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Daily Report #5102



 
 
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Old May 24th 10, 02:24 PM posted to sci.astro.hubble
Cooper, Joe
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Posts: 568
Default Daily Report #5102

HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science

DAILY REPORT #5102

PERIOD COVERED: 5am May 21 - 5am May 24, 2010 (DOY 141/09:00z-144/09:00z)

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

12286 - GSAcq(1,2,1) at 141/18:30:00z fails to fine lock backup on FGS
2.

Observation possibly affected: proposal ID# 11704.

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)

SCHEDULED SUCCESSFUL
FGS GSAcq 24 24
FGS REAcq 23 23
OBAD with Maneuver 17 17

SIGNIFICANT EVENTS: (None)




OBSERVATIONS SCHEDULED

WFC3/IR/S/C 12089

Persistence - Part 2

The IR detectors on WFC3, like other IR detectors, trap charge when
exposed to sources near or above the full well of the detector diodes.
This charge leaks out, producing detectable afterglow images for
periods which can last for several hours, depending on the amount of
over exposure. These visits, which consist of tungsten lamp exposures
of varying durations followed by darks, are intended to provide a
better calibration of persistence over the full area of the IR
detector of WFC3.

COS/NUV/FUV 12086

Generation of 1-D Fixed Pattern Templates

Tests have shown that application of a 1-D fixed pattern template to a
COS spectrum can reduce the fixed pattern noise in G130M or G160M
spectra to an equivalent S/N of about 30/1. For this to be occur, the
template must be derived from data for the same grating and nearly the
same central wavelength as the observation. This is because each
grating has a different cross dispersion profile, and different
central wavelengths fall at different cross dispersion detector
locations. As a result, spectra obtained at each grating and central
wavelength setting are derived from different regions of the detectors
-- each with their own, unique detector features and grid wire
shadows.

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 11915

IR Internal Flat Fields

This program is the same as 11433 (SMOV) and depends on the completion
of the IR initial alignment (Program 11425). This version contains
three instances of 37 internal orbits: to be scheduled early, middle,
and near the end of Cycle 17, in order to use the entire 110-orbit
allocation.

In this test, we will study the stability and structure of the IR
channel flat field images through all filter elements in the WFC3-IR
channel. Flats will be monitored, i.e. to capture any temporal trends
in the flat fields and delta flats produced. High signal observations
will provide a map of the pixel-to-pixel flat field structure, as well
as identify the positions of any dust particles.

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 11907

UVIS Cycle 17 Contamination Monitor

The UV throughput of WFC3 during Cycle 17 is monitored via weekly
standard star observations in a subset of key filters covering
200-600nm and F606W, F814W as controls on the red end. The data will
provide a measure of throughput levels as a function of time and
wavelength, allowing for detection of the presence of possible
contaminants.

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/NUV 11900

NUV Internal/External Wavelength Scale Monitor

This program monitors the offsets between the wavelength scale set by
the internal wavecal versus that defined by absorption lines in
external targets. This is accomplished by observing two external
radial velocity standard targets: HD187691 with G225M and G285M and
HD6655 with G285M and G230L. The two standard targets have little flux
in the wavelength range covered by G185M and so Feige 48 (sdO) is
observed with this grating. Both Feige 48 and HD6655 are also observed
in SMOV. The cenwaves observed in this program are a subset of the
ones used during Cycle 17. Observing all cenwaves would require a
considerably larger number of orbits. Constraints on scheduling of
each target are placed so that each target is observed once every ~2-3
months. Observing the three targets every month would also require a
considerably larger number of orbits.

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.

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.

COS/NUV/FUV 11742

Probing HeII Reionization with GALEX-selected Quasar Sightlines and
HST/COS

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.

WFC3/UVIS 11732

The Temperature Profiles of Quasar Accretion Disks

We can now routinely measure the size of quasar accretion disks using
gravitational microlensing of lensed quasars. At optical wavelengths
we observe a size and scaling with black hole mass roughly consistent
with thin disk theory but the sizes are larger than expected from the
observed optical fluxes. One solution would be to use a flatter
temperature profile, which we can study by measuring the wavelength
dependence of the disk size over the largest possible wavelength
baseline. Thus, to understand the size discrepancy and to probe closer
to the inner edge of the disk we need to extend our measurements to UV
wavelengths, and this can only be done with HST. For example, in the
UV we should see significant changes in the optical/UV size ratio with
black hole mass. We propose monitoring 5 lenses spanning a broad range
of black hole masses with well-sampled ground based light curves,
optical disk size measurements and known GALEX UV fluxes during Cycles
17 and 18 to expand from our current sample of two lenses. We would
obtain 5 observations of each target in each Cycle, similar to our
successful strategy for the first two targets.

