This week on HST

HST Programs: May 15 - May 21, 2006

Program Number Principal Investigator Program Title Links
10487 David Ardila, California Institute of Technology A Search for Debris Disks in the Coeval Beta Pictoris Moving Group Abstract
10496 Saul Perlmutter, Lawrence Berkeley National Laboratory Decelerating and Dustfree: Efficient Dark Energy Studies with Supernovae and Clusters Abstract
10503 Gary Da Costa, Australian National University The Star Formation Histories of Early Type Dwarf Galaxies in Low Density Environments: Clues from the Sculptor Group Abstract
10504 Richard Ellis, California Institute of Technology Characterizing the Sources Responsible for Cosmic Reionization Abstract
10512 William Merline, Southwest Research Institute Search for Binaries Among Faint Jupiter Trojan Asteroids Abstract
10519 Janet Simpson, NASA Ames Research Center Testing the Stellar Coalescence and Accretion Disk Theories of Massive Star Formation with NICMOS Abstract
10523 Roelof de Jong, Space Telescope Science Institute The Halo Shape and Metallicity of Massive Spiral Galaxies Abstract
10525 Suzanne Hawley, University of Washington Characterizing the Near-UV Environment of M Dwarfs: Implications for Extrasolar Planetary Searches and Astrobiology Abstract
10532 Kai Noeske, University of California - Santa Cruz Kinematics and morphology of the most massive field disk galaxies at z>1 Abstract
10533 Joana Oliveira, University of Keele The IMF in NGC6611: the environmental influence on the formation of low-mass stars and brown dwarfs Abstract
10536 Raghvendra Sahai, Jet Propulsion Laboratory What Are Stalled Preplanetary Nebulae? An ACS SNAPshot Survey Abstract
10544 David Bennett, University of Notre Dame Resolved Images of LMC Microlensing Events Observed by a Telescope at 2 AU from Earth Abstract
10551 Shri Kulkarni, California Institute of Technology Gamma-Ray Bursts from Start to Finish: A Legacy Approach Abstract
10554 Ray Sharples, University of Durham Globular Cluster Systems of Elliptical Galaxies in Low Density Environments Abstract
10556 David Turnshek, University of Pittsburgh Neutral Gas at Redshift z=0.5 Abstract
10559 Herve Bouy, Instituto de Astrofisica de Canarias Astrometric monitoring of binary L and T dwarfs Abstract
10587 Adam Bolton, Smithsonian Institution Astrophysical Observatory Measuring the Mass Dependence of Early-Type Galaxy Structure Abstract
10596 Luis Ho, Carnegie Institution of Washington AGNs with Intermediate-mass Black Holes: A Test of the Black Hole-Bulge Paradigm Abstract
10603 Deborah Padgett, California Institute of Technology Multiwavelength Imaging of Edge-on Protoplanetary Disks: Quantifying the Growth of Circumstellar Dust Abstract
10612 Douglas Gies, Georgia State University Research Foundation Binary Stars in Cyg OB2: Relics of Massive Star Formation in a Super-Star Cluster Abstract
10624 Derek B. Fox, California Institute of Technology Solving the Mystery of the Short-Hard Gamma-Ray Bursts Abstract
10626 Yeong-Shang Loh, University of Colorado at Boulder A Snapshot Survey of Brightest Cluster Galaxies and Strong Lensing to z = 0.9 Abstract
10635 Bodo Ziegler, Georg-August-Universitat Galaxy Transformation as probed by Morphology and Velocity Fields of Distant Cluster Galaxies Abstract
10767 Thomas Ayres, Univresity of Colorado at Boulder Further Resolving the Puzzle of Hybrid Star X-rays Abstract
10775 Ata Sarajedini, University of Florida An ACS Survey of Galactic Globular Clusters Abstract
10991 Arlin Crotts, Columbia University Light Echoes from SN 2006X in M100 Abstract

Some selected highlights

GO 10503: The star formation histories of early type dwarf galaxies in low density environments: Clues from the Sculptor Group

