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 z>6. 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

z>2.73 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

6.5<z<8.8 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 z>6 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 are: (1) Detect Lya

in ~100 galaxies with z>5.6 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 0.5<z<1.8 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

0.5<z<2.2; 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

6.5<z<8. 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.