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NASA Hubble Space Telescope Daily Report #5175

Status Report From: Space Telescope Science Institute
Posted: Sunday, September 19, 2010

HUBBLE SPACE TELESCOPE - Continuing to Collect World Class Science

DAILY REPORT #5175

PERIOD COVERED: 5am September 3 - 5am September 7, 2010 (DOY 246/09:00z-249/09:00z)

FLIGHT OPERATIONS SUMMARY:

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

HSTARS:

12376 - GSAcq(1,2,1) scheduled at 246/17:10:16z required two attempts to achieve FL-DV on FGS-1.

Observations possibly affected: STIS 69 proposal ID#11668, ACS 77-78 proposal ID#11882

12377 - REAcq(1,2,1) Fails 2 Attempts, Fine Lock on 3rd Attempt @ 246/20:22z

Observations possibly affected: WFC3 170-171 proposal #11914, STIS 72 proposal #11668

12378 - GSAcq(2,1,1)scheduled at 248/03:04:13 resulted in fine lock backup on FGS2(2,0,2).

Observations possibly affected: ACS 104 proposal ID#11996, WFC3 234 and 235 proposal ID#11594, WFC3 2-3 proposal ID#11905

12381 ? GSAcq(1,2,1) Failed 1st Attempt, Fine lock on 2nd @ 249/12:16:37z

Observations possibly affected: STIS 9 proposal ID#11668

COMPLETED OPS REQUEST: (None)

COMPLETED OPS NOTES: (None)


SCHEDULED SUCCESSFUL
FGS GSAcq 28 28
FGS REAcq 33 33
OBAD with Maneuver 25 25


SIGNIFICANT EVENTS: (None)

OBSERVATIONS SCHEDULED:

WFC3/UV 12232

Detection and Mass Measurement of an Isolated Brown

We propose observations that are likely to detect the brown dwarf lens object for microlensing event MACHO-179-A, which was observed by the MACHO collaboration some 15 years ago. The strong microlensing parallax signal seen in the light curve and follow-up Keck adaptive optics images imply that the lens is a brown dwarf within about 300 parsecs. If the lens object is at least as massive as 0.015 Solar masses at an age of 1 Gyr or 0.03 Solar masses at an age of 10 Gyr, these observations will detect the lens and measure its relative lens-source proper motion. The relative proper motion can be combined with the microlensing parallax measurement and a precise WFC3/UVIS measurement of the source star brightness to yield a mass measurement of the source star to 3% or better.

WFC3/IR 12217

Spectroscopy of Faint T Dwarf Calibrators: Understanding the Substellar Mass Function and the Coolest Brown Dwarfs

More than 100 methane brown dwarfs, or T dwarfs, have now been discovered in the local field with 2MASS, SLOAN and UKIDSS, opening up a new area of physics describing objects at 450-1400 K. However, very few calibrator objects exist with well established ages and metallicities. A very surprising result from the UKIDSS sample (supported by 2MASS and SLOAN) is that the substellar mass function in the local field appears to decline to lower masses, in marked contrast to the rising initial mass function (IMF) observed in young clusters. Given that such a difference between the present day IMF and the Galactic time-averaged IMF is unlikely, it is very possible that the apparently falling IMF is an artifact of serious errors in either T model atmospheres or the evolutionary isochrones. We propose WFC3 spectroscopy of 4 faint T dwarf calibrators with well established ages and metallicities in the Pleiades and Sigma Ori clusters, and 2 faint field T dwarfs from UKIDSS for comparison. These spectra will constitute vital calibration data for T dwarf atmospheres with a wide range of surface gravities, which will be used to test and improve the model atmospheres. They will also aid preparation for future spectroscopy of the much larger numbers of field T dwarfs to soon be found by VISTA and WISE. These new surveys will permit a more precise measurement of the mass function and detection of even cooler objects.

