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Daily Report #5111

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Old June 7th 10, 12:42 PM posted to sci.astro.hubble
Cooper, Joe
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Posts: 568
Default Daily Report #5111

HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science


PERIOD COVERED: 5am June 4 - 5am June 7, 2010 (DOY 155/09:00z-158/09:00z)


Significant Spacecraft Anomalies: (The following are preliminary
reports of potential non-nominal performance that will be


12294 - GSAcq(2,1,1) scheduled at 156/15:48:00z and REAcq(2,1,1)
scheduled at 156/17:25:05z and at 156/19:00:56z was observed to have
resulted in fine lock backup (2,0,2) using FGS-2.

Observations possibly affected: COS 198 - 213, Proposal ID#11536

12295 - GSAcq(2,1,1) scheduled at 157/03:37:28z failed to fine lock
backup on FGS 2.

Observations possibly affected: WFC3 147 - 149, Proposal ID#11662.



FGS GSAcq 26 26
FGS REAcq 21 21
OBAD with Maneuver 24 24



WFC3/UVIS 12018

Ultra-Luminous X-Ray Sources in the Most Metal-Poor Galaxies

There is growing observational and theoretical evidence to suggest
that Ultra-Luminous X-ray sources (ULX) form preferentially in low
metallicity environments. Here we propose a survey of 27 nearby (
30Mpc) star-forming Extremely Metal Poor Galaxies (Z5% solar). There
are almost no X-ray observations of such low abundance galaxies (3 in
the Chandra archive). These are the most metal-deficient galaxies
known, and a logical place to find ULX if they favor metal-poor
systems. We plan to test recent population synthesis models which
predict that ULX should be very numerous in metal-poor galaxies. We
will also test the hypothesis that ULX form in massive young star
clusters, and ask for HST time to obtain the necessary imaging data.

ACS/WFC 12016

The Stars and Edge-on Disks of PDS 144: An Intermediate-Mass Analog of
Wide T Tauri Multiple Stars

High-Inclination PMS stars are optimally oriented to measure disk
size, height, to detect jets, and to directly probe disk composition.
Placing these data into evolutionary context requires dates for the
systems and measurements of L bol, and extinction. For such stars,
X-ray data provide L x, but also N(H) and the total extinction. FUV
data measures L UV, and constrains the shape of the extinction curve.
Recent studies have suggested that the frequency of Jovian-mass
planets is higher for systems with intermediate-mass stars, due to
disk mass or composition. While suitable low mass YSOs are
well-represented in the Chandra and HST archives, similar data are
lacking for higher mass systems. We propose joint Chandra and HST
imaging of PDS 144 to fill this gap.

ACS/WFC 11995

CCD Daily Monitor (Part 2)

This program comprises basic tests for measuring the read noise and
dark current of the ACS WFC and for tracking the growth of hot pixels.
The recorded frames are used to create bias and dark reference images
for science data reduction and calibration. This program will be
executed four days per week (Mon, Wed, Fri, Sun) for the duration of
Cycle 17. To facilitate scheduling, this program is split into three
proposals. This proposal covers 320 orbits (20 weeks) from 1 February
2010 to 20 June 2010.

WFC3/IR/S/C 11929

IR Dark Current Monitor

Analyses of ground test data showed that dark current signals are more
reliably removed from science data using darks taken with the same
exposure sequences as the science data, than with a single dark
current image scaled by desired exposure time. Therefore, dark current
images must be collected using all sample sequences that will be used
in science observations. These observations will be used to monitor
changes in the dark current of the WFC3-IR channel on a day-to-day
basis, and to build calibration dark current ramps for each of the
sample sequences to be used by Gos in Cycle 17. For each sample
sequence/array size combination, a median ramp will be created and
delivered to the calibration database system (CDBS).

WFC3/IR 11926

IR Zero Points

We will measure and monitor the zeropoints through the IR filters
using observations of the white dwarf standard stars, GD153, GD71 and
GD191B2B and the solar analog standard star, P330E. Data will be taken
monthly during Cycle 17. Observations of the star cluster, NGC 104,
are made twice to check color transformations. We expect an accuracy
of 2% in the wide filter zeropoints relative to the HST photometric
system, and 5% in the medium- and narrow-band filters.

