This week on HST

HST Programs: April 11, 2011 - April 17, 2011

Program Number Principal Investigator Program Title
11616 Gregory J. Herczeg, Max-Planck-Institut fur extraterrestrische Physik The Disks, Accretion, and Outflows {DAO} of T Tau stars
12024 James C. Green, University of Colorado at Boulder COS-GTO: Great Wall Tomography - Part 2
12066 Marc Postman, Space Telescope Science Institute Through a Lens, Darkly - New Constraints on the Fundamental Components of the Cosmos
12163 Aaron J. Barth, University of California - Irvine Structure and Stellar Content of the Nearest Nuclear Clusters in Late-Type Spiral Galaxies
12167 Marijn Franx, Universiteit Leiden Resolving the Matter of Massive Quiescent Galaxies at z=1.5-2
12169 Boris T. Gaensicke, The University of Warwick The frequency and chemical composition of planetary debris discs around young white dwarfs
12184 Xiaohui Fan, University of Arizona A SNAP Survey for Gravitational Lenses Among z~6 Quasars
12192 James T. Lauroesch, University of Louisville Research Foundation, Inc. A SNAPSHOT Survey of Interstellar Absorption Lines
12194 Mattia Negrello, Open University High resolution Near-Infrared imaging of the first sub-mm selected gravitational lens candidates in the Herschel ATLAS
12195 Masamune Oguri, National Astronomical Observatory of Japan (NAOJ) Understanding the Largest Quasar Lens SDSS J1029+2623
12210 Adam S. Bolton, University of Utah SLACS for the Masses: Extending Strong Lensing to Lower Masses and Smaller Radii
12212 D. Michael Crenshaw, Georgia State University Research Foundation What are the Locations and Kinematics of Mass Outflows in AGN?
12219 Antonino Milone, Instituto de Astrofisica de Canarias Multiple stellar generations in the Large Magellanic Cloud Star Cluster NGC 1846
12220 Rupal Mittal, Rochester Institute of Technology Linking Star Formation with Intracluster Medium Cooling and AGN Heating in a Sample of Herchel Galaxy Clusters
12230 Mark Raboin Swain, Jet Propulsion Laboratory The effect of radiation forcing on an exoplanet atmosphere
12248 Jason Tumlinson, Space Telescope Science Institute How Dwarf Galaxies Got That Way: Mapping Multiphase Gaseous Halos and Galactic Winds Below L*
12250 John Bally, University of Colorado at Boulder Irradiated Jets and Proplyds in NGC 1977, Orion Nebula's Cousin
12272 Christy A. Tremonti, University of Wisconsin - Madison Testing Feedback: Morphologies of Extreme Post-starburst Galaxies
12275 Bart P. Wakker, University of Wisconsin - Madison Measuring gas flow rates in the Milky Way
12286 Hao-Jing Yan, The Ohio State University Hubble Infrared Pure Parallel Imaging Extragalactic Survey {HIPPIES}
12287 Scott D. Friedman, Space Telescope Science Institute Constraining Models of Deuterium Depletion and Galactic Chemical Evolution with Improved Measurements of D/H
12315 Hans Moritz Guenther, Smithsonian Institution Astrophysical Observatory Winds, accretion and activity: Deciphering the FUV lines in TW Hya
12322 Kailash Sahu, Space Telescope Science Institute Detecting Isolated Black Holes through Astrometric Microlensing
12324 C. S. Kochanek, The Ohio State University The Temperature Profiles of Quasar Accretion Disks
12328 Pieter van Dokkum, Yale University 3D-HST: A Spectroscopic Galaxy Evolution Treasury Part 2
12368 Roger G. Morris, Stanford University Extreme Mergers from the Massive Cluster Survey

