This week on HST

HST Programs: Septermber 5, 2011 - September 11, 2011

Program Number Principal Investigator Program Title
11670 Peter Garnavich, University of Notre Dame The Host Environments of Type Ia Supernovae in the SDSS Survey
12023 James C. Green, University of Colorado at Boulder COS-GTO: Cold ISM
12031 James C. Green, University of Colorado at Boulder COS-GTO: Sampling the Local ISM with hot white dwarfs - Part 2
12035 James C. Green, University of Colorado at Boulder COS-GTO: Activity of Solar Mass Stars from Cradle to Grave Part 2
12039 James C. Green, University of Colorado at Boulder COS-GTO: X-Ray Binaries
12099 Adam Riess, The Johns Hopkins University Supernova Follow-up for MCT
12102 Marc Postman, Space Telescope Science Institute Through a Lens, Darkly - New Constraints on the Fundamental Components of the Cosmos
12103 Marc Postman, Space Telescope Science Institute Through a Lens, Darkly - New Constraints on the Fundamental Components of the Cosmos
12106 Julianne Dalcanton, University of Washington A Panchromatic Hubble Andromeda Treasury - I
12169 Boris T. Gaensicke, The University of Warwick The frequency and chemical composition of planetary debris discs around young white dwarfs
12177 Pieter van Dokkum, Yale University 3D-HST: A Spectroscopic Galaxy Evolution Treasury
12185 Jenny E. Greene, University of Texas at Austin The Hosts of Megamaser Disk Galaxies
12188 Jay B. Holberg, University of Arizona Tests of Extreme Physics in Very Cool White Dwarfs
12190 Anton M. Koekemoer, Space Telescope Science Institute WFC3/IR Spectroscopy of the Highest Redshift Black Hole Candidates
12192 James T. Lauroesch, University of Louisville Research Foundation, Inc. A SNAPSHOT Survey of Interstellar Absorption Lines
12206 Mark S. Westmoquette, European Southern Observatory - Germany Starburst-driven shocks and feedback in the near-IR at high resolution
12239 Gilda E. Ballester, University of Arizona Springtime at Uranus: Upheaval in the Stratosphere?
12254 Adrienne Cool, San Francisco State University Helium-core White Dwarfs and Cataclysmic Variables in NGC 6752: New Clues to the Dynamical Evolution of Globular Clusters
12269 Claudia Scarlata, University of Minnesota - Twin Cities The escape of Lya photons in star-forming galaxies
12272 Christy A. Tremonti, University of Wisconsin - Madison Testing Feedback: Morphologies of Extreme Post-starburst Galaxies
12283 Matthew A. Malkan, University of California - Los Angeles WFC3 Infrared Spectroscopic Parallel Survey {WISP}: A Survey of Star Formation Across Cosmic Time
12298 Richard S. Ellis, California Institute of Technology Towards a Physical Understanding of the Diversity of Type Ia Supernovae
12307 Andrew J. Levan, The University of Warwick A public SNAPSHOT survey of gamma-ray burst host galaxies
12320 Brian Chaboyer, Dartmouth College The Ages of Globular Clusters and the Population II Distance Scale
12330 J. Davy Kirkpatrick, California Institute of Technology Spitzer Verification of the Coldest WISE?selected Brown Dwarfs
12514 Karl Stapelfeldt, NASA Goddard Space Flight Center Imaging of Newly-identified Edge-on Protoplanetary Disks in Nearby Star-Forming Regions
12549 Thomas M. Brown, Space Telescope Science Institute The Formation History of the Ultra-Faint Dwarf Galaxies
12576 Paul Kalas, University of California - Berkeley Orbit determination for Fomalhaut b and the origin of the debris belt halo
12686 Stephen Bradley Cenko, University of California - Berkeley Sw J2058+05: A Possible Second Relativistic Tidal Disruption Flare