WFC3/UVIS 11912

UVIS Internal Flats

This proposal will be used to assess the stability of the flat field
structure for the UVIS detector throughout the 15 months of Cycle 17.
The data will be used to generate on-orbit updates for the delta-flat
field reference files used in the WFC3 calibration pipeline, if
significant changes in the flat structure are seen.

WFC3/UVIS 11908

Cycle 17: UVIS Bowtie Monitor

Ground testing revealed an intermittent hysteresis type effect in the
UVIS detector (both CCDs) at the level of ~1%, lasting hours to days.
Initially found via an unexpected bowtie-shaped feature in flatfield
ratios, subsequent lab tests on similar e2v devices have since shown
that it is also present as simply an overall offset across the entire
CCD, i.e., a QE offset without any discernable pattern. These lab
tests have further revealed that overexposing the detector to count
levels several times full well fills the traps and effectively
neutralizes the bowtie. Each visit in this proposal acquires a set of
three 3x3 binned internal flatfields: the first unsaturated image will
be used to detect any bowtie, the second, highly exposed image will
neutralize the bowtie if it is present, and the final image will allow
for verification that the bowtie is gone.

WFC3/UVIS 11905

WFC3 UVIS CCD Daily Monitor

The behavior of the WFC3 UVIS CCD will be monitored daily with a set
of full-frame, four-amp bias and dark frames. A smaller set of 2Kx4K
subarray biases are acquired at less frequent intervals throughout the
cycle to support subarray science observations. The internals from
this proposal, along with those from the anneal procedure (Proposal
11909), will be used to generate the necessary superbias and superdark
reference files for the calibration pipeline (CDBS).

COS/FUV 11897

FUV Spectroscopic Sensitivity Monitoring

The purpose of this proposal is to monitor sensitivity in each FUV
grating mode to detect any changes due to contamination or other


HST Cycle 17 and Post-SM4 Optical Monitor

This program is the Cycle 17 implementation of the HST Optical
Monitoring Program.

The 36 orbits comprising this proposal will utilize ACS (Wide Field
Channel) and WFC3 (UVIS Channel) to observe stellar cluster members in
parallel with multiple exposures over an orbit. Phase retrieval
performed on the PSF in each image will be used to measure primarily
focus, with the ability to explore apparent coma, and astigmatism
changes in WFC3.

The goals of this program are to: 1) monitor the overall OTA focal
length for the purposes of maintaining focus within science tolerances
2) gain experience with the relative effectiveness of phase retrieval
on WFC3/UVIS PSFs 3) determine focus offset between the imagers and
identify any SI-specific focus behavior and dependencies

If need is determined, future visits will be modified to interleave
WFC3/IR channel and STIS/CCD focii measurements.

STIS/CC 11847

CCD Bias Monitor-Part 2

Monitor the bias in the 1x1, 1x2, 2x1, and 2x2 bin settings at gain=1,
and 1x1 at gain = 4, to build up high-S/N superbiases and track the
evolution of hot columns.

STIS/CC 11845

CCD Dark Monitor Part 2

Monitor the darks for the STIS CCD.

WFC3/UV 11841

The Formation of Brightest Cluster Galaxies

We propose Chandra and HST observations of a unique low redshift
cluster in which the Brightest Cluster Galaxy (BCG) is in the process
of forming. The Chandra observations will be used to study the impact
of BCG formation on the properties of the intracluster medium. We will
test whether galaxy merging can destroy cool cores and disrupt hot gas
halos. We will also explore the role of intracluster stars in
enriching the intracluster medium. The HST observations will be used
to search for extended tidal features and young star clusters and to
estimate the final stellar mass of the BCG. The low redshift of our
target allows a more detailed study of BCG formation than is possible
with higher redshift systems.