WFC3/UV 12091

WFC3/UVIS Fringe Calibration - Part 2

Fringing has been observed in flat fields of 12 narrowband filters (4 full-frame and 3 quad spectral elements) longer than 600 nm, with peak-to-peak fringe amplitude variations ranging from 0.5% to 14.2% (WFC3 ISR 2010-04). Two filters (F953N and F656N) will be tested in program 11922, supporting 88 Cycle 17 GO exposures in these filters. Here we propose to observe globular cluster Omega Centauri (NGC 5139) in the other 10 filters affected by fringing, supporting 319 Cycle 17 GO exposures in these filters. By measuring the relative changes in brightness of stars at different positions on the detector, we will determine the local variations induced by the fringing pattern.

The data will serve two purposes: characterize the effect of fringing on photometry of on-orbit data, and verify models used to correct for fringing effects. The models rely on Thermal Vacuum Test 3 (TV3) data between 845-990 nm and NASA/GSFC Detector Characterization Laboratory (DCL) test data from 700-1060 nm. Only the F953N filter in program 11922 overlaps with the test data wavelength range, making it difficult to compare the efficacy of fringe models. This program will expand the on-orbit fringing data so that we can compare models at 6 new wavelengths within the ground test data wavelength range, as well as 4 new wavelengths not covered by the ground test data. Flight data in these 4 filters can be corrected by extrapolating the model beyond the wavelength range of the test data used to create the model.

COS/FUV 12083

COS G140L/1280 lamp template

This is an internal only program that obtains lamp template spectra with the G140L grating at all FPPOS, using the new cenwave 1280. This new cenwave will be available to users starting in Cycle 18. Data obtained in this program will be used to update the FUV lamp template reference file. We follow the same procedure following during SMOV when obtaining lamp template spectra, i.e., to allow any mechanism drift to settle the first exposure is 1800 sec long, with the lamp flashed at regular intervals.

Note that this program can only be executed after FSW changes have been made (current estimate for these FSW changes is ~Aug 2010 timeframe), as this mode is not yet implemented.

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.

COS/NUV/FUV 12034

COS-GTO: Brown Dwarf Activity Part 2

Based on the Findings in our Cycle 17 program, we will focus on M-stars in Cycle 18.

WFC3/UV 12019

After the Fall: Fading AGN in Post-starburst Galaxies

We propose joint Chandra and HST observations of an extraordinary sample of 12 massive post-starburst galaxies at z=0.4-0.8 that are in the short-lived evolution phase a few 100 Myr after the peak of merger-driven star formation and AGN activity. We will use the data to measure X-ray luminosities, black hole masses, and accretion rates; and with the accurate "clocks" provided by post-starburst stellar populations, we will directly test theoretical models that predict a power-law decay in the AGN light curve. We will also test whether star formation and black hole accretion shut down in lock-step, quantify whether the black holes transition to radiatively inefficient accretion states, and constrain the observational signatures of black hole mergers.

WFC3/UVIS 12018

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

There is growing observational and theoretical evidence to suggest that Ultra-Luminous X-ray sources (ULX) form preferentially in low metallicity environments. Here we propose a survey of 27 nearby (< 30Mpc) star-forming Extremely Metal Poor Galaxies (Z<5% solar). There are almost no X-ray observations of such low abundance galaxies (3 in the Chandra archive). These are the most metal-deficient galaxies known, and a logical place to find ULX if they favor metal-poor systems. We plan to test recent population synthesis models which predict that ULX should be very numerous in metal-poor galaxies. We will also test the hypothesis that ULX form in massive young star clusters, and ask for HST time to obtain the necessary imaging data.

WFC3/UV 12008

Primordial formation of Close Binaries in Globular Clusters with Low Density Cores

The primordial binary population is a key input parameter for any realistic model of dense star cluster dynamics. However, the number of primordial binaries and its direct implications for the formation rate of close binaries remain poorly understood. Theoretical calculations show that cataclysmic variables can be formed directly from primordial binaries in or near the core of low core density globular clusters. We propose to use Chandra/HST to study low density core globular clusters systematically and to test the prediction that low-luminosity X-ray sources can be formed from primordial binaries in the cluster core. This project will complement our successful Chandra/HST program to study the dynamical formation of X-ray sources in high core density globular clusters.

