Phase I Proposals

Cycle 16 Abstract catalog (based on Phase I submissions)

Generated on: Mon Apr 9 12:08:20 EDT 2007

======================================================================

Proposal Category: GO

Scientific Category: COSMOLOGY

ID: 11099

Title: A "silver bullet" for the sources of reionization

PI: Marusa Bradac

PI Institution: Stanford University

Recent discoveries of z>6 galaxies have given us the first glimpse of the

Universe shortly after the era of reionization. The questions arose whether

these first galaxies can be made responsible for the reionization process, and

how long did it last. Neither observations nor theory provide a clean answer.

In particular observations give results that are barely mutually consistent

and need to be further tested. Observing high redshift (z>7) sources is in

general difficult, mostly due to the high luminosity distance to these

objects, and partly due to the lower expected stellar masses compared to

objects at moderate redshifts. We propose to use one of the most massive,

merging cluster 1E0657-56 (z=0.295) as a cosmic telescopes to efficiently

probe the high-redshift universe. The gravitational potential well of this

cluster provides several magnitudes of magnification, enabling study of

intrinsically lower luminosity galaxies.As we discuss in the proposal, due to

its highly elongated mass distribution and ideal redshift the bullet cluster

is a prime candidate for this study. We propose deep NICMOS and WFPC2

observations; with much reduced observing time compared to e.g. NICMOS UDF we

expect an order of magnitude more (~5 candidates) z>7 objects. They will also

likely be multiply imaged, and since the geometry of images depends upon the

redshift, we will be able to confirm their nature, thereby not requiring

(often prohibitive at these magnitudes) spectroscopic follow-up. This will

enable us to count high-redshift sources and constrain their luminosity

function; a task made possible with the help of gravitational lensing even in

the pre-JWST era.

======================================================================

Proposal Category: GO

Scientific Category: COSMOLOGY

ID: 11100

Title: Two new `bullets' for MOND: revealing the properties of dark matter in massive merging clusters

PI: Marusa Bradac

PI Institution: Stanford University

The principal objective of this proposal is to study the physical nature of

dark matter by using two, massive, newly-identified merging clusters of

galaxies. As shown by the pioneering example of the ``bullet cluster''

(1E0657-56), such systems are ideal laboratories for detecting dark matter and

distinguishing between cold dark matter (CDM) and other scenarios (e.g. self-

interacting dark matter). Our limit on the self-interaction cross-section of

dark matter relies on the assumption of a normal pre-merger mass-to-light

ratios, and a small impact parameter during the collision of the two clusters.

In order to mitigate any possible systematic effects, it is vital to extend

this work to other, similar systems. With detailed observations of new

systems, the systematic uncertainties in the dark matter cross section

calculations can be improved substantially, allowing us to move from rough

order of magnitude estimates to measurements with quantifiable uncertainties

that can be compared usefully with the predictions from numerical simulations.

Our targets are two extraordinary, high-redshift, merging galaxy clusters

recently discovered by the Massive Cluster Survey (MACS). This survey is by

far the best matched to this study, since it selects medium redshift (optimal

for gravitational lensing studies) and X-ray luminous (hence massive) objects.

We have selected the best candidates with clear evidence for considerable

offsets between the hot X-ray emitting gas and optically luminous stellar

material. The two most striking examples are the targets of this proposal. To

pin down the position of the dark matter component we require high resolution,

absolutely calibrated mass maps. The combination of weak and strong lensing

measurements is needed to attain this goal. This can only be achieved with the

excellent resolving power of the HST (in combination with wide-field,

multicolor Subaru data already in hand). We therefore request multicolor

HST/WFPC2 observations of the two merging clusters. The combination of

constraints from multiply lensed images (identified via morphology and color

information) and high-resolution weak lensing data will allow us to construct,

self-consistently, their mass distribution from the very centers to the

outskirts. Gravitational lensing thus provides a unique tool transforming

these clusters into dark matter laboratories. They will supply us with answers

as to the nature and properties of dark matter, and how it shapes galaxies and

galaxy clusters and their evolution through cosmic time.

