This week on HST

HST Programs: April 28 - May 4, 2008

Program Number Principal Investigator Program Title Links
10884 Gray Wegner, Dartmouth College The Dynamical Structure of Ellipticals in the Coma and Abell 262 Clusters 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
11117 David Kent Sing CNRS, Institut d'Astrophysique de Paris The Search for Atmospheric Water in the Transiting Planet HD189733b Abstract
11120 Daniel Wang, University of Massachusetts A Paschen-Alpha Study of Massive Stars and the ISM in the Galactic Center Abstract
11130 Luis Ho, Carnegie Institution of Washington AGNs with Intermediate-mass Black Holes: Testing the Black Hole-Bulge Paradigm, Part II Abstract
11131 Walter Jaffe, Sterrewacht Leiden Star formation at large radii in cooling flow brightest cluster galaxies Abstract
11136 Michael C. Liu, University of Hawaii Resolving Ultracool Astrophysics with Brown Dwarf Binaries Abstract
11142 Lin Yan, California Institute of Technology Revealing the Physical Nature of Infrared Luminous Galaxies at 0.3 Abstract
11159 R. Michael Rich, University of California - Los Angeles The True Galactic Bulge Luminosity Function Abstract
11160 Johan Richard, California Institute of Technology Escape fraction and stellar populations in a highly magnified Lyman-Break Galaxy Abstract
11166 Jong-Hak Woo, University of California - Santa Barbara The Mass-dependent Evolution of the Black Hole-Bulge Relations 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
11200 Philip Kaaret, University of Iowa An Ultraluminous EUV Source? Abstract
11202 Leon Koopmans, Kapteyn Astronomical Institute The Structure of Early-type Galaxies: 0.1-100 Effective Radii 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
11214 John Wisniewski, NASA Goddard Space Flight Center HST/FGS Astrometric Search for Young Planets Around Beta Pic and AU Mic Abstract
11220 Jeff Cooke, University of California - Irvine Direct Detection and Mapping of Star Forming Regions in Nearby, Luminous Quasars Abstract
11225 C. S. Kochanek, The Ohio State University Research Foundation The Wavelength Dependence of Accretion Disk Structure Abstract
11233 Giampaolo Piotto, Universita di Padova Multiple Generations of Stars in Massive Galactic Globular Clusters Abstract
11235 Jason A. Surace, California Institute of Technology HST NICMOS Survey of the Nuclear Regions of Luminous Infrared Galaxies in the Local Universe Abstract
11312 Graham Smith, University of Birmingham The Local Cluster Substructure Survey (LoCuSS): Deep Strong Lensing Observations with WFPC2 Abstract
11352 Andrew Gould, The Ohio State University Research Foundation Mass and distance of the sub-Saturn microlensing planet OGLE-2007-BLG-349Lb Abstract
11495 Carole A. Haswell, Open University The first direct detection of an extrasolar planetary stratosphere? /td> Abstract

Some selected highlights

GO 11107: Imaging of Local Lyman Break Galaxy Analogs: New Clues to Galaxy Formation in the Early Universe

Mosaic of HST images of M82, the best-known starburst galaxy Current Big Bang cosmological models predict that the universe should have undergone a global re-ionisation at redshifts between 6 and 20. The first generation of stars is generally tapped as the most likely source of the ionising radiation, perhaps enhanced through merger-stimulated starbursts. Direct observations of those galaxies are not possible at present; the James Webb Space Telescope is expected to open up observations of these systems. In consequence, there is considerable interest in identifying galaxies at lower redshifts that could serve as analogues for the z>6 systems. Over the last few years, the Galaxy Evolution Explorer (GALEX) has proved an important new tool in identifying candidate objects. GALEX has conducted an all-sky survey at ultraviolet wavelengths, and has uncovered sigificant numbers of UV luminous galaxies at low and moderate redshifts. Many of these galaxies are starbursts, undergoing substantial outbursts of star formation. These galaxies have been categorised as "compact UV luminous galaxies" (UVLGs). These appear to be galaxies that are undergoing small-scale mergers, leading to extensive dissipation and vigorous star formation. The present program is using the ACS/SBC prism and WFPC2 to obtain ultraviolet spectra and R-band images of 31 systems, probing the star formation history and its variation with environment.

