This week on HST


HST Programs: July 30 - August 5, 2007

Program Number Principal Investigator Program Title Links
10854 Karl Stapelfeldt, Jet Propulsion Laboratory Coronagraphic Imaging of Bright New Spitzer Debris Disks II 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
11081 Gisella Clementini, INAF, Osservatorio Astronomico di Bologna RR Lyrae stars in M31 Globular Clusters: How did the M31 Spiral Galaxy Form? Abstract
11082 Christopher Conselice, Univ. of Nottingham NICMOS Imaging of GOODS: Probing the Evolution of the Earliest Massive Galaxies, Galaxies Beyond Reionization, and the High Redshift Obscured Universe Abstract
11084 Dan Zucker, Institute of Astronomy, Cambridge Probing the Least Luminous Galaxies in the Local Universe Abstract
11100 Marusa Bradac, Stanford University Two new `bullets' for MOND: revealing the properties of dark matter in massive merging clusters Abstract
11143 Andrew J. Baker, Rutgers the State University of New Jersey NICMOS imaging of submillimeter galaxies with CO and PAH redshifts Abstract
11169 Michael E. Brown, California Institute of Technology Collisions in the Kuiper belt 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
11188 Brian Siana, Jet Propulsion Laboratory First Resolved Imaging of Escaping Lyman Continuum Abstract
11202 Leon Koopmans, Kapteyn Astronomical Institute The Structure of Early-type Galaxies: 0.1-100 Effective Radii Abstract
11208 Tommaso L. Treu, University of California - Santa Barbara The co-evolution of spheroids and black holes in the last six billion years Abstract
11210 George Fritz Benedict, University of Texas at Austin The Architecture of Exoplanetary Systems Abstract
11292 Mark R. Showalter, SETI Institute The Ring Plane Crossings of Uranus in 2007 Abstract
11295 Howard E. Bond, Space Telescope Science Institute Trigonometric Calibration of the Distance Scale for Classical Novae Abstract

Some selected highlights

GO 10854: Coronagraphic Imaging of Bright New Spitzer Debris Disks - II

HST image of the face-on debris disk in the G2 dwarf, HD 107146 Planet formation occurs in circumstellar disks around young stars. Most of the gaseous content of those disks dissipates in less than 10 million years, leaving dusty debris disks that are detectable through reflect light at near-infrared and, to a lesser extent, optical wavelengths. The disk structure is affected by massive bodies (i.e. planets and asteroids), which, through dynamical interactions and resonances, can produce rings and asymmetries. Analysis of the rangle of morphological structure in these systems provides insight into the distribution of properties of planetary systems. HST currently provides the most effective means of achieving the high-contrast required for the detection of scattered light from these disks in the presence of the bright parent stars. To date, only a handful of systems have such observations. The present program aims to expand the sample by using Spitzer observations to identify nearby stars with excess flux at mid-infrared wavelengths - a signature of thermal radiation from circumstellar dust. The present proposal will use the NICMOS coronagraph to map the scattered light from those disks ay near-infrared wavelengths.

GO 11079: Treasury Imaging of Star Forming Regions in the Local Group: Complementing the GALEX and NOAO Surveys

The star forming region, N11, in the Small Magellanic Cloud Star formation is a complex process that takes place on many scales, from diffuse, low-level activity within dispersed clouds like the nearby Taurus association, through massive star forming regions, like Orion and 30 Doradus, to intense starbursts within galactic nucle and mergers. The aim of the present proposal is to use WFPC2 to survey a representative sample of active star-forming regions in local Group galaxies. In particular, the observations will cover a wide range of OB associations in the two nearest large spirals, the Andromeda galaxy, M31, and the Triangulum system, M33. Multicolour, high-resolution images, taken at passbands from the ultraviolet (F170W) to far-red (F814W) will allow H-R diagrams to be constructed, probing the distribution of ages and metallicities, and setting constraints on variations in the underlying initial mass function(s). In the coming week, observations are scheduled of OB associations in the M33.

GO 11169: Collisons in the Kuiper Belt

Visions of the Kuiper Belt 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 were 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; indeed, one object, Eris (2003 UB13), is slightly larger than Pluto (2320 km) and 25% more massive. We know the mass for Eris because it has a much lower mass companion, Dysnomia, which orbits Eris with a period of 16 days (see this recent press release ). Pluto, itself, has three companions: Charon, which is about 1/7th the mass of Pluto, and the much smaller bodies, Hydra and Nix, discovered from HST observations in early 2005. Observations of other Kuiper Belt Objects (KBOs), mainly using HST, reveal that a significant fraction are binary. This may indicate that the Kuiper Belt is a dangerous place to live, with frequent collisions between KBOs, leading to fragmentation and satellite formation. The present program aims to probe this issue through multi-wavelength observations of a wide range of KBOs.

GO 11188: First Resolved Imaging of Escaping Lyman Continuum

Lyman-break galaxy in the Hubble Deep Field: the four panels show the same region at (clockwise from upper left) 3000, 4500, 6060 and 8140 Angstroms; the centred object is a Lyman-break galaxy at z~3. In Big Bang cosmology, the early history of the unverise is characterised by three distinct phases: the initial expansion, during which time Big Bang nucleosynthesis occurs, and the universe cools from its initial exceedingly high temperatures; recombination, which occurs at a redshift z~1,100 (or an age of ~400,000 years), when the Universe was cool enough to allow neutral hydrogen to become dominant, leading to high opacity and the cosmic microwave background; and reionisation, when energy sources reionised hydrogen, reducing the opacity of the intergalactic medium and restoring transparency. Reionisation is generally believed to have occurred at a redshift between z~6 and z~20, with the ionising sources either (or both) the first generation of stars (Population III starbursts) and/or proto-quasars. The IGM remains ionised thereafter. A key issue in developing an understanding of this process is assessing how readily Lyman-alpha emission escapes from galaxies, and how starbursts contribute to reionisation at intermediate redshifts. The present program aims to address this issue through multiwavelength observations of several Lyman Break Galaxies (LBGs) at redshifts z~3. These galaxies have been identified because they "drop out" (disappear) at wavelengths shortward of the (redshifted) Lyman limit (912 Angstroms in the galaxy's rest frame). This program will combine deep F336W WFPC2 observations, covering the (redshifted) ionising radiation, with F606W data, sampling the continuum at (rest frame) 1500 Angstroms.

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