HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science



DAILY REPORT #5145



PERIOD COVERED: 5am July 23 - 5am July 26, 2010 (DOY 204/09:00z-207/09:00z)



FLIGHT OPERATIONS SUMMARY:



Significant Spacecraft Anomalies: (The following are preliminary reports

of potential non-nominal performance that will be investigated.)



HSTARS:

12337 - REAcq(2,1,1) scheduled at 205/09:14:55z failed to RGA control at 205/09:21:09z.



Observations affected: ACS 102-107 Proposal ID# 11887, WFC3 202 Proposal ID# 11905,

WFC3 203-204 Proposal ID# 11929.



COMPLETED OPS REQUEST: (None)



COMPLETED OPS NOTES: (None)



SCHEDULED SUCCESSFUL

FGS GSAcq 22 22

FGS REAcq 21 20

OBAD with Maneuver 22 22



SIGNIFICANT EVENTS: (None)



OBSERVATIONS SCHEDULED:



WFC3/UV/ACS/WFC/IR 12058



A Panchromatic Hubble Andromeda Treasury - I



We propose to image the north east quadrant of M31 to deep limits in the

UV, optical, and near-IR. HST imaging should resolve the galaxy into

more than 100 million stars, all with common distances and foreground

extinctions. UV through NIR stellar photometry (F275W, F336W with

WFC3/UVIS, F475W and F814W with ACS/WFC, and F110W and F160W with

WFC3/NIR) will provide effective temperatures for a wide range of

spectral types, while simultaneously mapping M31's extinction. Our

central science drivers are to: understand high-mass variations in the

stellar IMF as a function of SFR intensity and metallicity; capture the

spatially-resolved star formation history of M31; study a vast sample of

stellar clusters with a range of ages and metallicities. These are

central to understanding stellar evolution and clustered star formation;

constraining ISM energetics; and understanding the counterparts and

environments of transient objects (novae, SNe, variable stars, x-ray

sources, etc.). As its legacy, this survey adds M31 to the Milky Way and

Magellanic Clouds as a fundamental calibrator of stellar evolution and

star-formation processes for understanding the stellar populations of

distant galaxies. Effective exposure times are 977s in F275W, 1368s in

F336W, 4040s in F475W, 4042s in F814W, 699s in F110W, and 1796s in

F160W, including short exposures to avoid saturation of bright sources.

These depths will produce photon-limited images in the UV. Images will

be crowding-limited in the optical and NIR, but will reach below the red

clump at all radii. The images will reach the Nyquist sampling limit in

F160W, F475W, and F814W.



S/C 12046



COS FUV DCE Memory Dump



Whenever the FUV detector high voltage is on, count rate and current

draw information is collected, monitored, and saved to DCE memory. Every

10 msec the detector samples the currents from the HV power supplies

(HVIA, HVIB) and the AUX power supply (AUXI). The last 1000 samples are

saved in memory, along with a histogram of the number of occurrences of

each current value.



In the case of a HV transient (known as a "crackle" on FUSE), where one

of these currents exceeds a preset threshold for a persistence time, the

HV will shut down, and the DCE memory will be dumped and examined as

part of the recovery procedure. However, if the current exceeds the

threshold for less than the persistence time (a "mini-crackle" in FUSE

parlance), there is no way to know without dumping DCE memory. By

dumping and examining the histograms regularly, we will be able to

monitor any changes in the rate of "mini-crackles" and thus learn

something about the state of the detector.



WFC3/IR 12005



Unveiling the Dusty Starburst Galaxy Hosting GRB080607



GRB 080607 at redshift z = 3.0363 is a unique case of a highly

extinguished (A_V ~ 3 mag) afterglow that was yet sufficiently bright

for high-quality spectroscopy. The ISM properties revealed by our

afterglow spectrum are unprecedented among GRB host galaxies, including

an enormous dust and gas surface mass density (~ 400 M_sun/pc^2), the

first detection of CO molecules, and roughly solar metallicity. Contrary

to the common expectation of GRBs occurring preferentially in low-mass

and low-metallicity environments, the observed large metal and dust

content, together with the mass-metallicity relation known for z=2-3

galaxies, imply that the host galaxy is massive and intrinsically

luminous. Identifying the host galaxy of this event is critical for

connecting our spectroscopy to the rest of the poorly-understood dark

burst population with suppressed optical afterglow light. Despite our

large investments in optical and NIR imaging at ground-based telescopes

to date, the host of GRB 080607 has eluded detection to an unobscured

limiting UV luminosity of ~ 0.07 L*. The lack of bright emission

suggests that the dust seen in the afterglow spectrum reflects the

global dust content throughout the host ISM. Otherwise, it would imply

the presence of highly metal-enriched regions in a low-mass galaxy,

challenging the validity of our current understanding of star formation

at high redshift.