GO 11136: Resolving Ultracool Astrophysics with Brown Dwarf Binaries

NICMOS images of the ultracool L/T binary, 2MASS J22521073-1730134; the northern component, notably fainter at F160W, is the T dwarf. Ultracool dwarfs are defined as having spectral types later than M7, and therefore include the recently discovered L and T dwarfs. They encompass the lowest mass stars (masses < ~0.1 MSub) and sub-stellar mass brown dwarfs, with surface temperatures ranging from ~2500K (~M7) to ~700K (late-type T dwarfs). Following their discovery over a decade ago, considerable theoretical attention has focused on the evolution of their intrinsic properties, particularly the details of the atmospheric changes in the evolution from type L to type T. This point marks the emergence of methane as a dominant absorber at near-infrared wavelengths. Current models suggest this transition occurs at ~1400-1200K, and that the spectral changes are at least correlated with, and perhaps driven by, the distribution and properties of dust layers ("clouds"). The overall timescales associated with this process remains unclear. The present proposal aims to tackle this issue through observations of ultracool binary systems. Since these systems are almost certainly coeval, the relative spectral energy distributions of the two components can be used to set constraints on evolutionary models. More than 40 ultracool binary systems are currently known; almost all have relatively small linear separations (<15 AU), and components with mass ratios close to one. The present program targets 13 systems with spectral types near the L/T boundary.

GO 11210: The Architecture of Exoplanetary Systems

Artist's impression of a young planetary system Immanuel Kant is generally credited with first proposing that the planets in the Solar System coalesced from a flat, rotating disk formed by the Solar Nebula. Direct confirmation of that process only came in the early 1990s, when millimetre-wave interferometers were able to detect molecular gas in Keplerian rotation around a handful of nearby young stars. Since then, there have been numerous other observations, including Hubble's images of proplyds (protoplanetary disks) in the Orion Cluster, and Hubble and Spitzer observations of edge-on disks in other young stars. One of the clear selling points of the Solar Nebula disk model is that it appears to offer a natural path to forming planets with coplanar orbits, matching (most of) our observations of the Solar System. On the other hand, as our knowledge of exoplanetary systems has accumulated over the last decade, it has become clear that dynamical interactions may play a very important role in the evolution of these systems. In particular, disk/planet interactions are generally regarded as responsible for the inward migration of gas giants to form hot Jupiters in <3 day period orbits. Planet-planet interactions could lead to significant changes in orbital inclination. Radial velocity planet searches are uncovering more and more multi-planet systems. This program focuses the high precision of HST's astrometric detectors, the Fine Guidance Sensors, on four of those systems. The aim is to complement the existing radial velocity measurements with sub-milliarcsecond precision astrometry, allowing determination of the true orbital paths - specifically, the relative inclination - of the low-mass objects in these systems.

GO 11225: The Wavelength Dependence of Accretion Disk Structure

The first Einstein cross, the gravitational lensed QSO, G2237+0305 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 to probe the mass distributions on a variety of scales: of galaxies (primarily via multiply-imaged quasars); of galaxy clusters (arcs and arclets); and at the largest scales (weak lensing). However, lensing can also provide insight on the small-scale properties of the object being lensed. In a lensed QSO, the light from the QSO follows different paths to produce the separate images; each of those paths has a different length; consequently, flux variations in the source show up at different times in the separate images. The present program aims to take advantage of this property to probe the structure of the accretion disks surrounding the central black hole in a number of lensed QSOs. The program will combine ultraviolet observations with the ACS/SBC on HST with Chandra X-ray data. Studying the variation as a function of wavelength should probe the accretion disk structure, since light from the inner regions are expected to dominate at shorter wavelengths, while the outer regions dominate at longer wavelengths.

GO 11352: Mass and distance of the sub-Saturn microlensing planet OGLE-2007-BLG-349Lb

The light curve of the OGLE-2005-BLG-390Lb microlensing event, Gravitational lensing is a consequence of general relativity, and the effects were originally quantified by Einstein himself in the mid-1920s. In the 1930s, Fritz Zwicky suggested that galaxies could serve as lenses, but lower mass objects can also also lens background sources. Bohdan Paczynski pointed out in the mid-1980s that this offered a means of detecting dark, compact objects that might contribute to the dark-matter halo. Paczcynski's suggestion prompted the inception of several large-scale lensing surveys, notably MACHO, OGLE, EROS and DUO - wide-field imaging surveys that target high density starfields towards the Magellanic Clouds and the Galactic Bulge. Numerous lensing events have been identified, although statistical analysis strongly suggests that neither the distribution of event durations nor the overall numbers are consistent with a dark matter component; however, the observations have resulted in unanticipated side benefits, notably the identification of planetary companions of several foreground lenses. All of these lenses are stars, and the main light amplification is produced by the changing lightpath through the stellar gravitational field. If the star has planetary companions, and if the orientation is appropriate, then the planet's gravitational field can produce a "blip" on the light curve. OGLE-2007-BLG-349Lb is the seventh planet discovered via this technique. This proposal aims to better understand the mass of the host star (and hence the mass of the planet) by using HST's high angular resolution to identify PSF differences in WFPC2 and NIC1 images taken in early October 2007 and early May this year.

Past weeks:
page by Neill Reid, updated 17/4/2008