COS/NUV/FUV 11720

Detailed Analysis of Carbon Atmosphere White Dwarfs

We propose to obtain UV spectra for the newly discovered white dwarf
stars with a carbon- dominated atmosphere. Model calculations show
that these stars emit most of their light in the UV part of the
electromagnetic spectrum and that an accurate determination of the
flux in this region is crucial for an accurate determination of the
atmospheric parameters. It will also provide a unique opportunity to
test the atomic data and broadening theory in stellar conditions never
met before. This will play a primordial role in our path to understand
the origin of these objects as well to obtain a better understanding
of the evolution of stars in general. The principal objective we hope
to achieve with these observations are 1) obtain accurate surface
gravity/mass for these stars, 2) constrain/determine the abundance of
other elements (O, He, Mg, Ne etc.), especially oxygen, 3) verify the
accuracy of the various theoretical atomic data used in the model
calculations, 4) understand the origin and evolution of carbon
atmosphere white dwarfs, in particular whether progenitor stars as
massive as 10.5 solar masses can produce white dwarfs, rather than
supernovae. We propose to observe 5 objects chosen carefully to cover
the range of observed properties among carbon atmosphere white dwarfs
(effective temperature, surface gravity, abundance of hydrogen/helium
and magnetic field).

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
universe.

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
indicator.

WFC3/UVIS/IR 11702

Search for Very High-z Galaxies with WFC3 Pure Parallel

WFC3 will provide an unprecedented probe to the early universe beyond
the current redshift frontier. Here we propose a pure parallel program
using this new instrument to search for Lyman-break galaxies at
6.5z8.8 and to probe the epoch of reionization, a hallmark event in
the history of the early universe. We request 200 orbits, spreading
over 30 ~ 50 high Galactic latitude visits (|b|20deg) that last for 4
orbits and longer, resulting a total survey area of about 140~230
square arcminute. Based on our understanding of the new HST parallel
observation scheduling process, we believe that the total number of
long-duration pure parallel visits in Cycle 17 should be sufficient to
accommodate our program. We waive all proprietary rights to our data,
and will also make the enhanced data products public in a timely
manner.

(1) We will use both the UVIS and the IR channels, and do not need to
seek optical data from elsewhere.

(2) Our program will likely triple the size of the probable candidate
samples at z~7 and z~8, and will complement other targeted programs
aiming at the similar redshift range.

(3) Being a pure parallel program, our survey will only make very
limited demand on the scarce HST resources. More importantly, as the
pure parallel pointings will be at random sight-lines, our program
will be least affected by the bias due to the large scale structure
("cosmic variance").

(4) We aim at the most luminous LBG population, and will address the
bright-end of the luminosity function at z~8 and z~7. We will
constrain the value of L* in particular, which is critical for
understanding the star formation process and the stellar mass assembly
history in the first few hundred million years of the universe.

(5) The candidates from our survey, most of which will be the
brightest ones that any surveys would be able to find, will have the
best chance to be spectroscopically confirmed at the current 8--10m
telescopes.

(6) We will also find a large number of extremely red, old galaxies at
intermediate redshifts, and the fine spatial resolution offered by the
WFC3 will enable us constrain their formation history based on the
study of their morphology, and hence shed light on their connection to
the very early galaxies in the universe.

COS/FUV 11699

On the Evolutionary Status of Extremely Hot Helium Stars - are the
O(He) Stars Successors of the R CrB Stars?

We propose UV spectroscopy of the four unique post-AGB stars of
spectral type O(He) in order to understand the origin of their
peculiar surface abundances. These stars are the only known amongst
the hottest post-AGB stars (effective temperatures 100, 000 K) whose
atmospheres are composed of almost pure helium. This chemistry
markedly differs from that of the hydrogen-deficient post-AGB
evolutionary sequence with objects which have carbon dominated
atmospheres (PG1159 stars and Wolf-Rayet central stars).

While PG1159 and Wolf-Rayet stars are the result of a late
helium-shell flash, this scenario cannot explain the O(He) stars.
Instead, they are possibly double-degenerate mergers. We speculate
that the four O(He) stars represent evolved RCrB stars, which also
have helium-dominated atmospheres. We aim to determine the C, N, O,
and Si abundances precisely, in order to proof this evolutionary link.

