This week on HST

HST Programs: October 30 - November 5, 2006

Program Number Principal Investigator Program Title Links
10494 Leon Koopmans, Kapteyn Institute Imaging the mass structure of distant lens galaxies Abstract
10496 Saul Perlmutter, Lawrence Berkeley National Laboratory Decelerating and Dustfree: Efficient Dark Energy Studies with Supernovae and Clusters Abstract
10508 William Grundy, Lowell Observatory Orbits, Masses, and Densities of Three Transneptunian Binaries Abstract
10551 Shri Kulkarni, California Institute of Technology Gamma-Ray Bursts from Start to Finish: A Legacy Approach Abstract
10556 David Turnshek, University of Pittsburgh Neutral Gas at Redshift z=0.5 Abstract
10588 Michael Brotherton, University of Wyoming The Host Galaxies of Post-Starburst Quasars Abstract
10624 Derek B. Fox, California Institute of Technology Solving the Mystery of the Short-Hard Gamma-Ray Bursts Abstract
10632 Massimo Stiavelli, Space Telescope Science Institute Searching for galaxies at z>6.5 in the Hubble Ultra Deep Field Abstract
10703 Harald Ebeling, University of Hawaii Life in the fast lane: The dark-matter distribution in the most massive galaxy clusters in the Universe at z>0.5 Abstract
10792 Matthias Dietrich, The Ohio State University Research Foundation Quasars at Redshift z=6 and Early Star Formation History Abstract
10800 Keith Noll, Space Telescope Science Institute Kuiper Belt Binaries: Probes of Early Solar System Evolution Abstract
10801 Keith Noll, Space Telescope Science Institute Direct Determination of Kuiper Belt Object Diameters with HST Abstract
10802 Adam Riess, Space Telescope Science Institute SHOES-Supernovae, HO, for the Equation of State of Dark energy Abstract
10813 David Bowen, Princeton University MgII Absorption Line Systems: Galaxy Halos or the Metal-Enriched IGM? Abstract
10829 Paul Martini, The Ohio State University Secular Evolution at the End of the Hubble Sequence Abstract
10833 Bradley Peterson, The Ohio State University Research Foundation Host Galaxies of Reverberation Mapped AGNs Abstract
10843 Michael Corbin, United States Naval Observatory Deep Imaging of Extremely Metal-Poor Galaxies Abstract
10849 Stanimir Metchev, University of California - Los Angeles Imaging Scattered Light from Debris Disks Discovered by the Spitzer Space Telescope around 21 Sun-like Star Abstract
10853 Linda Smith, University College London M82 as a Fossil Starburst: Probing the Super Star Cluster Content of Region B Abstract
10860 Michael Brown, California Institute of Technology The largest Kuiper belt objects Abstract
10876 Jean-Paul Kneib, Observatoire de Marseille SL2S: The Strong Lensing Legacy Survey Abstract
10877 Weidong Li, University of California - Berkeley A Snapshot Survey of the Sites of Recent, Nearby Supernovae Abstract
10878 John O'Meara, The Pennsylvania State University An ACS Prism Snapshot Survey for z~2 Lyman Limit Systems Abstract
10882 William Sparks, Space Telescope Science Institute Emission Line Snapshots of 3CR Radio Galaxies Abstract
10886 Adam Bolton, Smithsonian Institution Astrophysical Observatory The Sloan Lens ACS Survey: Towards 100 New Strong Lenses Abstract
10893 Peter Garnavich, University of Notre Dame Sweeping Away the Dust: Reliable Dark Energy with an Infrared Hubble Diagram Abstract
10905 R. Tully, University of Hawaii The Dynamic State of the Dwarf Galaxy Rich Canes Venatici I Region Abstract
10911 John P. Blakeslee, Washington State University Calibration of ACS F814W Surface Brightness Fluctuations Abstract
10920 Charles Hoopes, The Johns Hopkins University High-Resolution Imaging of Nearby Lyman Break Galaxy Analogs in the GALEX All-Sky Survey Abstract
10922 Giampaolo Piotto, Universita di Padova Searching for Signs of a Double Generation of Stars in Galactic Globular Clusters Abstract