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/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 11928

WFC3/IR Low-Frequency Flat and Geometric Distortion

Multiple observations of globular cluster Omega Cen at multiple infrared wavelengths of IR detector will be used to derive filter dependency of low-frequency sensitivity (L_flat fields) across of IR detector and its time variation. Additionally, the same data will be also used to derive filter-dependant geometric distortion of the detector and its time-dependency.

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 11912

UVIS Internal Flats

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

WFC3/UVIS 11908

Cycle 17: UVIS Bowtie Monitor

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

WFC3/UVIS 11905

WFC3 UVIS CCD Daily Monitor

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

COS/FUV 11895

FUV Detector Dark Monitor

Monitor the FUV detector dark rate by taking long science exposures without illuminating the detector. The detector dark rate and spatial distribution of counts will be compared to pre-launch and SMOV data in order to verify the nominal operation of the detector. Variations of count rate as a function of orbital position will be analyzed to find dependence of dark rate on proximity to the SAA. Dependence of dark rate as function of time will also be tracked.

COS/NUV 11894

NUV Detector Dark Monitor

The purpose of this proposal is to measure the NUV detector dark rate by taking long science exposures with no light on the detector. The detector dark rate and spatial distribution of counts will be compared to pre-launch and SMOV data in order to verify the nominal operation of the detector. Variations of count rate as a function of orbital position will be analyzed to find dependence of dark rate on proximity to the SAA. Dependence of dark rate as function of time will also be tracked.

ACS/WFC3 11882

CCD Hot Pixel Annealing

This program continues the monthly anneal that has taken place every four weeks for the last three cycles. We now obtain WFC biases and darks before and after the anneal in the same sequence as is done for the ACS daily monitor (now done 4 times per week). So the anneal observation supplements the monitor observation sets during the appropriate week. Extended Pixel Edge Response (EPER) and First Pixel Response (FPR) data will be obtained over a range of signal levels for the Wide Field Channel (WFC). This program emulates the ACS pre-flight ground calibration and post-launch SMOV testing (program 8948), so that results from each epoch can be directly compared. The High Resolution Channel (HRC) visits have been removed since it could not be repaired during SM4.

This program also assesses the read noise, bias structure, and amplifier cross-talk of ACS/WFC using the GAIN=1.4 A/D conversion setting. This investigation serves as a precursor to a more comprehensive study of WFC performance using GAIN=1.4.

STIS/CCD 11849

STIS CCD Hot Pixel Annealing

This purpose of this activity is to repair radiation induced hot pixel damage to the STIS CCD by warming the CCD to the ambient instrument temperature and annealing radiation-damaged pixels.

Radiation damage creates hot pixels in the STIS CCD Detector. Many of these hot pixels can be repaired by warming the CCD from its normal operating temperature near -83 deg. C to the ambient instrument temperature (~ +5 deg. C) for several hours. The number of hot pixels repaired is a function of annealing temperature. The effectiveness of the CCD hot pixel annealing process is assessed by measuring the dark current behavior before and after annealing and by searching for any window contamination effects.

STIS/CCD 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/CCD 11845

CCD Dark Monitor Part 2

Monitor the darks for the STIS CCD.

STIS/CCD 11740

A Complete Optical and NIR Atmospheric Transmission Spectrum of the Exoplanet

The hot Jupiter HD189733b offers the best exoplanet in which to perform atmospheric studies through transit spectroscopy. Here we propose STIS and Nicmos spectra to help construct a full exoplanetary transit transmission spectrum that extends over the entire optical and near-infrared range. Such a spectrum will link existing observed atmospheric features such as haze, water, and methane, providing a coherent understanding of all these reported features. With a spectrum covering many observed absorption features, the absolute pressure scale and abundances can be determined linking observed features to the actual atmospheric properties of the exoplanet.