FGS 11789

An Astrometric Calibration of Population II Distance Indicators

In 2002, HST produced a highly precise parallax for RR Lyrae. That
measurement resulted in an absolute magnitude, M(V)= 0.61+/-0.11, a
useful result, judged by the over ten refereed citations each year
since. It is, however, unsatisfactory to have the direct,
parallax-based, distance scale of Population II variables based on a
single star. We propose, therefore, to obtain the parallaxes of four
additional RR Lyrae stars and two Population II Cepheids, or W Vir
stars. The Population II Cepheids lie with the RR Lyrae stars on a
common K-band Period-Luminosity relation. Using these parallaxes to
inform that relationship, we anticipate a zero point error of 0.04
magnitude. This result should greatly strengthen confidence in the
Population II distance scale and increase our understanding of RR
Lyrae star and Pop. II Cepheid astrophysics.

FGS 11788

The Architecture of Exoplanetary Systems

Are all planetary systems coplanar? Concordance cosmogony makes that
prediction. It is, however, a prediction of extrasolar planetary
system architecture as yet untested by direct observation for main
sequence stars other than the Sun. To provide such a test, we propose
to carry out FGS astrometric studies on four stars hosting seven
companions. Our understanding of the planet formation process will
grow as we match not only system architecture, but formed planet mass
and true distance from the primary with host star characteristics for
a wide variety of host stars and exoplanet masses.

We propose that a series of FGS astrometric observations with
demonstrated 1 millisecond of arc per-observation precision can
establish the degree of coplanarity and component true masses for four
extrasolar systems: HD 202206 (brown dwarf+planet); HD 128311
(planet+planet), HD 160691 = mu Arae (planet+planet), and HD 222404AB
= gamma Cephei (planet+star). In each case the companion is identified
as such by assuming that the minimum mass is the actual mass. For the
last target, a known stellar binary system, the companion orbit is
stable only if coplanar with the AB binary orbit.


Probing HeII Reionization with GALEX-selected Quasar Sightlines and

We propose spectroscopic observations with COS of eight z~3 QSOs that
we found to be bright in the far ultraviolet. Our aim is to study
intergalactic absorption caused by the onset of the He II Lyman
forest. Several lines of evidence suggest that helium reionization
occurred at z~3. Understanding this process is critical for a complete
picture of the intergalactic medium and its evolution; it also gives
clues to hydrogen reionization at z6. The only direct means of
assessing He II reionization is through far-UV observations of the He
II Lyman alpha forest. Only 6 sightlines are known to date where this
is feasible, despite extensive surveys. Our program is designed to
double the number of available sightlines. To this effect, we
cross-correlated all known z2.73 quasars with UV source lists from
the GALEX satellite. The selected quasars were all significantly
detected in the far UV by GALEX, and their UV colors are similar to
those of already known quasars with transparent sightlines. Spectra
obtained with COS will allow us to compile the first comprehensive
sample of He II absorption spectra probing similar redshifts, enabling
a systematic investigation of the He II reionization epoch and the
spectral shape of the UV background.


The Impact of Starbursts on the Gaseous Halos of Galaxies

Perhaps the most important (yet uncertain) aspects of galaxy evolution
are the processes by which galaxies accrete gas and by which the
resulting star formation and black hole growth affects this accreting
gas. It is believed that both the form of the accretion and the nature
of the feedback change as a function of the galaxy mass. At low mass
the gas comes in cold and the feedback is provided by massive stars.
At high mass, the gas comes in hot, and the feedback is from an AGN.
The changeover occurs near the mass where the galaxy population
transitions from star-forming galaxies to red and dead ones. The
population of red and dead galaxies is building with cosmic time, and
it is believed that feedback plays an important role in this process:
shutting down star formation by heating and/or expelling the reservoir
of cold halo gas. To investigate these ideas, we propose to use COS
far-UV spectra of background QSOs to measure the properties of the
halo gas in a sample of galaxies near the transition mass that have
undergone starbursts within the past 100 Myr to 1 Gyr. The galactic
wind associated with the starburst is predicted to have affected the
properties of the gaseous halo. To test this, we will compare the
properties of the halos of the post-starburst galaxies to those of a
control sample of galaxies matched in mass and QSO impact parameter.
Do the halos of the post-starburst galaxies show a higher incidence
rate of Ly-Alpha and metal absorption-lines? Are the kinematics of the
halo gas more disturbed in the post-starbursts? Has the wind affected
the ionization state and/or the metallicity of the halo? These data
will provide fresh new insights into the role of feedback from massive
stars on the evolution of galaxies, and may also offer clues about the
properties of the QSO metal absorption-line systems at high-redshift .