======================================================================

Proposal Category: GO

Scientific Category: AGN/QUASARS

ID: 11101

Title: The Relevance of Mergers for Fueling AGNs: Answers from QSO Host Galaxies

PI: Gabriela Canalizo

PI Institution: University of California - Riverside

The majority of QSOs are known to reside in centers of galaxies that look like

ellipticals. Numerical simulations have shown that remnants of galaxy mergers

often closely resemble elliptical galaxies. However, it is still strongly

debated whether the majority of QSO host galaxies are indeed the result of

relatively recent mergers or whether they are completely analogous to inactive

ellipticals to which nothing interesting has happened recently. To address

this question, we recently obtained deep HST ACS images for five QSO host

galaxies that were classified morphologically as ellipticals (GO-10421). This

pilot study revealed striking signs of tidal interactions such as ripples,

tidal tails, and warped disks that were not detected in previous studies. Our

observations show that at least some "elliptical" QSO host galaxies are the

products of relatively recent merger events rather than old galaxies formed at

high redshift. However, the question remains whether the host galaxies of

classical QSOs are truly distinct from inactive ellipticals and whether there

is a connection between the merger events we detect and the current nuclear

activity. We must therefore place our results into a larger statistical

context. We are currently conducting an HST archival study of inactive

elliptical galaxies (AR-10941) to form a control sample. We now propose to

obtain deep HST/WFPC2 images of 13 QSOs whose host galaxies are classified as

normal ellipticals. Comparing the results for both samples will help us

determine whether classical QSOs reside in normal elliptical galaxies or not.

Our recent pilot study of five QSOs indicates that we can expect exciting

results and deep insights into the host galaxy morphology also for this larger

sample of QSOs. A statistically meaningful sample will help us determine the

true fraction of QSO hosts that suffered strong tidal interactions and thus,

whether a merger is indeed a requirement to trigger nuclear activity in the

most luminous AGNs.

======================================================================

Proposal Category: GO

Scientific Category: SOLAR SYSTEM

ID: 11102

Title: HST as a Jovian Climate Satellite

PI: Imke de Pater

PI Institution: University of California - Berkeley

In the past year, there have been striking changes in Jupiter's atmosphere.

Among these are the Oval BA's change from white to red, two new dark

Disturbances in the southern hemisphere, and a 30% change (since 1997) in the

aspect ratio of the potential vorticity anomaly of the GRS (not just its

associated clouds), as we determined from high-accuracy velocities extracted

from HST images. The determination of high-accuracy velocities requires both

high-resolution imaging by HST (or flybys), and our novel adaptation of

Correlation Image Velocimetry (CIV), a technique that has far greater accuracy

than the traditional method (of identifying velocity tie-points by hand). Our

proposed observations will test the hypothesis that these changes in Jupiter

validate our 2004 prediction: that the merger of the 3 White Ovals in 1998-

2000 would lead to climate change on Jupiter. The key is to determine, by

indirect means, the temperature at the base of the weather layer, a quantity

that cannot be observed directly at any wavelength. The new Red Oval BA's

velocities will be used to test our finding that the color change is due to

global temperature changes. The change in the GRS's aspect ratio suggests a

large (at least 20%) change in the shear of the local velocity since 1997. The

latter can be investigated only by determining Jupiter's current zonal winds.

======================================================================

Proposal Category: SNAP

Scientific Category: COSMOLOGY

ID: 11103

Title: A Snapshot Survey of The Most Massive Clusters of Galaxies

PI: Harald Ebeling

PI Institution: University of Hawaii

We propose the continuation of our highly successful SNAPshot survey of a

sample of 125 very X-ray luminous clusters in the redshift range 0.3-0.7. As

demonstrated by the 25 snapshots obtained so far in Cycle14 and Cycle15 these

systems frequently exhibit strong gravitational lensing as well as spectacular

examples of violent galaxy interactions. The proposed observations will

provide important constraints on the cluster mass distributions, the physical

nature of galaxy-galaxy and galaxy-gas interactions in cluster cores, and a

set of optically bright, lensed galaxies for further 8-10m spectroscopy. All

of our primary science goals require only the detection and characterisation

of high-surface-brightness features and are thus achievable even at the

reduced sensitivity of WFPC2. Because of their high redshift and thus compact

angular scale our target clusters are less adversely affected by the smaller

field of view of WFPC2 than more nearby systems. Acknowledging the broad

community interest in this sample we waive our data rights for these

observations. Due to a clerical error at STScI our approved Cycle15 SNAP

program was barred from execution for 3 months and only 6 observations have

been performed to date - reinstating this SNAP at Cycle16 priority is of

paramount importance to reach meaningful statistics.