The low sky background and high spatial resolution make HST and WFC3/IR

the only instrument available to unveil the morphology and stellar

counterpart of the dusty host galaxy of GRB 080607. Here we request

Director's Discretionary time to obtain deep near-infrared images of the

field surrounding GRB 080607, using WFC3 and the IR channel with the

F160W filter. The proposed imaging program will allow us to investigate

whether the host of GRB 080607 is a dusty luminous galaxy or a faint

dwarf galaxy with patchy dust clouds, and to examine the significance of

dust enshrouded star formation at z~3.



The extraordinary ISM properties observed around GRB 080607 have

stimulated a considerable amount of interest not only in the GRB

community but also among observers and theorists who study star

formation both in the nearby universe and at high redshift. We believe

the proposed WFC3/IR imaging data will have high impact in the broader

astrophysics community.



ACS/WFC 11996



CCD Daily Monitor (Part 3)



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 308 orbits (19.25 weeks) from 21 June 2010 to 1 November

2010.



WFC3/IR 11933



IR Rate Dependent Non-linearity



The NICMOS non-linearity known as the Bohlin Effect has revealed that

the apparent flux of a source observed by NICMOS is not a simple, linear

function of count rate. The effect has been characterized by

observations of star clusters observed with and without additional

background from the internal lamps. As WFC3 lacks internal lamps which

can be used to add background, we will rely on the bright Earth limb to

provide additional background. We will observe a star cluster, 47 Tuc,

repeatedly throughout a complete HST orbit which has been chosen to put

the closest approach to the bright Earth to be 13.5 degrees, the closest

approach allowed while retaining FGS guiding. Another set will be done

with the BE limb closest approach of 15.5 degrees. The observations will

be done with the two most commonly used filters, F110W and F160W and at

two different bright Earth limb angles to test the linearity of the

non-linearity. We have also included an orbit on NGC 1850 to repeat the

NICMOS field for which the linearity of the field has been established.



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 11917



IR Earth Flats Pathfinder



This program is an experimental path finder for Cycle 18 calibration.

(The WFC3 UVIS version of this is program 11914 and contains additional

detail in its description). Infrared-wavelength flat fields will be

obtained by observing the dark side of the Earth during periods of full

moon illumination. The observations will consist of full-frame streaked

WFC3 IR imagery: per single "dark-sky" orbit, we anticipate achieving

Poisson S/N > 100 per pixel in each of three to five exposures,

depending on sample sequence (SPARS25 or SPARS50).



Why not use the Sunlit Earth? It is too bright for WFC3 IR full-frame

minimum exposure time of 3 sec. Similarly, for NICMOS the sunlit-Earth

is too bright which saturates the detector too quickly and/or induces

abnormal behaviors such as super-shading (Gilmore 1998, NIC 098-011). In

the narrowband IR filters the sunlit earth sometimes is faint enough to

not saturate immediately, but based upon predictions (Cox et al. 1987

"Standard Astronomical Sources for HST: 6. Spatially Flat Fields.") and

observations (Gilmore 1998), we consider sunlit Earth unlikely to be

successful unless it is twilight.



Other possibilities? Cox et al.'s Section II.D addresses many other

possible sources for flat fields, rejecting them for a variety of

reasons. A remaining possibility would be the totally eclipsed moon.

Such eclipses provide approximately 2 hours (1 HST orbit) of opportunity

per year, so they are too rare to be generically useful. An advantage of

the moon over the Earth is that the moon subtends less than 0.25 square

degree, whereas the Earth subtends a steradian or more, so scattered

light and light prior to the unshuttered exposure presents additional

problems for the Earth. Also, we're unsure if HST can point 180 deg from

the Sun.



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 11914



UVIS Earth Flats



This program is an experimental path finder for Cycle 18 calibration.

Visible-wavelength flat fields will be obtained by observing the dark

side of the Earth during periods of full moon illumination. The

observations will consist of full-frame streaked WFC3 UVIS imagery: per

22-min total exposure time in a single "dark-sky" orbit, we anticipate

collecting 7000 e/pix in F606W or 4500 e/pix in F814W. To achieve

Poisson S/N > 100 per pixel, we require at least 2 orbits of F606W and 3

orbits of F814W.