FGS 11704

The Ages of Globular Clusters and the Population II Distance Scale

Globular clusters are the oldest objects in the universe whose age can
be accurately determined. The dominant error in globular cluster age
determinations is the uncertain Population II distance scale. We
propose to use FGS 1R to obtain parallaxes with an accuracy of 0.2
milliarcsecond for 9 main sequence stars with [Fe/H] -1.5. This will
determine the absolute magnitude of these stars with accuracies of
0.04 to 0.06mag. This data will be used to determine the distance to
24 metal-poor globular clusters using main sequence fitting. These
distances (with errors of 0.05 mag) will be used to determine the ages
of globular clusters using the luminosity of the subgiant branch as an
age indicator. This will yield absolute ages with an accuracy of 5%,
about a factor of two improvement over current estimates. Coupled with
existing parallaxes for more metal-rich stars, we will be able to
accurately determine the age for globular clusters over a wide range
of metallicities in order to study the early formation history of the
Milky Way and provide an independent estimate of the age of the

The Hipparcos database contains only 1 star with [Fe/H] -1.4 and an
absolute magnitude error less than 0.18 mag which is suitable for use
in main sequence fitting. Previous attempts at main sequence fitting
to metal-poor globular clusters have had to rely on theoretical
calibrations of the color of the main sequence. Our HST parallax
program will remove this source of possible systematic error and yield
distances to metal-poor globular clusters which are significantly more
accurate than possible with the current parallax data. The HST
parallax data will have errors which are 10 times smaller than the
current parallax data. Using the HST parallaxes, we will obtain main
sequence fitting distances to 11 globular clusters which contain over
500 RR Lyrae stars. This will allow us to calibrate the absolute
magnitude of RR Lyrae stars, a commonly used Population II distance

WFC3/IR 11696

Infrared Survey of Star Formation Across Cosmic Time

We propose to use the unique power of WFC3 slitless spectroscopy to
measure the evolution of cosmic star formation from the end of the
reionization epoch at z6 to the close of the galaxy- building era at
z~0.3.Pure parallel observations with the grisms have proven to be
efficient for identifying line emission from galaxies across a broad
range of redshifts. The G102 grism on WFC3 was designed to extend this
capability to search for Ly-alpha emission from the first galaxies.
Using up to 250 orbits of pure parallel WFC3 spectroscopy, we will
observe about 40 deep (4-5 orbit) fields with the combination of G102
and G141, and about 20 shallow (2-3 orbit) fields with G141 alone.

Our primary science goals at the highest redshifts a (1) Detect Lya
in ~100 galaxies with z5.6 and measure the evolution of the Lya
luminosity function, independent of of cosmic variance; 2) Determine
the connection between emission line selected and continuum-break
selected galaxies at these high redshifts, and 3) Search for the
proposed signature of neutral hydrogen absorption at re-ionization. At
intermediate redshifts we will (4) Detect more than 1000 galaxies in
Halpha at 0.5z1.8 to measure the evolution of the
extinction-corrected star formation density across the peak epoch of
star formation. This is over an order-of-magnitude improvement in the
current statistics, from the NICMOS Parallel grism survey. (5) Trace
``cosmic downsizing" from 0.5z2.2; and (6) Estimate the evolution in
reddening and metallicty in star- forming galaxies and measure the
evolution of the Seyfert population. For hundreds of spectra we will
be able to measure one or even two line pair ratios -- in particular,
the Balmer decrement and [OII]/[OIII] are sensitive to gas reddening
and metallicity. As a bonus, the G102 grism offers the possibility of
detecting Lya emission at z=7-8.8.

To identify single-line Lya emitters, we will exploit the wide
0.8--1.9um wavelength coverage of the combined G102+G141 spectra. All
[OII] and [OIII] interlopers detected in G102 will be reliably
separated from true LAEs by the detection of at least one strong line
in the G141 spectrum, without the need for any ancillary data. We
waive all proprietary rights to our data and will make high-level data
products available through the ST/ECF.