Some selected highlights

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 netron 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 10843: Deep Imaging of Extremely Metal-Poor Galaxies

ACS HST image of I Zwicky 18, the archetypical metal-poor dwarf galaxy In standard cosmologies, big bang nucleosynthesis is responsible for the production of hydrogen, helium and a trace abundance of lithium. The first stars - and the first galaxies - formed from this near-pristine material, and stellar nucleosynthesis accounts for the production of heavier elements (`metals', in astronomical parlance). As stars evolve and die, they return processed material to the interstellar medium, enriching the metal content and increasing the metallicity of subsequent stellar generations. Thus, within the Milky Way, the stars in the stellar halo (age 11-13 Gyrs) are 10 to 1000 times more metal-poor than the Sun's neighbours in the Galactic Disk. However, a small number of dwarf galaxies are known that seem to have lain fallow, avoiding star formation and self-enrichment, for almost a Hubble time. The classic example is the dwarf galaxy I Zwicky 18, with a metallicity of [M/H]~-1.2; analyses of recent HST ACS observations suggest an age of only 500 Myrs for the dominant stellar population. Nonetheless, the non-primodial abundances indicates that these systems have experienced previous star formation. The present program targets another dwarf system, CGCG 269-049, for deep ACS observations with the aim of searching for an underlying population of evolved stars, produced by a prior star formation episode (or episodes), and searching for dynamical features and young star clusters.

GO 10860: The largest Kuiper Belt Objects

The view from sedna: an artist's impression The Kuiper Belt lies beyond the orbit of Neptune, extending from ~30 AU to ~50 AU from the Sun, and includes at least 70,000 objects with diameters exceeding 100 km. Setting aside Pluto, the first trans-Neptunian objects were discovered in the early 1990s. Most are relatively modest in size, with diameters of a few hundred km and photometric properties that suggested an icy composition, similar to Pluto and its main satellite, Charon. Over the last three years, however, a handful of substantially larger bodies have been discovered, with diameters of more than 1000 km; one of the objects, 2003 UB313, is comparable in size to Pluto (2320 km.). These recent results, of course, were one of the main stimuli for the IAU's recent revision of Pluto's status from planet to `dwarf planet' - an issue that still remains contentious in some quarters. However, regardless of spats over nomenclature, it is clear that these objects (ice planets?) are a significant component in the outer Solar System. Both HST and the Spitzer infrared space telescope have played an important role in these recent investigations, measuring the angular diameter of the larger KBOs, and the albedo over a wide range of wavelengths. The aim of the present set of observations is to target ~20 trans-Neptunian objects, using red (F606W) images and low-resolution spectra, obtained with the High Resolution Camera on the Advanced Camera for Surveys, to probe their size and chemical composition.

GO 10922: Searching for Signs of a Double Generation of Stars in Galactic Globular Clusters

The complex globular cluster, Omega Centauri Omega Centauri is one the most intriguing members of the galactic globular cluster system. With a mass of ~5 x 106 MSun, Omega Cen is about ten times more massive than the typical large globular. In addition, it has long been known to show a substantial range in chemical abundance, unlike the homogeneous characteristics of other clusters. Finally, both ground-based (CTIO observations by Lee et al, 1999) and HST (Piotto & collaborators, 2004) imaging have revealed significant complexity in the colour-magnitude diagram, suggestive of several distinct episodes of star formation. In particular, the HST observations suggest the presence of two distinct main sequences, with different chemical composition and age. These features are more characteristic of a dwarf galaxy than a single star-burst globular cluster, and there have been repeated suggestions over the years that the cluster we call Omega Cen is the stripped core, the product of a merger with the Milky Way. The present observational program will build on the previous HST investigations, using ACS to obtain high-precision photometry of main sequence stars, allowing a detailed assessment of the relative composition and age of the two major components.

Past weeks:
page by Neill Reid, updated 27/10/2006