WFC3/IR 11738

SPIDERWEBS AND FLIES: OBSERVING MASSIVE GALAXY FORMATION IN ACTION

Distant luminous radio galaxies are among the brightest known galaxies in the early Universe, pinpoint likely progenitors of dominant cluster galaxies and are unique laboratories for studying massive galaxy formation. Spectacular images with the ACS and NICMOS of one such object, the "Spiderweb Galaxy" at z = 2.2, show in exquisite detail, hierarchical merging occurring 11 Gyr ago. By imaging 3 additional Spiderweb-like galaxies we wish to study this potentially crucial phase of massive galaxy evolution, when hierarchical merging, galaxy downsizing and AGN feedback are all likely to be occurring. Properties of the complete sample of Spiderweb galaxies will be used to (i) constrain models for the formation and evolution of the most massive galaxies that dominate rich clusters and (ii) investigate the nature of chain and tadpole galaxies, a fundamental but poorly understood constituent of the early Universe.

We shall image rest-frame UV and optical continuum emission from 3 radio galaxies with 2.4 < z < 3.8 that appear clumpy and large in shallow WFPC/PC observations. The new observations will typically reach ~2 magnitudes fainter over 20-40 times larger area than previously. Photometric and morphological parameters will be measured for satellite galaxies ("flies") in the clumpy massive hosts and for galaxies in ~ 1.5 Mpc x 1.5 Mpc regions of surrounding protoclusters. Locations, sizes, elongations, clumpiness, masses, and star formation rates of the merging satellite and protocluster galaxies will be compared with new state of the art simulations. Combination of ACS and WFC3 images will help disentangle the properties of the young and old populations.

Specific goals include: (i) investigating star formation histories of the satellite galaxies and the extended emission, (ii) studying "downsizing" and merging scenarios and (iii) measuring the statistics of linear galaxies and relating them to models for the formation of massive galaxies and to the properties of the important but enigmatic class of chain/tadpole galaxies in the HUDF.

STIS/CCD 11721

Verifying the Utility of Type Ia Supernovae as Cosmological Probes: Evolution and Dispersion in the Ultraviolet Spectra

The study of distant type Ia supernova (SNe Ia) offers the most practical and immediate discriminator between popular models of dark energy. Yet fundamental questions remain over possible redshift-dependent trends in their observed and intrinsic properties. High-quality Keck spectroscopy of a representative sample of 36 intermediate redshift SNe Ia has revealed a surprising, and unexplained, diversity in their rest-frame UV fluxes. One possible explanation is hitherto undiscovered variations in the progenitor metallicity. Unfortunately, this result cannot be compared to local UV data as only two representative SNe Ia have been studied near maximum light. Taking advantage of two new `rolling searches' and the restoration of STIS, we propose a non-disruptive TOO campaign to create an equivalent comparison local sample. This will allow us to address possible evolution in the mean UV spectrum and its diversity, an essential precursor to the study of SNe beyond z~1.

WFC3/UVIS 11714

Snapshot Survey for Planetary Nebulae in Local Group Globular Clusters

Planetary nebulae (PNe) in globular clusters (GCs) raise a number of interesting issues related to stellar and galactic evolution. The number of PNe known in Milky Way GCs, four, is surprisingly low if one assumes that all stars pass through a PN stage. However, it is likely that the remnants of stars now evolving in galactic GCs leave the AGB so slowly that any ejected nebula dissipates long before the star becomes hot enough to ionize it. Thus there should not be ANY PNe in Milky Way GCs--but there are four! It has been suggested that these Pne are the result of mergers of binary stars within GCs, i.e., that they are descendants of blue stragglers. The frequency of occurrence of PNe in external galaxies poses more questions, because it shows a range of almost an order of magnitude.

I propose a SNAPshot survey aimed at discovering PNe in the GC systems of Local Group galaxies outside the Milky Way. These clusters, some of which may be much younger than their counterparts in our galaxy, might contain many more PNe than those of our own galaxy. I will use the standard technique of emission-line and continuum imaging, which easily discloses PNe. This proposal continues a WFPC2 program started in Cycle 16, but with the more powerful WFC3. As a by-product, the survey will also produce color-magnitude diagrams for numerous clusters for the first time, reaching down to the horizontal branch.

