This week on HST

HST Programs: May 24, 2010 - May 30, 2010

Program Number Principal Investigator Program Title
11142 Lin Yan, California Institute of Technology Revealing the Physical Nature of Infrared Luminous Galaxies at 0.3
11202 Leon Koopmans, Kapteyn Astronomical Institute The Structure of Early-type Galaxies: 0.1-100 Effective Radii
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?
11520 James C. Green, University of Colorado at Boulder COS-GTO: QSO Absorbers, Galaxies and Large-scale Structures in the Local Universe.
11556 Marc W. Buie, Southwest Research Institute Investigations of the Pluto System
11557 Gabriela Canalizo, University of California - Riverside The Nature of low-ionization BAL QSOs
11565 Sebastien Lepine, American Museum of Natural History A search for astrometric companions to very low-mass, Population II stars
11567 Charles R. Proffitt, Computer Sciences Corporation Boron Abundances in Rapidly Rotating Early-B Stars.
11570 Adam Riess, The Johns Hopkins University Narrowing in on the Hubble Constant and Dark Energy
11579 Alessandra Aloisi, Space Telescope Science Institute The Difference Between Neutral- and Ionized-Gas Metal Abundances in Local Star-Forming Galaxies with COS
11591 Jean-Paul Kneib, Laboratoire d'Astrophysique de Marseille Are Low-Luminosity Galaxies Responsible for Cosmic Reionization?
11592 Nicolas Lehner, University of Notre Dame Testing the Origin{s} of the Highly Ionized High-Velocity Clouds: A Survey of Galactic Halo Stars at z>3 kpc
11598 Jason Tumlinson, Space Telescope Science Institute How Galaxies Acquire their Gas: A Map of Multiphase Accretion and Feedback in Gaseous Galaxy Halos
11601 Klaus Werner, Universitat Tubingen, Institut fur Astronomie & Astrophysik UV spectroscopy of the hot bare stellar core H1504+65
11606 Daniel P. Batcheldor, Florida Institute of Technology Dynamical Hypermassive Black Hole Masses
11608 Nuria Calvet, University of Michigan How Far Does H2 Go: Constraining FUV Variability in the Gaseous Inner Holes of Protoplanetary Disks
11650 William M. Grundy, Lowell Observatory Mutual Orbits, Colors, Masses, and Bulk Densities of 3 Cold Classical Transneptunian Binaries
11663 Mark Brodwin, Smithsonian Institution Astrophysical Observatory Formation and Evolution of Massive Galaxies in the Richest Environments at 1.5 < z < 2.0
11666 Adam J. Burgasser, University of California - San Diego Chilly Pairs: A Search for the Latest-type Brown Dwarf Binaries and the Prototype Y Dwarf
11667 Christopher W. Churchill, New Mexico State University Detailed Probing of a 3000 km/s Ly-alpha + Metal Line Absorption Complex Near Two Galaxies at z=0.67
11692 J. Christopher Howk, University of Notre Dame The LMC as a QSO Absorption Line System
11696 Matthew A. Malkan, University of California - Los Angeles Infrared Survey of Star Formation Across Cosmic Time
11698 Mary E. Putman, Columbia University in the City of New York The Structure and Dynamics of Virgo's Multi-Phase Intracluster Medium
11700 Michele Trenti, University of Colorado at Boulder Bright Galaxies at z>7.5 with a WFC3 Pure Parallel Survey
11702 Hao-Jing Yan, The Ohio State University Research Foundation Search for Very High-z Galaxies with WFC3 Pure Parallel
11704 Brian Chaboyer, Dartmouth College The Ages of Globular Clusters and the Population II Distance Scale
11710 John P. Blakeslee, Dominion Astrophysical Observatory The Extreme Globular Cluster System of Abell 1689: The Ultimate Test of Universal Formation Efficiency
11712 John P. Blakeslee, Dominion Astrophysical Observatory Calibration of Surface Brightness Fluctuations for WFC3/IR
11730 Nitya Jacob Kallivayalil, Massachusetts Institute of Technology Continued Proper Motions of the Magellanic Clouds: Orbits, Internal Kinematics, and Distance
11732 C. S. Kochanek, The Ohio State University Research Foundation The Temperature Profiles of Quasar Accretion Disks
11741 Todd M. Tripp, University of Massachusetts Probing Warm-Hot Intergalactic Gas at 0.5 < z < 1.3 with a Blind Survey for O VI, Ne VIII, Mg X, and Si XII Absorption Systems
11789 George Fritz Benedict, University of Texas at Austin An Astrometric Calibration of Population II Distance Indicators
11829 Alexander Brown, University of Colorado at Boulder Coronal and Transition Region Heating Due to Magnetic Activity on Metal-Poor Dwarf Stars
12021 Philip Kaaret, University of Iowa An Irradiated Disk in an Ultraluminous X-Ray Source
12051 Saul Perlmutter, University of California - Berkeley Cross Calibration of NICMOS and WFC3 in the Low-Count-Rate Regime
12077 David Jewitt, University of California - Los Angeles Monitoring the Aftermath of an Asteroid Impact Event