Selected highlights

GO 11670: The Host Environments of Type Ia Supernovae in the SDSS Survey

SN 2007uy and 2008D in NGC 2770
Supernovae have long attracted the attention of both amateur and professional astronomers as a means of studying the violent eruption and death of massive stars and degenerates. However, in the last decade they have also acquired considerable importance as distance indicators, tracing the expansion of the universe to redshifts well beyond the reach of more conventional yardsticks, such as cepheids, and providing a key underpinning for the hypothesised existcen of dark energy. Understanding the supernovae themselves, and, in particular, their progenitors, is key to accurately interpreting their luminosities and distances. The present program aims to tackle that aspect of the problem by using ACS to obtain deep, high resolution images of galaxies that have harboured recent type Ia supernovae. The targets are all drawn from the Sloan Digital Sky Survey, which has uncovered more than than 500 type Ia supernovae,. The supernovae themselves are long gone from view, but the ACS data will be used to probe the stellar populations in the immediate vicinity of the explosion, and hence gain a better understanding of the likely progenitor.

GO 12102: Through a Lens, Darkly - New Constraints on the Fundamental Components of the Cosmos

The ACS optical/far-red image of the galaxy cluster, Abell 2218, including an extensive number of lensed arcs
The overwhelming majority of galaxies in the universe are found in clusters. As such, these systems offer an important means of tracing the development of large-scale structure through the history of the universe. Moreover, as intense concentrations of mass, galaxy clusters provide highly efficient gravitational lenses, capable of concentrating and magnifying light from background high redshift galaxies to allow detailed spectropic investigations of star formation in the early universe. Hubble imaging has already revealed lensed arcs and detailed sub-structure within a handful of rich clusters. At the same time, the lensing characteristics provide information on the mass distribution within the lensing cluster. The present program aims to capitalise fully on HST's imaging capabilities, utilising the refurbished Advanced Camera for Surveys and the newly-installed Wide-Field Camera 3 to obtain 17-colour imaging of 25 rich clusters. The data will be use to map the mass profiles of the clusters and probe the characteristics of the high-redshift lensed galaxies. Since ACS and WFC3 can be operated in parallel, the program will also use parallel imaging in offset fields to search for high-redshift supernovae. The present observations target the cluster MACS 2137-2353.

GO 12320: The Ages of Globular Clusters and the Population II Distance Scale

Hubble Heritage image of the globular cluster, M15
Globular clusters are the oldest structures within the Milky Way that are directly accessible to observation. They are relatively simple systems, with relatively simple colour-magnitude diagrams (albeit with some complexities adduced from recent HST observations, see GO 11233 ). Matching those CMDs against theoretical models allows us to set constraints on the age of the oldest stars in the Galaxy, and hence on the age of the Milky Way and the epoch of galaxy formation. However, the accuracy of those age determinations rest crucially on the accuracy of the cluster distance determinations. The clusters themselves lie at distances of several kpc at best, and tens of kpc at worst; thus, direct trigonometric parallax measurements must await microacrsecond astrometric missions. The classical method of deriving distances is main sequence fitting - using nearby stars, with similar chemical abundances and accurate parallax measurements, to map out the main sequence in absolute units, and then scaling the cluster data to fit. The problem with this method is that metal-poor subdwarfs are rare, so even Hipparcos was only able to obtain accurate distances to a handful of stars. The present program aims to improve the distance measurements by using the Fine Guidance Sensors on HST to determine sub-millarcsecond trigonometric parallaxes to 9 subdwarfs, almost doubling the sample available for MS fitting.

GO 12330: Spitzer Verification of the Coldest WISE-selected Brown Dwarfs

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 M<\sub>Jup, 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 recently completed its all-sky survey. WISE has succeeded in identifying a number of extremely interesting sources, including at least 4 objects that have been confirmed as dwarfs with temperatures lower than 350K. These are among the first examples of Y dwarfs. The current program is combining WFC3-grism imaging with warm-Spitzer photometry to verify the nature of further candidates.

Past weeks:
page by Neill Reid, updated 2/5/2011