======================================================================

Proposal Category: GO

Scientific Category: AGN/QUASARS

ID: 11104

Title: The nature of radio transients

PI: Avishay Gal-Yam

PI Institution: California Institute of Technology

We have conducted the first ever blind, wide-field survey for radio transients

(Levinson et al. 2002; Gal-Yam et al. 2006). We have discovered four radio

transients and explored their nature using radio and optical follow-up

observations. One is a known pulsar, one is a z~0.1 AGN, and one is most

probably an optically obscured radio supernova (SN) in the nearby galaxy NGC

4216 (the first such event to be discovered by a wide field radio survey). The

last source appears not to be associated with a bright host galaxy (to a limit

of R < 24.5 mag). We request 4 orbits of WFPC2 F606W imaging to check whether

we can establish an association between this radio transient and any of three

nearby faint resolved galaxies we have detected from the ground. If the source

is associated with any of these galaxies it would represent a new type of

extra-galactic radio bursts, more luminous than, e.g., radio afterglows of

gamma-ray bursts. Alternatively, ruling out an association with these galaxies

would disfavor an extra-galactic nature of this object, and suggest instead

that this is a radio outburst of a faint Galactic compact object, probably a

new type of radio-flaring neutron star. If this is the case, the high

luminosity (9 mJy) and relatively high galactic latitude (33 degrees) of this

source may indicate it is relatively nearby. This single source represents a

large population (comparable in sky density to AGN, pulsars, and radio SNe)

and thus merits intensive study. A modest investment of HST time, leveraged by

massive ground-based radio and optical efforts, will allow us to identify a

new class of radio sources, and complete a census of the variable radio sky

down to ~6 mJy, leaving no unidentifed objects. This result can be directly

scaled to predict the number and type of transient sources expected to be

detected by future surveys with the next generation radio arrays, such as ATA

and SKA.Since our science critically requires HST's spatial resolution (rather

than sensitivity) it is perfectly suited to be carried out with WFPC2.

======================================================================

Proposal Category: GO

Scientific Category: RESOLVED STELLAR POPULATIONS

ID: 11105

Title: The LBV progenitor of SN 2005gl - a new key to massive star evolution puzzles

PI: Avishay Gal-Yam

PI Institution: California Institute of Technology

The currently accepted theory regarding the last stages of massive star

evolution maintains that the evolution of the envelope is coupled to that of

the stellar core. For this reason, very massive stars are expected to shed

their outer hydrogen envelopes before they develop large iron cores, and

ultimately, explode as core-collapse supernovae (SNe). It is therefore a

strict prediction of current models that massive stars (certainly those above

~40 solar mass) will explode as hydrogen-poor SNe, i.e., of Types Ib and Ic.

In particular, the class of luminous blue variables (LBVs) such as eta-Carina,

which are known to be very massive (up to 100 solar masses and above) are

expected to lose their entire hydrogen envelopes prior to their ultimate

explosions as SNe. However, using pre-explosion HST/WFPC2 imaging of the

location of the recent hydrogen-rich type IIn SN 2005gl, we have identified

(Gal-Yam et al. 2007) its putative progenitor as a very luminous point source

(with absolute V magnitude of -10.2). If this is a single star, it must be an

LBV from luminosity considerations (no other stars are as luminous). If our

progenitor identification is correct, at least in some cases, massive stars

explode before losing most of their hydrogen envelope, indicating the core and

envelope are decoupled, and requiring revision of stellar evolution theory.

Here, we propose a single-orbit HST observation of the location of SN 2005gl

designed to test whether the point source we identified as its LBV progenitor

has indeed disappeared (as expected from a single star) or remained unchanged

(as expected, e.g., if it is a compact star cluster). These data are the last

observational ingredient required to firmly establish (or refute) the

explosion of an LBV as a type IIn SN, with fundamental implications for the

theory of massive star evolution. Since the new data will be compared to pre-

explosion WFPC2 images, this program is perfectly suited to be carried out

with the WFPC2 camera.

