This week on HST


HST Programs: July 9 - July 15, 2007

Program Number Principal Investigator Program Title Links
10806 Danny Steeghs, Smithsonian Institution Astrophysical Observatory Accretion in the closest binary systems known Abstract
10810 Edwin Anthony Bergin, University of Michigan The Gas Dissipation Timescale: Constraining Models of Planet Formation Abstract
10818 Judith Cohen, California Institute of Technology Very Young Globular Clusters in M31 ? Abstract
10872 Harry Teplitz, California Institute of Technology Lyman Continuum Emission in Galaxies at z=1.2 Abstract
10874 Wei Zheng, The Johns Hopkins University Search for Extremely Faint z>7 Galaxy Population with Cosmic Lenses Abstract
10884 Gray Wegner, Dartmouth College The Dynamical Structure of Ellipticals in the Coma and Abell 262 Clusters Abstract
10893 Peter Garnavich, University of Notre Dame Sweeping Away the Dust: Reliable Dark Energy with an Infrared Hubble Diagram Abstract
10902 Goran Ostlin, Stockholm University The Nearest Luminous Blue Compact Galaxies: A Window on Galaxy Formation Abstract
10904 David Thilker, The Johns Hopkins University Star formation in extended UV disk (XUV-disk) galaxies Abstract
10920 Tim Heckman, The Johns Hopkins University High-Resolution Imaging of Nearby Lyman Break Galaxy Analogs in the GALEX All-Sky Survey Abstract
10924 Alice Shapley, Princeton University Constraints on the Assembly and Dynamical Masses of z~2 Galaxies Abstract
11079 Luciana Bianchi, The Johns Hopkins University Treasury Imaging of Star Forming Regions in the Local Group: Complementing the GALEX and NOAO Surveys Abstract
11080 Daniela Calzetti, University of Massachusetts Exploring the Scaling Laws of Star Formation Abstract
11113 Keith S. Noll, Space Telescope Science Institute Binaries in the Kuiper Belt: Probes of Solar System Formation and Evolution Abstract
11157 Joseph H. Rhee, University of California - Los Angeles NICMOS Imaging Survey of Dusty Debris Around Nearby Stars Across the Stellar Mass Spectrum Abstract
11175 Sandra M. Faber, University of California - Santa Cruz UV Imaging to Determine the Location of Residual Star Formation in Galaxies Recently Arrived on the Red Sequence Abstract
11178 William M. Grundy, Lowell Observatory Probing Solar System History with Orbits, Masses, and Colors of Transneptunian Binaries Abstract
11210 George Fritz Benedict, University of Texas at Austin The Architecture of Exoplanetary Systems Abstract
11211 George Fritz Benedict, University of Texas at Austin An Astrometric Calibration of Population II Distance Indicators Abstract
11212 Douglas R. Gies, Georgia State University Research Foundation Filling the Period Gap for Massive Binaries Abstract
11214 John Wisniewski, NASA Goddard Space Flight Center HST/FGS Astrometric Search for Young Planets Around Beta Pic and AU Mic Abstract
11218 Howard Bond, Space Telescope Science Institute Snapshot Survey for Planetary Nebulae in Globular Clusters of the Local Group Abstract
11229 Margaret Meixner, Space Telescope Science Institute SEEDS: The Search for Evolution of Emission from Dust in Supernovae with HST and Spitzer Abstract
11289 Jean-Paul Kneib, Laboratoire d'Astronomie Spatiale SL2S: The Strong Lensing Legacy Survey Abstract

Some selected highlights

GO 10810: The Gas Dissipation Timescale: Constraining Models of Planet Formation

Hubble ACS image of the face-on debris disk around the nearby G dwarf, HD 107146 While much debate has raged in recent months over exactly how to define a planet, there is very little debate in the astronomical community about where planets form: they form in circumstellar disks. During the earliest stages of their existence, the disks are dusty, gas-rich and high opacity; for example, see NICMOS images of T Tauri stars and IRAS sources and current HST proposals 10540 and 10864. After only ~10 million years, however, most of the gas dissipates, leaving a young planetary system with a rich content of dust, rocks, planetoids and planets. This period corresponds to the high bombardment phase in earth's history, when the Moon was formed. To the outside observer, the dusty disk has low surface brightness, and is much less prominent than the gaseous disk. HST can image these disks via scattered light at near-infrared and, in a few cases, optical wavelengths - probably the most spectacular example is Beta Pic (see the recent HST ACS images ). Recent models suggest that, while these debris disks have a much lower gaseous content than classic T Tauri disks, they should retain some gas content, which can be crucial in influencing planet formation. The aim of the present program is to use the prism on the UV-sensitive ACS Solar Blind Channel SBC) to search for molecular hydrogen absorption at 1600 Angstroms. The program targets 11 systems with ages between 10 and 50 Myrs, including two members of the TW Hydrae association.

