospheric metal line absorption. While at a
low galactic latitude, a puzzling excess of objects are present < 4",
suggesting the possiblity of objects physically associated with the white
dwarf. With second epoch information we can test these candidates for common
proper motion, a test for physical association. If any of these candidates
are confirmed, they will be consistent with 6-10 M$_{Jup}$ companions at
projected orbital separations of between 25-50 AU.
================================================================================
Proposal Category: GO
Scientific Category: HOT STARS
ID: 10561
Title: A deep UV imaging survey of the Globular Cluster M 30
PI: Andrea Dieball
PI Institution: University of Southampton
We propose to carry out a deep FUV and NUV survey of M30 (NGC 7099) in order
to find and study the hot and/or dynamically-formed stellar populations in the
globular cluster. In particular, we will (i) search for the UV counterpart to
a MSP binary, (ii) find and study the full population of cataclysmic variables
in this cluster, (iii) study the UV properties of the cluster's extensive blue
straggler population, (iv) detect the first set of white dwarfs in this
cluster. Our survey will be sensitive to variability on time-scales from
minutes to weeks, allowing us to search for variable stars in all of the FUV
populations.
================================================================================
Proposal Category: GO
Scientific Category: GALAXIES
ID: 10562
Title: Validating a dark galaxy
PI: Mike Disney
PI Institution: University of Wales, College of Cardiff (UWCC)
VIRGOHI21 is an object detected in the Virgo Cluster HI survey of Davies et
al (2004), with a velocity width typical of a disc galaxy (220 km/s) but which
does not appear to have an optical counterpart down to a surface brightness
level of 2