This week on HST


HST Programs: April 4 - April 10, 2016

Program Number Principal Investigator Program Title
13646 Ryan Foley, University of Illinois at Urbana - Champaign Understanding the Progenitor Systems, Explosion Mechanisms, and Cosmological Utility of Type Ia Supernovae
13750 John M. Cannon, Macalester College Fundamental Parameters of the SHIELD II Galaxies
14069 Nate Bastian, Liverpool John Moores University Searching For Multiple Populations in Massive Young and Intermediate Age Clusters
14073 Martha L. Boyer, University of Maryland Assessing the Impact of Metallicity on Stellar Dust Production
14076 Boris T. Gaensicke, The University of Warwick An HST legacy ultraviolet spectroscopic survey of the 13pc white dwarf sample
14094 Vincent Bourrier, Observatoire de Geneve Characterization of the extended atmosphere and the nature of the hot super-Earth 55 Cnc e and the warm Jupiter 55 Cnc b
14096 Dan Coe, Space Telescope Science Institute - ESA RELICS: Reionization Lensing Cluster Survey
14103 Jian-Yang Li, Planetary Science Institute Born Small or Gone Small - Determining the Evolutionary State of Comet 252P/LINEAR during its Close Approach to Earth
14119 Luciana C. Bianchi, The Johns Hopkins University Understanding Stellar Evolution of Intermediate-Mass Stars from a New Sample of SiriusB-Like Binaries
14127 Michele Fumagalli, Durham Univ. First Measurement of the Small Scale Structure of Circumgalactic Gas via Grism Spectra of Close Quasar Pairs
14134 Swara Ravindranath, Space Telescope Science Institute Spectral Diagnostics for the Reionization Era: Exploring the Semi-Forbidden CIII] Emission in Low Metallicity Green Pea Galaxies
14137 Lorrie Straka, Sterrewacht Leiden Damped Lyman-alpha Systems in the Disks of Low-z SDSS Galaxies on Top of QSOs
14139 Lifan Wang, Texas A & M University Imaging Polarimetry of Light Echoes around SN 2014J
14157 Kevin Luhman, The Pennsylvania State University Testing Model Atmospheres with the Coldest Known Brown Dwarf
14168 Daniel P. Stark, University of Arizona COS Views of He II Emitting Star Forming Galaxies: Preparing for the JWST Era
14171 Guangtun Zhu, The Johns Hopkins University Characterizing the Circumgalactic Medium of Luminous Red Galaxies
14178 Matthew A. Malkan, University of California - Los Angeles WFC3 Infrared Spectroscopic Parallel Survey: The WISP Deep Fields
14216 Robert P. Kirshner, Harvard University RAISIN2: Tracers of cosmic expansion with SN IA in the IR
14219 John P. Blakeslee, Dominion Astrophysical Observatory Homogeneous Distances and Central Profiles for MASSIVE Survey Galaxies with Supermassive Black Holes
14222 David Ehrenreich, Observatoire de Geneve Full HST coverage of a comet-like exoplanet in transit
14227 Casey Papovich, Texas A & M University The CANDELS Lyman-alpha Emission At Reionization (CLEAR) Experiment
14241 Daniel Apai, University of Arizona Cloud Atlas: Vertical Cloud Structure and Gravity in Exoplanet and Brown Dwarf Atmospheres
14246 Douglas R. Gies, Georgia State University Research Foundation The Fastest Rotating Stars
14251 Amy E. Reines, National Optical Astronomy Observatory, AURA The Structures of Dwarf Galaxies Hosting Massive Black Holes
14265 Tae-Sun Kim, INAF, Osservatorio Astronomico di Trieste Crossing the redshift desert: ionizing background radiation and intergalactic hydrogen at z ~ 1
14269 Nicolas Lehner, University of Notre Dame Just the BASICs: Linking Gas Flows in the Circumgalactic Medium to Galaxies
14327 Saul Perlmutter, University of California - Berkeley See Change: Testing time-varying dark energy with z>1 supernovae and their massive cluster hosts
14356 Richard M. Plotkin, International Centre for Radio Astronomy Research - Curtin Multiwavelength Characterization of Candidate Black Holes in Nearby Dwarf Galaxies
14453 Diana Dragomir, University of Chicago The Nature of 55 Cancri e

Selected highlights

GO 14069: Searching For Multiple Populations in Massive Young and Intermediate Age Clusters


HST image of the LMC cluster, NGC 1866
Globular clusters are remnants of the first substantial burst of star formation in the Milky Way. With typical masses of a few x 105 solar masses, distributed among several x 106 stars, the standard picture holds that these are simple systems, where all the stars formed in a single starburst and, as a consequence, have the same age and metallicity. Until recently, the only known exception to this rule was the cluster Omega Centauri, which is significantly more massive than most clusters and has both double main sequence and a range of metallicities among the evolved stars. Over the past 5-10 years, Omega Cen has been joined by numerous other Galactic clusters, including NGC 2808, which shows evidence for three distinct branches to the main sequence, NGC 1851, 47 Tucanae and NGC 6752 - all relatively massive clusters. In almost all cases, the complexity of these systems has only emerged through the high precision observations possible with HST. Hubble is now being turned towards clusters in our nearest neighbour galaxies, the Large and Small Magellanic Clouds. Previousl observations have obtained of the massive cluster NGC 1846. The present program aims to extends coverage to a dozen other clusters, including NGC 419, 1783, 1850 and 1866. The clusters span a wide range of ages, from ~100 Myrs to close to 10 Gyrs. The WFC3-UVIS camera will be used to obtain UV (F343N, F336W) and blue-band (F438W) images to search for evidence of multiple populations in the colour-magnitude diagrams.