NGC 625 - a dwarf galaxy in the Sculptor group The Sculptor group is a relatively low density aggregate of 12-15 galaxies lying at a distance of approximately 3 Mpc. The dominant member is the spiral galaxy, NGC 253, and the group includes a handful of other relatively low luminosity spiral galaxies, but most members are dwarf irregular or elliptical galaxies. Recent observations have detected HI gas and, perhaps, limited numbers of hot, blue stars, suggesting modest star formation, in several dwarf systems - including systems classed as dE. This suggests that these might be "transition" dwarfs, similar to the nearby Phoenix dwarf and LGS3. This program is using the wide-field camera on ACS to obtain deep F606W and F814W images of five Sculptor dwarfs. The aim is to use the resultant colour-magnitude diagrams, which will encompass the upper reaches of the red giant branch and should reach below the horizontal branch in the nearer dwarfs, to study the star formation history in these relatively isolated systems.

GO 10523: The halo shape and metallicity of massive spiral galaxies

NGC 3031 ( M81 ) The subdwarf stars that populate the Galactic halo are generally recognised as fossil remnants of the first episode of substantial star formation to afflict the Milky Way galaxy. The structure and density distribution of our own halo has been inferred partly from deep starcounts, partly from globular cluster systems and partly from the kinematics of local subdwarfs; most analyses favour a near-spherical system with density r-3.5. The aim of this proposal is to extend these studies to seven other nearby spiral systems. ACS is being used to obtain WFC observations in the F550W and F814W filters at a series of locations along the major and minor axes, and along an intermediate-angle axis. A comparison of the colour-magnitude diagrams at different radial distances should permit separation of the contributions from disk, thick disk and bulge, and isolation of the halo population in those systems. The observations should allow measurement of the halo metallicity distribution and an estimate of the shape of the halo in these dwarf systems.

GO 10624: Solving the mystery of short-hard gamma-ray bursts

An artist's impression of a gamma-ray burst Gamma ray bursts are events that tap extraordinary energies (1045 to 1047 joules) in remarkably short periods of time. Several thousands bursts have been detected over the last 30+ years, and analyses indicate that they can be divided into two classes with durations longer or shorter than 2 seconds. The short bursts appear to release more high energy radiation, so the two subsets are known as long/soft and short/hard bursts. The long/soft bursts appear to originate in the collapse of very massive stars, while the short/hard bursts are coalescing binary systems (probably pairs of neutron stars or black holes). The first optical counterpart to a gamma ray burst was identified in 1998, allowing confirmation of their extragalactic nature, and, since then, more than 50 bursts have been detected at X-ray wavelengths, and half that number detected at either optical or radio wavelengths; all of these detections are long/soft bursts. The aim of this program is to focus on the short/hard bursters. This is a Target of Opportunity project, triggered by the detection of a suitable candidate by the Swift satellite, followed by the rapid (< 3 days detection of an optical afterglow. The aim is to obtain ACS observations (weither WFC or HRC) within 5-6 days of the burst, and use the resultant images to characterise the underlying host galaxy.

GO 10603: Multiwavelength imaging of edge-on protoplanetary disks: quantifying the growth of circumstellar dust

Schematic structure of an edge-on protoplanetary disk Circumstellar disks are the sites of planet formation. Forming due to angular momentum conservation as protostellar cores collapse to form protostars, disks are readily detectable around most stars younger than ~5 million years. During their youth, the disks have a high gas and dust content, which gradually disperses to leave residual debris disks around stars older than 10-20 million years. The present HST program focuses on several edge-on disk systems which are sufficiently opaque that the central star is obscured. Consequently, fine vertical structure in the disk becomes visible through reflected and scattered light. The aim of this program is to use both ACS and NICMOS to obtain multicolour imaging of these systems, and trace the wavelength dependence of scattering as a function of position in the disk. These observations can constrain grain size, and, to some extent, grain composition, and hence test models of grain growth in circumstellar disks.

Past weeks:
page by Neill Reid, updated 11/5/2006