This week on HST

HST Programs: December 10 - December 16, 2007

Program Number Principal Investigator Program Title Links
10812 Slawomir Piatek, New Jersey Institute of Technology Space Motions for the Draco and Sextans Dwarf Spheroidal Galaxies 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
10886 Adam Bolton, Smithsonian Institution Astrophysical Observatory The Sloan Lens ACS Survey: Towards 100 New Strong Lenses Abstract
10889 Roelof de Jong, Space Telescope Science Institute The Nature of the Halos and Thick Disks of Spiral Galaxies Abstract
10915 Julianne Dalcanton, University of Washington ACS Nearby Galaxy Survey Abstract
10928 John Subasavage, Georgia State University Research Foundation Calibrating Cosmological Chronometers: White Dwarf Masses Abstract
11000 Zoltan Balog, University of Arizona Evaporating Disks Abstract
11080 Daniela Calzetti, University of Massachusetts Exploring the Scaling Laws of Star Formation 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
11103 Harald Ebeling, University of Hawaii A Snapshot Survey of The Most Massive Clusters of Galaxies Abstract
11107 Timothy M. Heckman, The Johns Hopkins University Imaging of Local Lyman Break Galaxy Analogs: New Clues to Galaxy Formation in the Early Universe Abstract
11130 Luis Ho, Carnegie Institution of Washington AGNs with Intermediate-mass Black Holes: Testing the Black Hole-Bulge Paradigm, Part II Abstract
11142 Lin Yan, California Institute of Technology Revealing the Physical Nature of Infrared Luminous Galaxies at 0.3 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
11191 Wei-Hao Wang, Associated Universities, Inc. NICMOS Imaging of a z>4 High-Redshift Ultraluminous Submillimeter Source Abstract
11193 Wolfgang Brandner, University of California - Los Angeles A comprehensive study of the low-mass stellar population in the Galactic starburst region NGC 3603 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
11211 George Fritz Benedict, University of Texas at Austin An Astrometric Calibration of Population II Distance Indicators Abstract
11213 Gerard T. van Belle, California Institute of Technology Distances to Eclipsing M Dwarf Binaries Abstract
11215 Scott Anderson, University of Washington New Sightlines for the Study of Intergalactic Helium: Dozens of High-Confidence, UV-Bright Quasars from SDSS/GALEX Abstract
11226 Philippe Lamy, Laboratoire d'Astrophysique de Marseille Hubble Investigation of Comet 8P/Tuttle Abstract
11228 Peter McCullough, Space Telescope Science Institute Extrasolar Planet XO-2b Abstract
11306 Frederic J. Pont, Observatoire de Geneve Direct radius measurement of the Neptune-size transiting exoplanet GJ436b Abstract
11309 Jacob L. Bean, University of Texas at Austin Chemical Composition of an Exo-Neptune Abstract
11341 Sarah Gallagher, University of California - Los Angeles Lower Luminosity AGNs at Cosmologically Interesting Redshifts: SEDs and Accretion Rates of z~0.36 Seyferts Abstract

Some selected highlights

GO 10886: The Sloan Lens ACS Survey: Towards 100 New Strong Lenses

ACS images of galaxy-galaxy Einstein ring lenses from the Sloan survey Gravitational lensing is a consequence the theory of general relativity. Its importance as an astrophysical tool first became apparent with the realisation (in 1979) that the quasar pair Q0957+561 actually comprised two lensed images of the same background quasar. In the succeeding years, lensing has been used primarily to probe the mass distribution of galaxy clusters, using theoretical models to analyse the arcs and arclets that are produced by strong lensing of background galaxies, and the large-scale mass distribution, through analysis of weak lensing effects on galaxy morphologies. Gravitational lensing can also be used to investigate the mass distribution of individual galaxies. Until recently, the most common background sources were quasars. Galaxy-galaxy lenses, however, offer a distinct advantage, since the background source is extended, and therefore imposes a stronger constraints on the mass distribution of the lensing galaxy than a point-source QSO. The Sloan sky survey provides a powerful tool for identifying candidate galaxy-galaxy lenses; this program is using HST-ACS imaging to verify the nature of those candidates, and provide the angular resolution necessary to model the mass distribution.

GO 11175: UV Imaging to Determine the Location of Residual Star Formation in Galaxies Recently Arrived on the Red Sequence

Galaxy mergers and the red sequence

The overwhelming majority of galaxies are found in clusters. Observations show that almost all well-defined cluster systems at low and moderate redshift have a significant population of elliptical galaxies which have red colours, indicative of old stellar populations and minimal current star formation. The elliptical galaxies outline a distinct sequence in the colour-magnitude (or colour-mass) diagram, the so-called red sequence. Over the last few years, there has been considerable interest in understanding the origins of this sequence: how did the ellipticals form (most theories envisage mergers of gas-rich systems at moderate redshifts)? when did star formation cease in these galaxies (most galaxies in clusters at redshifts 1.5 < z < 3 seem to have active star formation)? are there environmentally-dependent effects? This proposal aims to address some of these questions through WFPC2 BVI and ACS/SBC observations of a number of low-redshift (0.04 < z , 0.10) galaxies that appear to have only recently arrived on the red sequence. The WFPC2 data will provide detailed morphologies, while the SBC ultraviolet imaging will be ued to search for traces of residual star formation.

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).

GO 11306: Direct radius measurement of the Neptune-size transiting exoplanet GJ436b

GO 11309: Chemical Composition of an Exo-Neptune

Models of the potential interior structure of Gl 436b Gliese 436 is an early-type M dwarf (spectral type M2.5) with a mass approximately 40% that of the Sun lying at a distance of ~10 parsecs. In August 2004, the Lick/Carnegie planet search team (led by Geoff Marcy and Paul Butler) announced the discovery of a ~22 Earth-mass planet in a 2.64 day orbit around this star. Unlike most "hot jupiters", this "hot Neptune" is on an elliptical orbit, e=0.16, which, with a semi-major axis of 0.0278 AU, brings it within 3.5 million kilometres of the central star. Gl 436 is significantly cooler than the Sun, with a surface temperature close to ~3400 degrees Kelvin; even so, the "surface" temperatures on Gl 436b are expected to reach ~740 K (~370 C). In May of this year, a team led by F. Pont demonstrated that Gl 436b transits the parent star. The initial ground-based observations allowed them to derive a diameter approximately 4 times that of Earth, directly comparable with Uranus and Neptune. This provides key insight into the likely origins of Gl 436b, since combining the diameter with the measured mass gives the mean density, and, by inference, the likely composition. For Gl 436b, the indications are that the planet is a displaced "ice giant". In the coming week, HST will observe the host star as part of two observational programs. In the first, GO 10306, le by members of the same team that discovered the planet, NICMOS observations will be used to obtain higher accuracy measurement of the planet's radius at near-infrared wavelenths. The second program, GO 10309, will use FGS to measure the transit light-curve, giving a precise estimate of the planetary radius at optical wavelengths. Combining the two results will set stronger contraints on the likely chemical composition.

Past weeks:
page by Neill Reid, updated 7/11/2007