ACS/WFC3 11670

The Host Environments of Type Ia Supernovae in the SDSS Survey

The Sloan Digital Sky Survey Supernova Survey has discovered nearly
500 type Ia supernovae and created a large, unique, and uniform sample
of these cosmological tools. As part of a comprehensive study of the
supernova hosts, we propose to obtain Hubble ACS images of a large
fraction of these galaxies. Integrated colors and spectra will be
measured from the ground, but we require high-resolution HST imaging
to provide accurate morphologies and color information at the site of
the explosion. This information is essential in determining the
systematic effects of population age on type Ia supernova luminosities
and improving their reliability in measuring dark energy. Recent
studies suggest two populations of type Ia supernovae: a class that
explodes promptly after star-formation and one that is delayed by
billions of years. Measuring the star-formation rate at the site of
the supernova from colors in the HST images may be the best way to
differentiate between these classes.

WFC3/UVIS/IR 11662

Improving the Radius-Luminosity Relationship for Broad-Lined AGNs with
a New Reverberation Sample

The radius-luminosity (R-L) relationship is currently the fundamental
basis for all techniques used to estimate black hole masses in AGNs,
in both the nearby and distant universe. However, the current R-L
relationship is based on 34 objects that cover a limited range in
black hole mass and luminosity. To improve our understanding of black
hole growth and evolution, the R-L relationship must be extended to
cover a broader range of black hole masses using the technique known
as reverberation mapping. To this end, we have been awarded an
unprecedented 64 nights on the Lick Observatory 3-m telescope between
March 24 and May 31, 2008, to spectroscopically monitor 12 AGNs in
order to measure their black hole masses. To properly determine the
luminosities of these 12 AGNs, we must correct them for their
host-galaxy starlight contributions using high-resolution images.
Previous work by Bentz et al. (2006) has shown that the starlight
correction to AGN luminosity measurements is an essential component to
interpreting the R-L relationship. The correction will be substantial
for each of the 12 sources we will monitor, as the AGNs are relatively
faint and embedded in nearby, bright galaxies. Starlight corrections
are not possible with ground-based images, as the PSF and bulge
contributions become indistinguishable under typical seeing
conditions, and adaptive optics are not yet operational in the
spectral range where the corrections are needed. In addition, spectral
decompositions are very model-dependent and are limited by the degree
of accuracy to which we understand emission processes and stellar
populations in galaxies. Without correcting for starlight, we will be
unable to apply the results of our Spring 2008 campaign to the body of
knowledge from previous reverberation mapping work. Therefore, we
propose to obtain high resolution, high dynamic range images of the
host galaxies of the 12 AGNs in our ground-based monitoring sample, as
well as one white dwarf which will be used as a PSF model.

WFC3/IR 11648

WFC3 Spectroscopy of an X-ray Luminous Galaxy Cluster at z2

We propose to obtain deep WFC3+G141 grism observations to
spectroscopically confirm a remarkable z2 cluster of galaxy
candidate. Over a 1000 arcmin^2 field imaged with Spitzer’s IRAC we
have discovered a compact (30’’ diameter) concentration of extremely
red galaxies with a factor of 40 overdensity over the adjacent field.
Among these galaxies for which we can derive meaningful photometric
redshifts, 17 are consistent with zphot=2-2.5, making it very likely
that the concentration is a real cluster at such high redshift. This
is further supported by a 3.5 sigma detection of extended X-Ray
emission on XMM-Newton data, by a likely color?magnitude sequence of
red galaxies, and by the presence of a giant galaxy consistent with a
BCG at the cluster redshift. The general faintness of the red galaxies
in all optical bands and their high redshifts prevent confirmation of
this cluster with ordinary optical spectroscopy. The WFC3 camera with
G141 grism provides the only way to confirm this record high-z cluster
and measure its redshift from spectral breaks typical of old stellar
populations. Our deep integrations will reveal redshifts for at least
19 ultra-red galaxies in the area and of a similar number of bluer
galaxies at the cluster redshift. Knowledge of the cluster redshift
based on the HST spectra will allow us to reach important scientific
aims: find the most distant X?ray emitting evolved galaxy cluster,
determine membership of the other galaxies from photometric SED
analysis, study their stellar population properties, characterize the
color-magnitude relation with constraints on the formation redshift.
The proposed observations will establish a first z2 benchmark for
cluster?field comparisons of galaxy formation at this highest redshift
and will firmly establish the progenitors of local rich Abell