======================================================================

Proposal Category: GO

Scientific Category: SOLAR SYSTEM

ID: 11106

Title: Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus

PI: Heidi Hammel

PI Institution: Space Science Institute

The planet Uranus is demonstrating increased atmospheric activity as it

approaches its 2007 equinox, perhaps in response to extreme insolation change.

Convective sites in the planet's southern hemisphere reached unprecedented

altitudes in 2003 (Hammel et al. 2005, Icarus 175, 284); a bright northern

feature showed the highest contrast yet detected in an outer planet atmosphere

(Sromovsky et al. 2007, Icarus, submitted); and a dark atmospheric feature was

detected by HST for the first time (Hammel et al. 2007, in preparation). The

historical record makes references to discrete structures (both bright and

dark) on Uranus during previous equinoctial apparitions (the last equinox

occurred in 1965). The best amateur facilities are now just able to resolve

the disk of Uranus and detect such activity if it is very large or has very

high contrast. Amateurs also have access to a great many nights of telescope

time. If a discrete cloud feature on Uranus is reported through the amateur

network, we propose to obtain follow-up images with HST's WFPC2. The proposed

TOO images will permit determination of detailed structure of the feature at

visible wavelengths, and will provide vertical and horizontal constraints on

the feature's scattering properties. HST is the only facility that can

provide such information at visible wavelengths.

======================================================================

Proposal Category: GO

Scientific Category: COSMOLOGY

ID: 11107

Title: Imaging of Local Lyman Break Galaxy Analogs: New Clues to Galaxy Formation in the Early Universe

PI: Timothy Heckman

PI Institution: The Johns Hopkins University

We have used the ultraviolet all-sky imaging survey currently being conducted

by the Galaxy Evolution Explorer (GALEX) to identify for the first time a rare

population of low-redshift starbursts with properties remarkably similar to

high-redshift Lyman Break Galaxies (LBGs). These "compact UV luminous

galaxies" (UVLGs) resemble LBGs in terms of size, SFR, surface brightness,

mass, metallicity, kinematics, dust, and color. The UVLG sample offers the

unique opportunity of investigating some very important properties of LBGs

that have remained virtually inaccessible at high redshift: their morphology

and the mechanism that drives their star formation. Therefore, in Cycle 15 we

have imaged 7 UVLGs using ACS in order to 1) characterize their morphology and

look for signs of interactions and mergers, and 2) probe their star formation

histories over a variety of timescales. The images show a striking trend of

small-scale mergers turning large amounts of gas into vigorous starbursts (a

process referred to as dissipational or "wet" merging). Here, we propose to

complete our sample of 31 LBG analogs using the ACS/SBC F150LP (FUV) and WFPC2

F606W (R) filters in order to create a statistical sample to study the

mechanism that triggers star formation in UVLGs and its implications for the

nature of LBGs. Specifically, we will 1) study the trend between galaxy

merging and SFR in UVLGs, 2) artificially redshift the FUV images to z=1-4 and

compare morphologies with those in similarly sized samples of LBGs at the same

rest-frame wavelenghts in e.g. GOODS, UDF, and COSMOS, 3) determine the

presence and morphology of significant stellar mass in "pre-burst" stars, and

4) study their immediate environment. Together with our Spitzer (IRAC+MIPS),

GALEX, SDSS and radio data, the HST observations will form a unique union of

data that may for the first time shed light on how the earliest major episodes

of star formation in high redshift galaxies came about. This proposal was

adapted from an ACS HRC+WFC proposal to meet the new Cycle 16 observing

constraints, and can be carried out using the ACS/SBC and WFPC2 without

compromising our original science goals.

======================================================================

Proposal Category: GO

Scientific Category: COSMOLOGY

ID: 11108

Title: Near Infrared Observations of a Sample of z~6.5-6.7 Galaxies

PI: Esther Hu

PI Institution: University of Hawaii

The majority of the most distant galaxies discovered to date have been found

by strong Lyman alpha emission at red optical wavelengths. An accurate

estimate of the star formation rates for these objects requires a measurement

of the line-free UV continuum, which must be taken at infrared wavelengths.

