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.
Photometric Metallicity Calibration with WFC3 Specialty Filters
The community has chosen to include several filters in the WFC3 filter complement that have been designed to allow fairly precise estimates of stellar metallicities, and many science programs are enabled by this capability. Since these filters do not exactly match those used for this purpose on the ground, however, the mapping of stellar colors to stellar metallicities needs to be calibrated. We propose to achieve this calibration through observations of five stellar clusters with well known metallicities. We will calibrate several different filter calibrations which will allow future users to determine what filter combination best meets their science needs.
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.
The Nuclear Structure of OH Megamaser Galaxies
We propose a snapshot survey of a complete sample of 80 OH megamaser galaxies. Each galaxy will be imaged with the ACS/WFC through F814W and a linear ramp filter (FR656N or FR716N or FR782N or FR853N) allowing us to study both the spheroid and the gas morphology in Halpha + [N II]. We will use the 9% ramps FR647M (5370-7570 angstroms) centered at 7000 angstroms and FR914M (7570-10, 719 angstroms) 8000 angstroms for continuum subtraction for the high and low z objects respectively. OH megamaser galaxies (OHMG) form an important class of ultraluminous IR-galaxies (ULIRGs) whose maser lines emit QSO-like luminosities. ULIRGs in general are associated with recent mergers but it is often unclear whether their power output is dominated by starbursts or a hidden QSO because of the high absorbing columns which hide their nuclei even at X-ray wavelengths. In contrast, OHMG exhibit strong evidence for the presence of an energetically important and recently triggered active nucleus. In particular it is clear that much of the gas must have already collapsed to form a nuclear disk which may be the progenitor of a circum-nuclear torus, a key element of the unified scheme of AGN. A great advantage of studying OHMG systems over the general ULIRG population, is that the circum-nuclear disks are effectively "fixed" at an inner, edge on, orientation, eliminating varying inclination as a nuisance parameter. We will use the HST observations in conjunction with existing maser and spectroscopic data to construct a detailed picture of the circum-nuclear regions of a hitherto relatively neglected class of galaxy that may hold the key to understanding the relationship between galaxy mergers, nuclear star- formation, and the growth of massive black holes and the triggering of nuclear activity.
COS-GTO: Search for Hydrocarbons and Nitriles in Pluto's Atmosphere
Methane is highly abundant in Pluto's atmosphere, and methane photolysis is the starting point for a series of chemical processes that should result in the production of hydrocarbons and nitriles. Photochemical modeling of Pluto's atmosphere has suggested that detectable abundances of various hydrocarbons and nitriles should occur on Pluto. However, past analysis of 40 orbits of archival HST/FOS data in the mid-UV has only produced upper limits on abundances of C4H2, C6H2, HC3N, and C4N2. We will use COS to obtain spectra from 2060-2460A, including absorption bands of the hydrocarbon diacetylene (C4H2) and the nitrile cyanoacetylene (HC3N). Previously-measured 2-sigma upper limits for these compounds are somewhat below the values computed in the poorly-constrained models; the measurement uncertainties themselves are of the same order as the modeled values. By reducing the uncertainties by a factor of a few to several, we aim to detect the presence of these compounds, or to provide more restrictive abundance limits. These measurements will provide valuable new data on the nature and chemistry of the Plutonian atmosphere.
CCD Dark Monitor Part 2
Monitor the darks for the STIS CCD.
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.
MAMA NUV Flats
This program will obtain NUV-MAMA observations of the STIS internal Deuterium lamp to construct an NUV flat applicable to all NUV modes.
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.
A Deep Exploration of Classes of Long Period Variable Stars in M31
We propose a thrifty but information-packed investigation with WFC3/IR F160W and F110W providing crucial information about Long Period Variables in M31, at a level of detail that has recently allowed the discovery of new variable star classes in the Magellanic Clouds, a very different stellar population. These observations are buttressed by an extensive map of the same fields with ACS and WFC3 exposures in F555W and F814W, and a massive ground- based imaging patrol producing well-sampled light curves for more than 400,000 variable stars. Our primary goal is to collect sufficient NIR data in order to analyze and classify the huge number of long-period variables in our catalog (see below) through Period Luminosity (P/L) diagrams. We will produce accurate P/L diagrams for both the bulge and a progression of locations throughout the disk of M31. These diagrams will be similar in quality to those currently in the Magellanic Clouds, with their lower metallicity, radically different star formation history, and larger spread in distance to the variables. M31 offers an excellent chance to study more typical disk populations, in a manner which might be extended to more distant galaxies where such variables are still visible, probing a much more evenly spread progenitor age distribution than cepheids (and perhaps useful as a distance scale alternative or cross- check). Our data will also provide a massive and unique color-magnitude dataset; we expect that this study will produce several important results, among them a better understanding of P/L and P/L-color relations for pulsating variables which are essential to the extragalactic distance ladder. We will view these variables at a common distance over a range of metallicities (eliminating the distance-error vs. metallicity ambiguity between the LMC and SMC), allow further insight into possible faint-variable mass-loss for higher metallicities, and in general produce a sample more typical of giant disk galaxies predominant in many studies.