COS/NUV/FUV 11698

The Structure and Dynamics of Virgo's Multi-Phase Intracluster Medium

The dynamical flows of the intracluster medium (ICM) are largely
unknown. We propose to map the spatial and kinematic distribution of
the warm ICM of the nearby Virgo cluster using the Cosmic Origins
Spectrograph. 15 sightlines at a range of impact parameters within the
virial radius of the cluster (0.2 - 1.7 Mpc) will be probed for
Lyman-alpha absorption and the data compared to blind HI, dust and
x-ray surveys to create a multi-phase map of the cluster's ICM.
Absorption line sightlines are commonly 40-100 kpc from a galaxy,
allowing the flow of baryons between galaxies and the ICM to be
assessed. The velocity distribution of the absorbers will be directly
compared to simulations and used to constrain the turbulent motions of
the ICM. This proposal will result in the first map of a cluster's
warm ICM and provide important tests for our theoretical understanding
of cluster formation and the treatment of gas cooling in cosmological
simulations.

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.

WFC3/UV/IR 11620

A Quasar Light Echo in the Local Universe?

The time history and duty cycle of individual AGN is an important part
of their evolution and the growth history of massive black holes, but
almost unconstrained on scales between galaxy-interaction timescales
(hundreds of Myr) and the scales of years probed by variability
measurements. We propose a detailed study of an object which seems to
be a large-scale light echo from a QSO-level episode in a nearby
galaxy. The Galaxy Zoo morphological survey of SDSS objects has
uncovered a peculiar emission-line structure whose spectrum matches
the narrow-line region of AGN, despite lying at least 20 kpc from a
galaxy whose activity is currently very weak. This is best explained
if the nucleus has faded dramatically on time scales of several tens
of thousands of years. We propose a suite of imaging and spectroscopic
observations to probe its properties, and the time history of this
episode of nuclear activity, measuring time scales hitherto
unavailable.

COS/NUV/FUV 11598

How Galaxies Acquire their Gas: A Map of Multiphase Accretion and
Feedback in Gaseous Galaxy Halos

We propose to address two of the biggest open questions in galaxy
formation - how galaxies acquire their gas and how they return it to
the IGM - with a concentrated COS survey of diffuse multiphase gas in
the halos of SDSS galaxies at z = 0.15 - 0.35. Our chief science goal
is to establish a basic set of observational facts about the physical
state, metallicity, and kinematics of halo gas, including the sky
covering fraction of hot and cold material, the metallicity of infall
and outflow, and correlations with galaxy stellar mass, type, and
color - all as a function of impact parameter from 10 - 150 kpc.
Theory suggests that the bimodality of galaxy colors, the shape of the
luminosity function, and the mass-metallicity relation are all
influenced at a fundamental level by accretion and feedback, yet these
gas processes are poorly understood and cannot be predicted robustly
from first principles. We lack even a basic observational assessment
of the multiphase gaseous content of galaxy halos on 100 kpc scales,
and we do not know how these processes vary with galaxy properties.
This ignorance is presently one of the key impediments to
understanding galaxy formation in general. We propose to use the
high-resolution gratings G130M and G160M on the Cosmic Origins
Spectrograph to obtain sensitive column density measurements of a
comprehensive suite of multiphase ions in the spectra of 43 z 1 QSOs
lying behind 43 galaxies selected from the Sloan Digital Sky Survey.
In aggregate, these sightlines will constitute a statistically sound
map of the physical state and metallicity of gaseous halos, and
subsets of the data with cuts on galaxy mass, color, and SFR will seek
out predicted variations of gas properties with galaxy properties. Our
interpretation of these data will be aided by state-of-the-art
hydrodynamic simulations of accretion and feedback, in turn providing
information to refine and test such models. We will also use Keck,
MMT, and Magellan (as needed) to obtain optical spectra of the QSOs to
measure cold gas with Mg II, and optical spectra of the galaxies to
measure SFRs and to look for outflows. In addition to our other
science goals, these observations will help place the Milky Way's
population of multiphase, accreting High Velocity Clouds (HVCs) into a
global context by identifying analogous structures around other
galaxies. Our program is designed to make optimal use of the unique
capabilities of COS to address our science goals and also generate a
rich dataset of other absorption-line systems

WFC3/ACS/IR 11597

Spectroscopy of IR-Selected Galaxy Clusters at 1 z 1.5

We propose to obtain WFC3 G141 and G102 slitless spectroscopy of
galaxy clusters at 1 z 1.5 that were selected from the IRAC survey
of the Bootes NDWFS field. Our IRAC survey contains the largest sample
of spectroscopically confirmed clusters at z 1. The WFC3 grism data
will measure H-alpha to determine SFR, and fit models to the low
resolution continua to determine stellar population histories for the
brighter cluster members, and redshifts for the red galaxies too faint
for ground-based optical spectroscopy.