Here we propose to obtain imaging with NICMOS in the F160W filter for a sample

of 9 Lyman alpha galaxies with redshifts z~6.5 up to z=6.740 from a complete,

flux-limited widefield narrowband and multi-color survey conducted on the 8-m

Subaru Telescope. This program will investigate galaxy morphologies and star

formation for a uniform sample of the highest redshift galaxies now known.

======================================================================

Proposal Category: GO

Scientific Category: SOLAR SYSTEM

ID: 11109

Title: Characterization of the UV absorption feature in asteroid (1) Ceres

PI: Jianyang Li

PI Institution: University of Maryland

We propose to obtain the UV spectrum of asteroid (1) Ceres from 120 nm to 200

nm with ACS/SBC objective prism to characterize the broad and deep absorption

feature within this wavelength range as reported recently. Our scientific

goals include, 1) to characterize the absorption band, 2) to determine the

origin of this spectral feature and constrain the surface compositions of

Ceres, and 3) to understand the albedo and color features on Ceres. HST is

the only observatory currently capable of obtaining spectroscopy in this

wavelength range. This observation will help improve our knowledge about this

largest and oldest asteroid, and support the planning of the upcoming NASA

Discovery Program mission, Dawn, orbiting asteroids Vesta and Ceres.

======================================================================

Proposal Category: GO

Scientific Category: ISM IN EXTERNAL GALAXIES

ID: 11110

Title: Searching for Lyman alpha Emission from FUSE Lyman Continuum Candidates

PI: Stephan McCandliss

PI Institution: The Johns Hopkins University

We have recently been granted time on FUSE to characterize the escape fraction

of hydrogen Lyman continuum (Lyc) photons from a morphologically diverse set

of star forming galaxies. The FUSE program is designed to provide ~ 5 sigma

detections of Lyc photons emitted from star forming galaxies with escape

fractions ~5%. With this proposal we seek hydrogen Lyman alpha (Lya)

observations of a representative subset of the FUSE program targets to

constrain the observational relationship between Lyc, Lya, and hydrogen Balmer

line emission in these systems. Such observations explore the detailed

balance between the simple optically thin (Case A) and optically thick (Case

B) limits in recombination theory. The ultimate goal of this program is to

quantify the relationship between escaping Lya and Lyc emission and the first

structures that form in the early universe.

======================================================================

Proposal Category: GO

Scientific Category: RESOLVED STELLAR POPULATIONS

ID: 11111

Title: A Search for an Intermediate Mass Black Hole in the Globular Cluster NGC 6266

PI: Bernard McNamara

PI Institution: New Mexico State University

We propose to search for an intermediate mass black hole (IMBH) in the core of

the galactic globular cluster NGC 6266. Based on a comparison between the

observed central surface brightness profiles of 38 globular clusters and

state-of-the art N-body simultations, NGC 6266 offers the best hope of

detecting an IMBH among these objects. This detection would be significnat for

at least two reasons. It would be the first concrete discovery of an IMBH,

revealing unique information about the environment in which these objects

form, and second, its discovery would provide a powerful validation on the N-

body simultations used to track the dynamical evolution of globular clusters.

======================================================================

Proposal Category: GO

Scientific Category: UNRESOLVED STELLAR POPULATIONS

ID: 11112

Title: The Collisional Ring Galaxy NGC922

PI: Gerhardt Meurer

PI Institution: The Johns Hopkins University

We request WFPC2 images of the newly recognized collisional ring galaxy NGC922

which will become the nearest such system observed by HST. These will be used

to get a clear understanding of the geometry of the interaction and the

induced star formation in this system. Quantitive modeling of the colors of

the star clusters and stellar populations will be used to constrain the star

formation history of the system. They will also be used to test the "infant

mortality" scenario for star cluster evolution. The derived population ages

will test predictions of how star formation evolves in the various components

(ring, core, spokes) of collisional rings, and will improve our own

simulations of this system. These will be used to determine the final fate of

the stars formed in the present burst - some will end up in a central bar or

bulge while others will become part of a thickened disk. By analogy this will

tell us how similar collisions enrich stellar populations in the early

universe. This is especially relevant since the number density of collisional

rings increases rapidly with redshift.