Selected highlights

GO 11598: How Galaxies Acquire their Gas: A Map of Multiphase Accretion and Feedback in Gaseous Galaxy Halos

A computer simulation of galactic gas accretion and outflow Galaxy formation, and the overall history of star formation within a galaxy, clearly depends on the presence of gas, and therefore on how gas is accreted, recycled, circulated through the halo and, perhaps, ejected back into the intergalactic medium. Tracing that evolutionary history is difficult, since gas passes through many different phases, some of which are easier to detect than others. During accretion and, probably, subsequent recycling, the gas is expected to be reside predominantly at high temperatures. The most effective means of detecting such gas is through ultraviolet spectroscopy, where gas within nearby systems can be detected as absorption lines superimposed on the spectra of more distant objects, usually quasars. The present program is using the Cosmic Origins Spectrograph to observe z>1 QSOs that lie at small angular separations from SDSS galaxies at redshifts between z=0.15 and 0.35. The sightlines run through the halos of the galaxies, and the QSOs therefore provide a pencilbeam backlight that probes hot gas in the foreground systems.

GO 11570: Narrowing in on the Hubble Constant and Dark Energy

A GALEX image of Messier 106 (NGC 4258), one of the galaxies targeted in this program The Hubble constant remains a key parameter in understanding cosmology and the evolution of the Universe. Refining measurements of H0 therefore still represents a vital means of probing the nature of dark energy. The present program aims to tackle this question by laying a firmer foundation to the SNe Ia distance scale. The WFC3 IR camera will be used to identify and characterise Cepheid variables in eight relatively nearby galaxies that have hosted Type Ia SNe. Cepheids have signficantly lower amplitude at near-infrared wavelengths, and the measured magnitudes are less subject to uncertainties due to foreground reddening and variations in metallicity. As a consequence, determining the mean apparent magnitude, and hence the period/apparent magnitude relation, is substantially more straightforward than at optical wavelengths. Matching the observed relation against reference stars from the LMC allows a more reliable determination of the distance to the parent galaxy, and hence a firmer zeropoint for the SNe Ia distance scale. The aim is to reduce the level of systematics in determinations oif H0 to the 3 percent level.

GO 11704: The Ages of Globular Clusters and the Population II Distance Scale

Hubble Heritage image of the globular cluster, M15 Globular clusters are the oldest structures within the Milky Way that are directly accessible to observation. They are relatively simple systems, with relatively simple colour-magnitude diagrams (albeit with some complexities adduced from recent HST observations, see GO 11233 ). Matching those CMDs against theoretical models allows us to set constraints on the age of the oldest stars in the Galaxy, and hence on the age of the Milky Way and the epoch of galaxy formation. However, the accuracy of those age determinations rest crucially on the accuracy of the cluster distance determinations. The clusters themselves lie at distances of several kpc at best, and tens of kpc at worst; thus, direct trigonometric parallax measurements must await microacrsecond astrometric missions. The classical method of deriving distances is main sequence fitting - using nearby stars, with similar chemical abundances and accurate parallax measurements, to map out the main sequence in absolute units, and then scaling the cluster data to fit. The problem with this method is that metal-poor subdwarfs are rare, so even Hipparcos was only able to obtain accurate distances to a handful of stars. The present program aims to improve the distance measurements by using the Fine Guidance Sensors on HST to determine sub-millarcsecond trigonometric parallaxes to 9 subdwarfs, almost doubling the sample available for MS fitting.

GO 11732: The Temperature Profiles of Quasar Accretion Disks

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 WFC3/UVIS camera on HST with GALEX UV data for 5 lenses spanning as broad range of black hole masses. 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.

Past weeks:
page by Neill Reid, updated 19/2/2010