This week on HST


HST Programs: August 27 - September 2, 2007

Program Number Principal Investigator Program Title Links
10599 Paul Kalas, University of California - Berkeley Multi-color imaging of two 1 Gyr old debris disks within 20 pc of the Sun: Astrophysical mirrors of our Kuiper Belt Abstract
10789 Christopher J. Conselice, University of Nottingham The Role of Environment in the Formation of Dwarf Galaxies Abstract
10818 Judith Cohen, California Institute of Technology Very Young Globular Clusters in M31 ? Abstract
10840 Nuria Calvet, University of Michigan The FUV fluxes of Tauri stars in the Taurus molecular cloud Abstract
10864 Carol A. Grady, Eureka Scientific Inc. Mapping the Gaseous Content of Protoplanetary and Young Planetary Systems with ACS Abstract
10884 Gray Wegner, Dartmouth College The Dynamical Structure of Ellipticals in the Coma and Abell 262 Clusters Abstract
10897 Jean-Francois Lestrade, Observatoire de Paris Coronagraphic imaging of the submillimeter debris disk of a 200Myr old M-dwarf Abstract
10915 Julianne Dalcanton, University of Washington ACS Nearby Galaxy Survey Abstract
11113 Keith S. Noll, Space Telescope Science Institute Binaries in the Kuiper Belt: Probes of Solar System Formation and Evolution Abstract
11140 Klaus Werner, Universitat Tubingen, Institut fur Astronomie & Astrophysik Can mass-ejections from late He-shell flash stars constrain convective/reactive flow modeling of stellar interiors? Abstract
11156 Kathy Rages, SETI Institute Monitoring Active Atmospheres on Uranus and Neptune Abstract
11172 Arlin Crotts, Columbia University Defining Classes of Long Period Variable Stars in M31 Abstract
11178 William M. Grundy, Lowell Observatory Probing Solar System History with Orbits, Masses, and Colors of Transneptunian Binaries Abstract
11196 Aaron S. Evans, State University of New York at Stony Brook An Ultraviolet Survey of Luminous Infrared Galaxies in the Local Universe Abstract
11206 Kai G. Noeske, University of California - Santa Cruz At the cradle of the Milky Way: Formation of the most massive field disk galaxies at z>1 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
11218 Howard Bond, Space Telescope Science Institute Snapshot Survey for Planetary Nebulae in Globular Clusters of the Local Group Abstract
11219 Alessandro Capetti, Osservatorio Astronomico di Torino Active Galactic Nuclei in nearby galaxies: a new view of the origin of the radio-loud radio-quiet dichotomy? Abstract
11289 Jean-Paul Kneib, Laboratoire d'Astronomie Spatiale SL2S: The Strong Lensing Legacy Survey Abstract
11329 Adam Riess, Space Telescope Science Institute The Final SHOE; Completing a Rich Cepheid Field in NGC 1309 Abstract

Some selected highlights

GO 10818: Very Young Globular Clusters in M31 ?

Hubble WFPC2 image of the brightest M31 globular cluster, Mayall II or G1 Galactic globular clusters are members of the halo stellar population in the Milky Way, with an approximately spherical spatial distribution. They typically have between 106 and 107 stellar members, and analysis of their colour-magnitude diagrams shows that they are old systems that formed during the first extensive period of Galactic star formation. Similar clusters have been found in many other galaxies, notably the nearest large spiral galaxy, M31. The first such clusters were identified by Hubble, in 1932, and several hundred are currently catalogued, exceeding the ~150 clusters in the Galactic system. Ground-based observations are only capable of resolving the brightest stars in the outskirts of these systems, but HST has allowed astronomers to construct colour-magnitude diagrams that extend beyond 27th magnitude, or ~1.5 magnitudes below the red clump or horizontal branch. As in the Galaxy, the overwhelming majority of these systems are clearly old. However, recent observations appeared to identify a number of star clusters with morphologies matching globular clusters, but extremely blue colours, consistent with much younger stellar populations. The aim of the present HST program is to use WFPC2 to image these candidate young globulars and verify their nature.

GO 11113: Binaries in the Kuiper Belt: Probes of Solar System Formation and Evolution

A composite of HST images of the Kuiper Belt binary, WW31 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 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. This proposal will use WFPC2 imaging of known KBOs to identify new binary systems.

GO 11196: An Ultraviolet Survey of Luminous Infrared Galaxies in the Local Universe

A NICMOS image of the interacting LIRG, NGC 6090 Luminous infrared galaxies (LIRGs) have total luminosities that exceed 1011.4 LSun, with most of the energy emitted at wavelengths longward of 10 microns. Many (perhaps most) of these galaxies are interacting or merging disk galaxies, with the excess infrared luminosity generated by warm dust associated with the extensive star formation regions. Many systems also exhibit an active nucleus, and may be in the process of evolving towards an S0 or elliptical merger remnant. The present program builds on a previous ACS survey of 88 systems from the IRAS Revised Bright Galaxy Sample (GO 10592) in the F439W and F814W passbands. The present program is using the ACS/SBC and WFPC2 to obtain far- (F140LP) and near- (F218W) UV imaging of 27 galaxies. Combined with the previously obtained B- and I-band data, these observations will probe
  • the distribution of star formation activity and the presence of bars and bridges, funneling gas towards active regions
  • the age distribution of star clusters
  • the relationship between star formation and AGN activity
  • the overall structural properties of the LIRGS as a function of luminosity and environment
The observations will also provide a detailed UV images for a reference sample of nearby galaxies. Observations of the interacting system, NGC 17, are scheduled for this week.

GO 11211: An Astrometric Calibration of Population II Distance Indicators

Measuring trigonometric parallax Trigonometric parallax measurement remains the fundamental method of determining distances to astronomical objects. The best ground-based parallax measurements can achieve accuracies of ~1 milliarcsecond, comparable with the typical accuracies achieved by the ESA Hipparcos astrometric satellite. This level of accuracy allows us to obtain reliable distances and luminosities for main sequence stars, subgiants, red giants and even a number of metal poor subdwarfs. However, with an effective distance limit of 100-150 parsecs, the sampling volume includes less than a handful of rarer, shorter-lived celestial objects. In particular, there are no RR Lyraes or Cepheids, two of the principal calibrators in the extragalactic distance scale. There is only one instrument currently available that can achieve astrometry of higher accuracy - the Fine Guidance Sensors (FGS) on HST. The present team used the FGS to measure a parallax of 3.82+/10.2 milliarseconds for RR Lyrae, the nearest star of its type. this corresponds toa distance of 262 parsecs. The present program aims to improve the calibration by extending observations to four more relatively nearby RR Lyraes (XZ Cyg, UV Oct, RZ Cep and SU Dra) and two Pop II Cepheids (Kappa Pav and VY Pyx).

Past weeks:
page by Neill Reid, updated 10/8/2007