Selected highlights

GO 11616: The Disks, Accretion, and Outflows (DAO) of T Tau stars

Wide-field image, from NOAO, of T Tauri and its immediate environs The T Tauri stage of evolution occurs early in a star's lifetime, within ~10 Myrs of its birth, when it still retains a dense, dust and gas-rich circumstellar disk. During this phase, there is substantial accretion of material onto the central star. This leads to heating of the inner regions of the accretion disk, and significant emission at ultraviolet and X-ray wavelengths. Previous HST programs (e.g. GO 10840 ) have used the STIS and the ACS/SBC to investigate these processes at FUV wavelengths. The present program will extend those investigations using COS, which provides more than an order of magnitude more sensitivity and resolution. The survey will target 32 T Tauri stars, including 26 "classical" T Tauris and 6 "weak-lined" T Tauris (the latter are surrounded by less disk material, and are generally believed to be at a later stage of evolution than the CTTs). COS will be used to measure the emission profiles of an extensive number of lines, probing opacities, temperatures and densities in the disk and outflow regions.

GO 12195: Understanding the Largest Quasar Lens SDSS J1029+2623

Gravitational lensing is a consequence of general relativity. Its importance as an astrophysical tool first became apparent with the realisation (in 1979) that the quasar pair Q0957+561 actually comprised two lensed images of the same background quasar. In the succeeding years, lensing has been used primarily to probe the mass distribution of galaxy clusters, using theoretical models to analyse the arcs and arclets that are produced by strong lensing of background galaxies, and the large-scale mass distribution, through analysis of weak lensing effects on galaxy morphologies. Gravitational lensing also increases the apparent brightness of the background sources. This effect can be used to our advantage, in enabling detailed observations of high-redshift sources that be too faint to observe under normal circumstances, but it can also lead to statistical biases in parameters such as luminosity functions. These effects are likely to be of most importance for higher redshift sources, where the longer pathlength leads to a higher probability of the light encountering a foreground lens. The present program focuses on SDSS J1029+2623, a z=2.197 quasar that is being lensed by a z=0.60 galaxy cluster. The lensed system comprises three images, including two with a separation of 22.5 arcseconds, the largest separation currently known for any lensed quasar. The present program aims to use WFC3 and ACS to search for other examples of multiply-imaged background galaxies, to further constrain the cluster potential.

GO 12219: Multiple stellar generations in the Large Magellanic Cloud Star Cluster NGC 1846

The colour-magnitude diagram from the LMC cluster, NGC 1846 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. Omega Cen has been joined by several additional 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. The present program aims extend coverage to clusters in the LMC, which also show some evidence for this behaviour. NGC 1846, one of the brighter clusters, will be targeted with WFC3, both UVIS and NIR, and ACS.

GO 12275: Measuring gas flow rates in the Milky Way

A map of the high velocity cloud systems surrounding the Milky Way (B. Wakker, U. Wisconsin). The stellar components of the Milky Way Galaxy are well known: the disk, the central bulge and the old, metal-poor stellar halo. However, the Milky Way is also surrounded by a halo of hot, gas that is itself embedded within a much more tenuous corona of even hotter, ionised gas. Within that structure lie high velocity clouds. Originally discovered in the 1930s as absorption features in stellar spectra, these clouds have velocities that differ significantly from the rotational velocity along that line of sight, and they are generally believed to be undergoing infall into the Galaxy. The origin and nature of these systems remains uncertain, with some favouring a Galactic origin, driven by star formation and feedback between disk and halo, and others supporting their origin within the warm-hot intergalactic medium. HVCs are not self luminous, so indirect methods need to be applied to examine their characteristics. The most effective is to identify stars that lie behind individual systems and, as with their discovery in the 1930s, search the stellar spectra for signature absorption lines produced by material within the cloud. Many, indeed most, of the key absorption features lie at ultraviolet wavelengths, a spectral region that has been opened up with the installation of the Cosmic Origins Spectrograph on HST. Detailed information is currently available for only five HVCs. The present program is using active galactic nuclei (AGNs) as background light sources to probe most of the remaining known HVCs within the Milky Way.

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