GO 10920: High-Resolution Imaging of Nearby Lyman Break Galaxy Analogs in the GALEX All-Sky Survey

Mosaic of HST images of M82, the best-known starburst galaxy Current Big Bang cosmological models predict that the universe should have undergone a global re-ionisation at redshifts between 6 and 20. The first generation of stars is generally tapped as the most likely source of the ionising radiation, perhaps enhanced through merger-stimulated starbursts. Direct observations of those galaxies are not possible at present; the James Webb Space Telescope is expected to open up observations of these systems. In consequence, there is considerable interest in identifying galaxies at lower redshifts that could serve as analogues for the z>6 systems. over the last few years, the Galaxy Evolution Explorer (GALEX) has proved an important new tool in identifying candidate objects. GALEX has conducted an all-sky survey at ultraviolet wavelengths, and has uncovered sigificant numbers of UV luminous galaxies at low and moderate redshifts. Many of these galaxies are starbursts, undergoing substantial outbursts of star formation. The present program was designed to use ACS to image a subset'of those galaxies at optical and near-UV wavelengths. With the demise of the ACS?WFC and ACS/HRC, WFPC2 is currently being used to complete the program.

GO 11080: Exploring the Scaling Laws of Star Formation

UKST R-band image of the interacting pair, NGC 833 and NGC 835 Understanding the star formation process is crucial to our developing viable theories of galaxy formation. The present program aims to investigate this process by obtaining NICMOS Paschen-alpha images of the central regions of an all-sky sample 84 nearby spiral and S0 galaxies. The near-infrared images will be combined with CO and HI interferometric radio maps, and, where such data are available, mid-infrared imaging by Spitzer, probing the relative distributions of gas, dust and star formation in these galaxies. Besides studying how the star formation rate (SFR) varies as a function of gas density, the NICMOS data will permit high spatial-resolution investigations of where (and whether) Schmidt-type star-formation "laws" (power-law relations between the SFR and gas density) are valid in external galaxies. This week's observations target NGC 833 and NGC 835, an interacting pair of spirals in the compact group, Hickson 16.

GO 11178: Probing Solar System History with Orbits, Masses, and Colors of Transneptunian Binaries

Preliminary orbital determination for the KBO WW31, based on C. Veillet's analysis of CFHT observations; the linked image shows the improved orbital derivation, following the addition of HST imaging The Kuiper Belt consists of icy planetoids that orbit the Sun within a broad band stretching from Neptune's orbit (~30 AU) to distance sof ~50 AU from the Sun (see David Jewitt's Kuiper Belt page for details). Over 500 KBOs (or trans-Neptunian objects, TNOs) are currently known out of a population of perhaps 70,000 objects with diameters exceeding 100 km. Approximately 2% of the known KBOs are binary (including Pluto, one of the largest known KBOs, regardless of whether one considers it a planet or not). This is a surprisingly high fraction, given the difficulties involved in forming such systems and the relative ease with which they can be disrupted. It remains unclear whether these systems formed from single KBOs (through collisions or 3-body interactions) as the Kuiper Belt and the Solar System have evolved, or whether they represent the final tail of an initial (much larger) population of primordial binaries. These issues can be addressed, at least in part, through deriving a better understanding of the composition of KBOs - and those properties can be deduced by measuring the orbital parameters for binary systems. The present proposal will use the Planetary camera on WFPC2 to determine the relative orbits for several known KBO binaries. Just as with binary stars, the orbital period and semi-major axis give the total system mass, while the mid-infrared properties (measured by Spitzer) allow an assessment of the surface area/diameters; combining these measurements gives an estimate of the mean density.

Past weeks:
page by Neill Reid, updated 29/6/2007