WFC3/UVIS/IR 11644

A Dynamical-Compositional Survey of the Kuiper Belt: A New Window Into
the Formation of the Outer Solar System

The eight planets overwhelmingly dominate the solar system by mass,
but their small numbers, coupled with their stochastic pasts, make it
impossible to construct a unique formation history from the dynamical
or compositional characteristics of them alone. In contrast, the huge
numbers of small bodies scattered throughout and even beyond the
planets, while insignificant by mass, provide an almost unlimited
number of probes of the statistical conditions, history, and
interactions in the solar system. To date, attempts to understand the
formation and evolution of the Kuiper Belt have largely been dynamical
simulations where a hypothesized starting condition is evolved under
the gravitational influence of the early giant planets and an attempt
is made to reproduce the current observed populations. With little
compositional information known for the real Kuiper Belt, the test
particles in the simulation are free to have any formation location
and history as long as they end at the correct point. Allowing
compositional information to guide and constrain the formation,
thermal, and collisional histories of these objects would add an
entire new dimension to our understanding of the evolution of the
outer solar system. While ground based compositional studies have hit
their flux limits already with only a few objects sampled, we propose
to exploit the new capabilities of WFC3 to perform the first ever
large-scale dynamical-compositional study of Kuiper Belt Objects
(KBOs) and their progeny to study the chemical, dynamical, and
collisional history of the region of the giant planets. The
sensitivity of the WFC3 observations will allow us to go up to two
magnitudes deeper than our ground based studies, allowing us the
capability of optimally selecting a target list for a large survey
rather than simply taking the few objects that can be measured, as we
have had to do to date. We have carefully constructed a sample of 120
objects which provides both overall breadth, for a general
understanding of these objects, plus a large enough number of objects
in the individual dynamical subclass to allow detailed comparison
between and within these groups. These objects will likely define the
core Kuiper Belt compositional sample for years to come. While we have
many specific results anticipated to come from this survey, as with
any project where the field is rich, our current knowledge level is
low, and a new instrument suddenly appears which can exploit vastly
larger segments of the population, the potential for discovery -- both
anticipated and not -- is extraordinary.

WFC3/UV 11605

Obtaining the Missing Links in the Test of Very Low Mass Evolutionary
Models with HST

We are proposing for spatially resolved ACS+HRC observations of 11
very low mass binaries spanning late-M, L and T spectral types in
order to obtain precise effective temperature measurements for each
component. All of our targets are part of a program in which we are
measuring dynamical masses of very low-mass binaries to an
unprecedented precision of 10% (or better). However, without precise
temperature measurements, the full scientific value of these mass
measurements cannot be realized. Together, mass and temperature
measurements will allow us to distinguish between brown dwarf
evolutionary models that make different assumptions about the interior
and atmospheric structure of these ultra-cool objects. While dynamical
masses can be obtained from the ground in the near-IR, obtaining
precise temperatures require access to optical data which, for these
sub-arcsecond binaries, can only be obtained from space with Hubble.

WFC3/UVIS 11595

Turning Out the Light: A WFC3 Program to Image z2 Damped Lyman Alpha

We propose to directly image the star-forming regions of z2 damped
Lya systems (DLAs) using the WFC3/UVIS camera on the Hubble Space
Telescope. In contrast to all previous attempts to detect the galaxies
giving rise to high redshift DLAs, we will use a novel technique that
completely removes the glare of the background quasar. Specifically,
we will target quasar sightlines with multiple DLAs and use the higher
redshift DLA as a ``blocking filter'' (via Lyman limit absorption) to
eliminate all FUV emission from the quasar. This will allow us to
carry out a deep search for FUV emission from the lower redshift DLA,
shortward of the Lyman limit of the higher redshift absorber. The
unique filter set and high spatial resolution afforded by WFC3/UVIS
will then enable us to directly image the lower redshift DLA and thus
estimate its size, star- formation rate and impact parameter from the
QSO sightline. We propose to observe a sample of 20 sightlines,
selected primarily from the SDSS database, requiring a total of 40 HST
orbits. The observations will allow us to determine the first FUV
luminosity function of high redshift DLA galaxies and to correlate the
DLA galaxy properties with the ISM characteristics inferred from
standard absorption-line analysis to significantly improve our
understanding of the general DLA population.