======================================================================

Proposal Category: SNAP

Scientific Category: SOLAR SYSTEM

ID: 11113

Title: Binaries in the Kuiper Belt: Probes of Solar System Formation and Evolution

PI: Keith Noll

PI Institution: Space Telescope Science Institute

The discovery of binaries in the Kuiper Belt and related small body

populations is powering a revolutionary step forward in the study of this

remote region. Three quarters of the known binaries in the Kuiper Belt have

been discovered with HST, most by our snapshot surveys. The statistics

derived from this work are beginning to yield surprising and unexpected

results. We have found a strong concentration of binaries among low-

inclination Classicals, a possible size cutoff to binaries among the Centaurs,

an apparent preference for nearly equal mass binaries, and a strong increase

in the number of binaries at small separations. We propose to continue this

successful program in Cycle 16; we expect to discover at least 13 new binary

systems, targeted to subgroups where these discoveries can have the greatest

impact.

======================================================================

Proposal Category: GO

Scientific Category: ISM AND CIRCUMSTELLAR MATTER

ID: 11114

Title: Improving proper motion measurements of the stars in the field of SN 1572 with WFPC2

PI: Pilar Ruiz-Lapuente

PI Institution: Universidad de Barcelona

We propose to complete the spatial velocity measurements of the stars in the

central region of the remnant of SN 1572, one of the historical Galactic Type

Ia supernovae. A new visit with WFPC2 would allow us to significantly improve

the accuracy of the proper motion measurements of the stars in the field,

since we would benefit from a long temporal baseline by using the WFPC2 images

previously taken. This unique legacy would complement the high-precision

ground-based observations made for the stars in the SN 1572 field during the

past ten years. The search for the companion star of Galactic Type Ia

supernovae, based on their high peculiar velocity as a salient feature, has

already pointed to a good candidate for SN 1572. The current uncertainties in

the tangential velocity of the candidate star and the other stars in the field

can be reduced to less than a half with a visit in Cycle 16. This would lead

to a precise determination of the parameters of the binary system that gave

rise to the supernova. If not done during Cycle 16, the long temporal baseline

for SN 1572 with WFPC2 would be lost.

======================================================================

Proposal Category: GO

Scientific Category: SOLAR SYSTEM

ID: 11115

Title: Photometric Imaging of Asteroid 2 Pallas

PI: Christopher Russell

PI Institution: University of California - Los Angeles

We propose to conduct the first HST imaging of Asteroid 2 Pallas with WFPC2-PC

over 8 HST orbits. We will image the asteroid in five filters: F336w, F439w,

F555w, F675w and F814w. We will utilize these observations to drastically

improve the knowledge of Pallas' shape, spin pole position and surface

properties, including roughness and albedo, parameters that are poorly

determined by previous study. These observations will result in high signal-

to-noise, high resolution surface maps from the visible to the UV. A

satellite search will also be conducted for objects within the stability field

of up to 21st magnitude, or about 900m in diameter. It is demonstrated in our

proposal that significant scientific opportunity exists in Cycle 16 because

Pallas is at both a low-phase, 3.9 degree opposition and near its closest

approach to Earth, conditions that do not occur simultaneously in the next

twenty years. This window represents the best chance to answer long standing,

fundamental questions about Pallas, the main asteroid belt, and the formation

of the solar system.

======================================================================

Proposal Category: GO

Scientific Category: COOL STARS

ID: 11116

Title: Exploring the Early FUV History of Cool Stars: Transition Regions at 30 Myr