Identifying the Host Galaxies for Optically Dark Gamma-Ray Bursts
We propose to use the high spatial resolution of Chandra to obtain precise positions for a sample of Gamma-Ray Bursts (GRBs) with no optical afterglows, where the optical light is suppressed relative to the X-ray flux. These bursts are likely to be highly obscured and may have different environments from the optically bright GRBs. Our Chandra observations will (unlike Swift XRT positions) allow for the unique identification of a host galaxy. To locate these host galaxies we will follow up our Chandra positions with deep optical and IR observations with HST. The ultimate aim is to understand any differences between the host galaxies of optically dark and bright GRBs, and how these affect the use of GRBs as tracers of starformation and galaxy evolution at high redshift.
The First Proper Motion Measurement for M31: Dynamics and Mass of the Local Group
We will perform observations to determine the proper motion of the Andromeda galaxy M31, which has been sought for almost a century without success. While challenging, this measurement has now become possible due to the availability of existing deep ACS/WFC images of several M31 fields. The requested second epoch images will yield the average shift of the M31 stars with respect to compact galaxies in the background. Our observing strategy uses six different fields (three primary and three coordinated parallel) with two different instruments (ACS and WFC3) to provide a maximum handle on possible systematic effects. The expected result will be sufficiently accurate to: (a) discriminate between different histories for the dynamics of the Local Group; (b) constrain the mass distribution of the Local Group; (c) determine the details of the expected future merger between M31 and the Milky Way; (d) infer the past interaction history between M31 and M33; (e) constrain the internal proper motion kinematics of the M31 spheroid, outer disk, and tidal stream; and (f) obtain a pilot estimate of the M31 distance through the method of rotational parallax.
Formation and Evolution of Massive Galaxies in the Richest Environments at 1.5 < z < 2.0
We propose to image seven 1.5< z<2 clusters and groups from the IRAC Shallow Cluster Survey with WFC3 and ACS in order to study the formation and evolution of massive galaxies in the richest environments in the Universe in this important redshift range. We will measure the evolution of the sizes and morphologies of massive cluster galaxies, as a function of redshift, richness, radius and local density. In combination with allocated Keck spectroscopy, we will directly measure the dry merger fraction in these clusters, as well as the evolution of Brightest Cluster Galaxies (BCGs) over this redshift range where clear model predictions can be confronted. Finally we will measure both the epoch of formation of the stellar populations and the assembly history of that stellar mass, the two key parameters in the modern galaxy formation paradigm.
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).
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.
Orbits, Masses, Densities, and Colors of Two Transneptunian Binaries
Binaries are the key to learning many crucial bulk properties of transneptunian objects (TNOs) including their masses. Perhaps the most interesting mass-dependent property of a TNO is its bulk density, which provides unique information about its bulk composition and interior structure. Densities have so far only been measured for a handful of binary TNO systems. This proposal seeks to determine orbits and thus masses of two more binary TNOs, both of which are also to be observed at thermal infrared wavelengths by the Herschel spacecraft. Combining the masses from Hubble with the sizes from Herschel will enable us to compute their densities. We will also obtain multi-wavelength photometric colors of the individual components of each binary system. It is imperative to link colors to the physical properties measurable in binary systems in order to use the remnant planetesimals in today's Kuiper belt to learn more about the early history of our own solar system, and more generally about how planetesimals form in nebular disks and subsequently evolve.
A Search for Astrometric Companions to Very Low-Mass, Population II Stars
We propose to carry out a Snapshot search for astrometric companions in a subsample of very low-mass, halo subdwarfs identified within 120 parsecs of the Sun. These ultra-cool M subdwarfs are local representatives of the lowest-mass H burning objects from the Galactic Population II. The expected 3-4 astrometric doubles that will be discovered will be invaluable in that they will be the first systems from which gravitational masses of metal-poor stars at the bottom of the main sequence can be directly measured.
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).
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.