For UVIS narrowband filters, exposures of 1 sec typically do not

saturate on the sunlit Earth, so we will take sunlit Earth flats for

three of the more-commonly used narrowband filters in Cycle 17 plus the

also-popular long-wavelength quad filters, for which we get four filters

at once.



Why not use the Sunlit Earth for the wideband visible-light filters? It

is too bright in the visible for WFC3 UVIS minimum exposure time of 0.5

sec. Similarly, for NICMOS the sunlit-Earth is too bright which

saturates the detector too quickly and/or induces abnormal behaviors

such as super- shading (Gilmore 1998, NIC 098-011). In the narrowband

visible and broadband near-UV its not too bright (predictions in Cox et

al. 1987 "Standard Astronomical Sources for HST: 6. Spatially Flat

Fields." and observations in ACS Program 10050).



Other possibilities? Cox et al.'s Section II.D addresses many other

possible sources for flat fields, rejecting them for a variety of

reasons. A remaining possibility would be the totally eclipsed moon.

Such eclipses provide approximately 2 hours (1 HST orbit) of opportunity

per year, so they are too rare to be generically useful. An advantage of

the moon over the Earth is that the moon subtends less than 0.25 square

degree, whereas the Earth subtends a steradian or more, so scattered

light and light potentially leaking around the shutter presents

additional problems for the Earth. Also, we're unsure if HST can point

180 deg from the Sun.



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).



ACS/WFC3 11887



CCD Stability Monitor



This program will verify that the low frequency flat fielding, the

photometry, and the geometric distortion are stable in time and across

the field of view of the CCD arrays. A moderately crowded stellar field

in the cluster 47 Tuc is observed with the ACS (at the cluster core) and

WFC3 (6 arcmin West of the cluster core) using the full suite of broad

and narrow band imaging filters. The positions and magnitudes of objects

will be used to monitor local and large scale variations in the plate

scale and the sensitivity of the detectors and to derive an independent

measure of the detector CTE. The UV sensitivity for the SBC and ACS will

be addressed in the UV contamination monitor program (11886, PI=Smith).



One additional orbit will be obtained at the beginning of the cycle will

allow a verification of the CCD gain ratios for WFC3 using gain 2.0,

1.4, 1.0, 0.5 and for ACS using gain 4.0 and 2.0. In addition, one

subarray exposure with the WFC3 will allow a verification that

photometry obtained in full-frame and in sub-array modes are repeatable

to better than 1%. This test is important for the ACS Photometric

Cross-Calibration program (11889, PI=Bohlin) which uses sub-array

exposures.



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.



ACS/WFC3 11735



The LSD Project: Dynamics, Merging and Stellar Populations of a Sample

of Well-Studied LBGs at z~3



A large observational effort with the ground-based ESO/VLT telescopes

allowed us to obtain deep, spatially-resolved, near-IR spectra of

complete sample of 11 Lyman-Break Galaxies at z~3.1. These observations

were used to obtain, for the first time, the metallicity and the

dynamical properties of a sample of objects that, albeit small, is

representative of the total population of the LBGs. We propose to use

HST to obtain high-resolution optical and near-IR images of this sample

of LBGs in order to study the broad-band morphology and the stellar

light distribution of these galaxies. These images, exploiting the

superior spatial resolution of HST images and the low-background : 1-

will allow a precise measure of the dynamical mass from the velocity

field derived with spectroscopy; 2- will permit a comparison of the

distribution of star formation (from the line emission) with the

underlying stellar population, and, 3- will be used to check if the

complex velocity field and the multiple line-emitting regions detected

in most targets can be ascribed to on-going mergers. This accurate study

will shed light on a number of unsolved problems still affecting the

knowledge of the LBGs.



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.