STIS/CCD/MA 11668

Cosmo-chronometry and Elemental Abundance Distribution of the Ancient Star HE1523-0901

We propose to obtain near-UV HST/STIS spectroscopy of the extremely metal-poor, highly r-process-enhanced halo star HE 1523-0901, in order to produce the most complete abundance distribution of the heaviest stable elements, including platinum, osmium, and lead. These HST abundance data will then be used to estimate the initial abundances of the long-lived radioactive elements thorium and uranium, and by comparison with their observed abundances, enable an accurate age determination of this ancient star. The use of radioactive chronometers in stars provides an independent lower limit on the age of the Galaxy, which can be compared with alternative limits set by globular clusters and by analysis from WMAP. Our proposed observations of HE1523-0901 will also provide significant new information about the early chemical history of the Galaxy, specifically, the nature of the first generations of stars and the types of nucleosynthetic processes that occurred at the onset of Galactic chemical evolution.

COS/NUV/ACS/WFC/FUV 11658

Probing the Outer Regions of M31 with QSO Absorption Lines

We propose HST-COS spectroscopy of 10 quasars behind M31. Absorption lines due to MgII, FeII, CIV, and a variety of other lines will be searched for and measured. Six quasars lie between 1 and 4.2 Holmberg radii near the major axis on the southwest side, where confusion with Milky Way gas is minimized. Two lie even farther out on the southwest side of the major axis. One lies within 1 Holmberg radius. Two of the 10 pass through M31's high velocity clouds seen in a detailed 21 cm emission map. Exposure time estimates were based on SDSS magnitudes and available GALEX magnitudes. Thus, using the most well-studied external spiral galaxy in the sky, our observations will permit us to check, better than ever before, the standard picture that quasar metal-line absorption systems such as MgII and CIV arise in an extended gaseous halo/disk of a galaxy well beyond its observable optical radius. The observations will yield insights into the nature of the gas and its connection to the very extended stellar components of M31 that have recently been studied. Notably the observations have the potential of extending M31's rotation curve to very large galactocentric distances, thereby placing new constraints on M31's dark matter halo.

Finally, we also request that the coordinated parallel orbits be allocated to this program so that we may image the resolved stellar content of M31's halo and outer disk.

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.

STIS/CCD 11626

Searching for the Upper Mass Limit in NGC 3603, the Nearest Giant H II Region

What is the mass of the highest mass star? 100Mo? 150Mo? 200Mo? Or higher? Theory gives us little guidance as to what physics sets the upper mass limit, presuming one exists. Is it due to limitations in the highest masses that can coalesce? Or is it due to stability issues in such a behemoth? Observationally, the upper mass limit is poorly constrained at present, with the strongest evidence coming from the K-band luminosity function of the Arches cluster near the Galactic Center. Here we propose to investigate this question by determining the Initial Mass Function of NGC 3603, the nearest giant H II region. This cluster is known to contain a wealth of O3 and hydrogen-rich Wolf-Rayets, the most luminous and massive of stars. By constructing an accurate H-R diagram for the cluster, we will construct a present day mass function using newly computed high mass evolutionary tracks, and convert this to an initial mass function using the inferred ages. This will allow us to see whether or not there is a true deficit of high mass stars, evidence of an upper mass cutoff. At the same time we are likely to establish good masses for the highest mass stars ever determined. We have laid the groundwork for this project using the Magellan 6.5-m telescope and the excellent seeing found on Las Campanas, plus analysis of archival ACS/HRS frames, but we now need to obtain spectra of the stars unobservable from the ground. This can only be done with HST and a refurbished STIS.