GO 14157: Testing Model Atmospheres with the Coldest Known Brown Dwarf


The stellar menagerie: Sun to Jupiter, via brown dwarfs
Brown dwarfs are objects that form in the same manner as stars, by gravitational collapse within molecular clouds, but which do not accrete sufficient mass to raise the central temperature above ~2 million Kelvin and ignite hydrogen fusion. As a result, these objects, which have masses less than 0.075 MSun or ~75 MJup, lack a sustained source of energy, and they fade and cool on relatively short astronomical (albeit, long anthropological) timescales. Following their discovery over a decade ago, considerable observational and theoretical attention has focused on the evolution of their intrinsic properties, particularly the details of the atmospheric changes. At their formation, most brown dwarfs have temperatures of ~3,000 to 3,500K, comparable with early-type M dwarfs, but they rapidly cool, with the rate of cooling increasing with decreasing mass. As temperatures drop below ~2,000K, dust condenses within the atmosphere, molecular bands of titanium oxide and vanadium oxide disappear from the spectrum to be replaced by metal hydrides, and the objects are characterised as spectral type L. Below 1,300K, strong methane bands appear in the near-infrared, characteristics of spectral type T. At present, the coolest T dwarfs known have temperatures of ~650 to 700K. At lower temperatures, other species, notably ammonia, are expected to become prominent, and a number of efforts have been undertaken recently to find examples of these "Y" dwarfs. The search is complicated by the fact that such objects are extremely faint instrinsically, so only the nearest will be detectable. Identifying such ultra-ultracool dwarfs was a goal of the WISE satellite mission, which completed an all-sky survey in 2011 (and is currently being employed in a search for Near-Earth Objects, NEOWISE). WISE has identified several Y dwarfs, including several with temperatures lower than 350K. The most interesting source was discovered by Kevin Luhman (Penn State), WISE0855-071, a brown dwarf lying only 2.2 parsecs from the Sun with a surface temperature around 250 K. The object is extremelty faint and is detectable only by virtue of its proximity. Previously, Hubble obtained J-band imaging with the F110W filter on WFC3-IR; the present program aims add detections in the far red (F850LP) with ACS and near-infrared (F105W and F127M) with WFC3-IR.

GO 14171: Characterizing the Circumgalactic Medium of Luminous Red Galaxies


A computer simulation of galactic gas accretion and outflow
Galaxy formation, and the overall history of star formation within a galaxy, clearly demands the presence of gas. The detailed evolution therefore is tied very closely to how gas is accreted, recycled, circulated through the halo and disk, and, perhaps, ejected back into the intergalactic medium. Tracing that evolutionary history is difficult, since gas passes through many different phases, some of which are easier to detect than others. During accretion and, probably, subsequent recycling, the gas is expected to be reside predominantly at high temperatures. The most effective means of detecting such gas is through ultraviolet spectroscopy, where gas within nearby systems can be detected as absorption lines superimposed on the spectra of more distant objects, usually quasars. The present program is using the Cosmic Origins Spectrograph to probe gas in the circumgalactic medium for a large sample of luminous red galaxies at redshifts z~0.5. The targets are drawn from the SDSS-III/Baryon Oscillation Spectroscopic Survey (BOSS). All of these systems have background quasars lying at small angular separations, corresponding to linear separatiosn of ~100 kpc at distance of the target galaxies. Ground-based observations of those quasars indicate the rpesent of ionised magnesium (MgII) absorption due to halo gas associated with the foreground galaxy. COS will be used to probe the presence of hydrogen, through lyman alpha absorption, as well as more highly ionised elements, such as C III, Si III and P VI.

GO 14227: The CANDELS Lyman-alpha Emission At Reionization (CLEAR) Experiment


Part of the GOODS/Chandra Deep Field South field, as imaged by HST
Hubble has made significant contributions in many science areas, but galaxy formation, assembly and evolution is a topic that has been transformed by the series of deep fields obtained over the past 20 years. CANDELS, one of three Multi-Cycle Treasury Program executed in cycles 18 through 20, is one of the more recent additions to this genre.Building on past investment of both space- and ground-based observational resources, it covers five five fields including both the Great Observatory Origins Deep Survey (GOODS), centred on the northern Hubble Deep Field (HDF) in Ursa Major and the Chandra Deep Field-South in Fornax. In addition to deep HST data at optical and near-infrared wavelengths, the fields have been covered at X-ray wavelengths by Chandra (obviously) and XMM-Newton; at mid-infrared wavelengths with Spitzer; and ground-based imaging and spectroscopy using numerous telescopes, including the Kecks, Surbaru and the ESO VLT. This represents an accumulation of almost 1,000 orbits of HST time, and comparable scale allocations on Chandra, Spitzer and ground-based facilities. CANDELS added new optical and near-infrared observations with WFC3 and ACS (see this link for more details). Those data have been processed and analysed by both the CANDELS team and by other groups within the community. The present program builds on this foundation by adding 16 pointings within the CANDELS fields with the WFC3 G102 grism. The goal is to probe reionisation by measuring the strength of Lyman-alpha absorption in galaxies at redshifts between z=6.5 and z=8.2. The expectation is that the ovall absorption strength should decrease with decreasing redshift as the intergalactic medium is ionised, and the proportion of neutral gas decreases.

Past weeks:
page by Neill Reid, updated 23/12/2014
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