WFC3/UVIS 11730



Continued Proper Motions of the Magellanic Clouds: Orbits, Internal

Kinematics, and Distance



In Cycles 11 and 13 we obtained two epochs of ACS/HRC data for fields in

the Magellanic Clouds centered on background quasars. We used these data

to determine the proper motions of the LMC and SMC to better than 5% and

15% respectively. The results had a number of unexpected implications

for the Milky Way-LMC-SMC system and received considerable attention in

the literature and in the press. The implied three-dimensional

velocities are larger than previously believed and close to the escape

velocity in a standard 10^12 solar mass Milky Way dark halo. Our orbit

calculations suggest the Clouds may not be bound to the Milky Way or may

just be on their first passage, both of which are unexpected in view of

traditional interpretations of the Magellanic Stream. Alternatively, the

Milky Way dark halo may be a factor two more massive than previously

believed, which would be surprising in view of other observational

constraints. Also, the relative velocity between the LMC and SMC was

larger than expected, leaving open the possibility that the Clouds may

not be bound to each other. To further verify and refine our results we

requested an additional epoch data in Cycle 16 which is being executed

with WFPC2/PC due to the failure of ACS. A detailed analysis of one LMC

field shows that the field proper motion using all three epochs of data

is consistent within 1-sigma with the two- epoch data, thus verifying

that there are no major systematic effects in our previous measurements.

The random errors, however, are only smaller by a factor of 1.4 because

of the relatively large errors in the WFPC2 data. A prediction for a

fourth epoch with measurement errors similar to epochs 1 and 2 shows

that the uncertainties will improve by a factor of 3. This will allow us

to better address whether the Clouds are indeed bound to each other and

to the Milky Way. It will also allow us to constrain the internal

motions of various populations within the Clouds, and to determine a

distance to the LMC using rotational parallax. Continuation of this

highly successful program is therefore likely to provide important

additional insights. Execution in SNAPshot mode guarantees maximally

efficient use of HST resources.



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/UVIS 11657



The Population of Compact Planetary Nebulae in the Galactic Disk



We propose to secure narrow- and broad-band images of compact planetary

nebulae (PNe) in the Galactic Disk to study the missing link of the

early phases of post-AGB evolution. Ejected AGB envelopes become PNe

when the gas is ionized. PNe expand, and, when large enough, can be

studied in detail from the ground. In the interim, only the HST

capabilities can resolve their size, morphology, and central stars. Our

proposed observations will be the basis for a systematic study of the

onset of morphology. Dust properties of the proposed targets will be

available through approved Spitzer/IRS spectra, and so will the

abundances of the alpha- elements. We will be able thus to explore the

interconnection of morphology, dust grains, stellar evolution, and

populations. The target selection is suitable to explore the nebular and

stellar properties across the galactic disk, and to set constraints on

the galactic evolutionary models through the analysis of metallicity and

population gradients.



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/UVIS 11643



A Timeline for Early-Type Galaxy Formation: Mapping the Evolution of

Star Formation, Globular Clusters, Dust, and Black Holes



While considerable effort has been devoted to statistical studies of the

origin of the red sequence of galaxies, there has been relatively little

direct exploration of galaxies transforming from late to early types.

Such galaxies are identified by their post-starburst spectra, bulge-

dominated, tidally-disturbed morphologies, and current lack of gas. We

are constructing the first detailed timeline of their evolution onto the

red sequence, pinpointing when star formation ends, nuclear activity

ceases, globular clusters form, and the bulk of the merging progenitors'

dust disappears. Here we propose to obtain HST and Chandra imaging of

nine galaxies, whose wide range of post-starburst ages we have precisely

dated with a new UV-optical technique and for which we were awarded

Spitzer time. We will address 1) whether the black hole-bulge mass

relation arises from nuclear feedback, 2) whether the bimodality of

globular cluster colors is due to young clusters produced in galaxy

mergers, and 3) what happens to the dust when late types merge to form

an early type.



WFC3/IR 11631



Binary Brown Dwarfs and the L/T Transition



Brown dwarfs traverse spectral types M, L and T as their atmospheric

structure evolves and they cool into oblivion. This SNAPSHOT program

will obtain WFC3-IR images of 45 nearby late-L and early-T dwarfs to

investigate the nature of the L/T transition. Recent analyses have

suggested that a substantial proportion of late-L and early-T dwarfs are

binaries, comprised of an L dwarf primary and T dwarf secondary. WFC3-IR

observations will let us quantify this suggestion by expanding coverage

to a much larger sample, and permitting comparison of the L/T binary

fraction against �normal� ultracool dwarfs. Only eight L/T binaries are

currently known, including several that are poorly resolved: we

anticipate at least doubling the number of resolved systems. The

photometric characteristics of additional resolved systems will be

crucial to constraining theoretical models of these late-type ultracool

dwarfs. Finally, our data will also be eminently suited to searching for

extremely low luminosity companions, potentially even reaching the Y

dwarf regime.



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.



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.