ACS/WFC3 11599

Distances of Planetary Nebulae from SNAPshots of Resolved Companions

Reliable distances to individual planetary nebulae (PNe) in the Milky Way are needed to advance our understanding of their spatial distribution, birthrates, influence on galactic chemistry, and the luminosities and evolutionary states of their central stars (CSPN). Few PNe have good distances, however. One of the best ways to remedy this problem is to find resolved physical companions to the CSPN and measure their distances by photometric main- sequence fitting. We have previously used HST to identify and measure probable companions to 10 CSPN, based on angular separations and statistical arguments only. We now propose to use HST to re-observe 48 PNe from that program for which additional companions are possibly present. We then can use the added criterion of common proper motion to confirm our original candidate companions and identify new ones in cases that could not confidently be studied before. We will image the region around each CSPN in the V and I bands, and in some cases in the B band. Field stars that appear close to the CSPN by chance will be revealed by their relative proper motion during the 13+ years since our original survey, leaving only genuine physical companions in our improved and enlarged sample. This study will increase the number of Galactic PNe with reliable distances by 50 percent and improve the distances to PNe with previously known companions.

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/UVIS 11588

Galaxy-Scale Strong Lenses from the CFHTLS Survey

We aim to investigate the origin and evolution of early-type galaxies using gravitational lensing, modeling the mass profiles of objects over a wide range of redshifts. The low redshift (z = 0.2) sample is already in place following the successful HST SLACS survey; we now propose to build up and analyze a sample of comparable size (~50 systems) at high redshift (0.4 < z < 0.9) using HST WFC3 Snapshot observations of lens systems identified by the SL2S collaboration in the CFHT legacy survey.

WFC3/ACS/IR 11563

Galaxies at z~7-10 in the Reionization Epoch: Luminosity Functions to <0.2L* from Deep IR Imaging of the HUDF and HUDF05 Fields

The first generations of galaxies were assembled around redshifts z~7-10+, just 500-800 Myr after recombination, in the heart of the reionization of the universe. We know very little about galaxies in this period. Despite great effort with HST and other telescopes, less than ~15 galaxies have been reliably detected so far at z>7, contrasting with the ~1000 galaxies detected to date at z~6, just 200-400 Myr later, near the end of the reionization epoch. WFC3 IR can dramatically change this situation, enabling derivation of the galaxy luminosity function and its shape at z~7-8 to well below L*, measurement of the UV luminosity density at z~7-8 and z~8-9, and estimates of the contribution of galaxies to reionization at these epochs, as well as characterization of their properties (sizes, structure, colors). A quantitative leap in our understanding of early galaxies, and the timescales of their buildup, requires a total sample of ~100 galaxies at z~7-8 to ~29 AB mag. We can achieve this with 192 WFC3 IR orbits on three disjoint fields (minimizing cosmic variance): the HUDF and the two nearby deep fields of the HUDF05. Our program uses three WFC3 IR filters, and leverages over 600 orbits of existing ACS data, to identify, with low contamination, a large sample of over 100 objects at z~7-8, a very useful sample of ~23 at z~8-9, and limits at z~10. By careful placement of the WFC3 IR and parallel ACS pointings, we also enhance the optical ACS imaging on the HUDF and a HUDF05 field. We stress (1) the need to go deep, which is paramount to define L*, the shape, and the slope alpha of the luminosity function (LF) at these high redshifts; and (2) the far superior performance of our strategy, compared with the use of strong lensing clusters, in detecting significant samples of faint z~7-8 galaxies to derive their luminosity function and UV ionizing flux. Our recent z~7.4 NICMOS results show that wide-area IR surveys, even of GOODS-like depth, simply do not reach faint enough at z~7-9 to meet the LF and UV flux objectives. In the spirit of the HDF and the HUDF, we will waive any proprietary period, and will also deliver the reduced data to STScI. The proposed data will provide a Legacy resource of great value for a wide range of archival science investigations of galaxies at redshifts z~2- 9. The data are likely to remain the deepest IR/optical images until JWST is launched, and will provide sources for spectroscopic follow up by JWST, ALMA and EVLA.

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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