PI: Steven Saar

PI Institution: Smithsonian Institution Astrophysical Observatory

Stellar magnetic activity derives from the so-called "dynamo," a hydromagnetic

interplay between overturning plasma motions and differential rotation in

stars cool enough to support significant surface convection zones. The

magnetic fields resulting from dynamo action are in turn are responsible for a

wide range of high-energy emissions, including the spectacular outbursts

called flares. Dynamo powered magnetic activity is not confined solely to

stars, but also must occur, for example, in accretion disks of all

descriptions, and in some planets. A great deal is known about magnetic

activity in middle-aged G dwarfs like our Sun, thanks to its proximity. Less

is known, however, about the much younger stars, newly emerged from the T-

Tauri stage. Yet, it is during this phase that they reach the peak of their

magnetic activity, and subsidiary influences, such as the impact of ionizing

radiation and strong coronal winds on developing solar systems, also are

maximum. One of the key missing ingredients in our current understanding are

measurements of FUV emissions of such stars, to complement the extensive

collections of coronal (1-10 MK) X-ray measurements, particularly from recent

ROSAT, Chandra and XMM-Newton surveys. We propose to conduct sensitive

ACS/SBC prism ultraviolet spectroscopy of selected fields in two young (30

Myr) Galactic clusters--IC 2391 and IC 2602--to inventory the key C IV

emission index (~0.1 MK) over a much larger and more diverse sample of coeval

objects than has been possible hitherto. A key question is whether the FUV

emissions also suffer the "saturation" and "super-saturation" at short

rotation periods seen in coronal X-rays, or whether they continue to rise in

the fastest rotating stars. The saturation behavior of the different

temperature regimes holds important clues to the organization of the surface

active regions on these very young stars, and should allow us to distinguish

among several competing models.

======================================================================

Proposal Category: GO

Scientific Category: STAR FORMATION

ID: 11117

Title: The Search for Atmospheric Water in the Transiting Planet HD189733b

PI: David Sing

PI Institution: CNRS, Institut d'Astrophysique de Paris

We propose to use the NICMOS camera to search for transit NIR signatures of

atmospheric water in HD189733b. While water absorption bands exist in the

optical and IR, space-based NIR signatures are uniquely positioned to offer

the best chance at detection. Using narrow band photometric filters, we will

be able to detect absorption signatures while the planet is in primary

transit. A positive detection would be the first proof of water on an

extrasolar planet. Furthermore, it would provide invaluable planetary

information, constraining the entire chemistry. As a byproduct of the high

SNR required for our primary science goal, we will be able to improve on the

value of the planetary radius, a result independent of our primary science

objective. The accurate radius estimate, together with planet structure

models, will allow constraining the planet interior and its relationship with

formation models and stellar metallicity.

======================================================================

Proposal Category: GO

Scientific Category: SOLAR SYSTEM

ID: 11118

Title: Investigating Near-Equinox Atmospheric Change on Uranus

PI: Lawrence Sromovsky

PI Institution: University of Wisconsin - Madison

Uranus is approaching its 7 December 2007 equinox, when we will be able to

observe the entire northern hemisphere for the first time with modern cameras.

The large seasonal phase shift expected from its long radiative time constant

implies that it should now exhibit nearly maximal hemispheric contrast, and

should be in the process of reversing. Many changes already observed, such as

the development of the first visible-wavelength dark spot, discovered in Cycle

15, and the fading of the south polar cap may be indicative of the expected

reversal. We propose a detailed characterization of Uranus' current seasonal

response with a 7-orbit program consisting of 1 orbit of NICMOS imaging of

cloud bands and 6 orbits of WFPC2 imaging using both broadband and narrow-band

filters capable of tracking dark and bright discrete cloud features. Filters

between 0.467 and 1.87 microns will provide vertical sensing depths scanning

through the pressure range where the putative methane and deeper H2S clouds

might plausibly exist and provide strong constraints on their contributions

and parent gas mixing ratios. These observations have unique combinations of

spectral range and resolution with needed temporal and spatial resolution not

available from groundbased observations. Only HST is capable of investigating

the Uranus dark spot.

======================================================================

Proposal Category: GO

Scientific Category: HOT STARS

ID: 11119

Title: The Stellar Origins of Supernovae

PI: Schuyler Van Dyk

PI Institution: Jet Propulsion Laboratory

Supernovae (SNe) have a profound effect on galaxies, and have been used

recently as precise cosmological probes, resulting in the discovery of the

accelerating Universe. They are clearly very important events deserving of

intense study. Yet, even with nearly 4000 known SNe, we know relatively

little about the stars which give rise to these powerful explosions. The main

limitation has been the lack of spatial resolution in pre-SN imaging data.