WFC3/UVIS 11594

A WFC3 Grism Survey for Lyman Limit Absorption at z=2

We propose to conduct a spectroscopic survey of Lyman limit absorbers
at redshifts 1.8 z 2.5, using WFC3 and the G280 grism. This
proposal intends to complete an approved Cycle 15 SNAP program
(10878), which was cut short due to the ACS failure. We have selected
64 quasars at 2.3 z 2.6 from the Sloan Digital Sky Survey
Spectroscopic Quasar Sample, for which no BAL signature is found at
the QSO redshift and no strong metal absorption lines are present at z
2.3 along the lines of sight. The survey has three main

observational goals. First, we will determine the redshift frequency
dn/dz of the LLS over the column density range 16.0 log(NHI) 20.3
cm^-2. Second, we will measure the column density frequency
distribution f(N) for the partial Lyman limit systems (PLLS) over the
column density range 16.0 log(NHI) 17.5 cm^-2. Third, we will
identify those sightlines which could provide a measurement of the
primordial D/H ratio. By carrying out this survey, we can also help
place meaningful constraints on two key quantities of cosmological
relevance. First, we will estimate the amount of metals in the LLS
using the f(N), and ground based observations of metal line
transitions. Second, by determining f(N) of the PLLS, we can constrain
the amplitude of the ionizing UV background at z~2 to a greater
precision. This survey is ideal for a snapshot observing program,
because the on-object integration times are all well below 30 minutes,
and follow-up observations from the ground require minimal telescope
time due to the QSO sample being bright.

WFC3/IR 11591

Are Low-Luminosity Galaxies Responsible for Cosmic Reionization?

Our group has demonstrated that massive clusters, acting as powerful
cosmic lenses, can constrain 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. 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 blank field surveys, we propose a systematic
search through 10 lensing clusters with ACS/F814W and
WFC3/[F110W+F160W] (in conjunction with existing deep IRAC data). Our
goal is to measure with great accuracy the luminosity function at z~7
over a range of at least 3 magnitude, based on the identification of
about 50 lensed galaxies at 6.5z8. Our survey will mitigate cosmic
variance and extend the search both to lower luminosities and, by
virtue of the WFC3/IRAC combination, to higher redshift. Thanks to the
lensing amplification spectroscopic follow-up will be possible and
make our findings the most robust prior to the era of JWST and the
ELTs.

WFC3/ACS/UVIS/IR 11570

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.

STIS/CCD 11567

Boron Abundances in Rapidly Rotating Early-B Stars

Models of rotation in early-B stars predict that rotationally driven
mixing should deplete surface boron abundances during the
main-sequence lifetime of many stars. However, recent work has shown
that many boron depleted stars are intrinsically slow rotators for
which models predict no depletion should have occurred, while
observations of nitrogen in some more rapidly rotating stars show less
mixing than the models predict. Boron can provide unique information
on the earliest stages of mixing in B stars, but previous surveys have
been biased towards narrow- lined stars because of the difficulty in
measuring boron abundances in rapidly rotating stars. The two targets
observed as part of our Cycle 13 SNAP program 10175, just before STIS
failed, demonstrate that it is possible to make useful boron abundance
measurements for early-B stars with Vsin(i) above 100 km/s. We propose
to extend that survey to a large enough sample of stars to allow
statistically significant tests of models of rotational mixing in
early-B stars.

ACS/WFC3/SBC 11564

Optical and Ultraviolet Photometry of Isolated Neutron Stars

We propose ultraviolet and B-band observations of 5 nearby, thermally
emitting neutron stars. These data will measure the Rayleigh-Jeans
tails of their spectra, providing a vital complement to X-ray
spectroscopy and helping to constrain atmospheric models, working
toward the ultimate goal of unraveling the physics of neutron stars.
With these data we will have good-quality optical and UV data for the
full sample of these objects, allowing detailed comparisons between
them. Finally, the data should allow us to measure proper motions for
one or two objects, and will serve as the reference data for the
remaining objects; such proper motions allow ages to be determined for
these objects by tracing them back to likely birth locations.

WFC3/UV 11556

Investigations of the Pluto System

We propose a set of high SNR observations of the Pluto system that
will provide improved lightcurves, orbits, and photometric properties
of Nix and Hydra. The key photometric result for Nix and Hydra will be
a vastly improved lightcurve shape and rotation period to test if the
objects are in synchronous rotation or not. A second goal of this
program will be to retrieve a new epoch of albedo map for the surface
of Pluto. These observations will also improve masses and in some case
densities for the bodies in the Pluto system.

 




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