WFC3/UV/IR 11573

Investigating Post-Equinox Atmospheric Changes on Uranus

Uranus is now past its 7 December 2007 equinox. The large seasonal
phase shift expected from its long radiative time constant implies
that it should now be in the process of reversing its hemispheric
asymmetries in cloud band structure and zonal circulation. Many
changes already observed -- the development of the first
visible-wavelength dark spot, discovered in Cycle 15, the fading of
the south polar cap, and the development of a new northern bright band
while the southern band fades -- may all be indicative of the expected
reversal. We propose a detailed characterization of Uranus' current
seasonal response with a 9-orbit program consisting of 3 orbits of
WFC3 imaging of cloud bands and dark spots, and 6 orbits of high
signal-to-noise imaging using the F845M filter, capable of tracking
bright discrete cloud features. Filters between 0.467 and 1.7 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 sampling and
spatial resolution not available from groundbased observations.


Narrowing in on the Hubble Constant and Dark Energy

A measurement of the Hubble constant to a precision of a few percent
would be a powerful aid to the investigation of the nature of dark
energy and a potent "end-to end" test of the present cosmological
model. In Cycle 15 we constructed a new streamlined distance ladder
utilizing high- quality type Ia supernova data and observations of
Cepheids with HST in the near-IR to minimize the dominant sources of
systematic uncertainty in past measurements of the Hubble constant and
reduce its total uncertainty to a little under 5%. Here we propose to
exploit this new route to reduce the remaining uncertainty by more
than 30%, translating into an equal reduction in the uncertainty of
the equation of state of dark energy. We propose three sets of
observations to reach this goal: a mosaic of NGC 4258 with WFC3 in
F160W to triple its sample of long period Cepheids, WFC3/F160W
observations of the 6 ideal SN Ia hosts to triple their samples of
Cepheids, and observations of NGC 5584 the host of a new SN Ia, SN
2007af, to discover and measure its Cepheids and begin expanding the
small set of SN Ia luminosity calibrations. These observations would
provide the bulk of a coordinated program aimed at making the
measurement of the Hubble constant one of the leading constraints on
dark energy.


COS-GTO: Sleuthing the Source of Distant Cometary Activity

Distant comets and Centaurs often show cometary activity and outbursts
well beyond 3 AU, the boundary of the sublimation zone of water.
Super-volatiles (most likely CO, but possibly CH4, N2, or S2) are
suspected to be responsible, but have never been detected in distant
comets in the UV. We will obtain FUV spectra of active bodies to cover
important CO emission bands. We plan two sets of observations: comet
29P/Schwassmann-Wachmann at 6 AU, whose outbursts are too short to
capture as a Target of Opportunity, but which also shows persistent
cometary activity in quiescence; and Target of Opportunity
observations of the Centaur 2060 Chiron (at ~15.5 AU) in outburst.

ACS/WFC 11338

Continued M31 Monitoring for Black Hole X-ray Nova

During A01-7 we found 16 Black Hole X-ray Novae (BHXN) in M31 using
Chandra, and with HST followup have estimated orbital periods for 6 of
these. Observations are underway with HST to attempt to estimate
additional periods. We propose to continue this program, concentrating
our scarce HST resources on a single transient which exceeds the NS
Eddington limit. Only uninterrupted monitoring can yield the duty
cycles and long-term lightcurves of BHXN (and other variables) in M31.
Our GO+GTO programs have accumulated 300ks (ACIS) near the M31 bulge,
and total ACIS exposure on M31 is now 620ks. Our monitoring program
alone can amass 500ks on the bulge if continued through AO12, and
combined with other programs will reach 1Msec ACIS exposure on the

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