This week on HST

HST Programs: September 13, 2010 - September 19, 2010

Program Number Principal Investigator Program Title
11563 Garth D. Illingworth, University of California - Santa Cruz Galaxies at z~7-10 in the Reionization Epoch: Luminosity Functions to <0.2L* from Deep IR Imaging of the HUDF and HUDF05 Fields
11598 Jason Tumlinson, Space Telescope Science Institute How Galaxies Acquire their Gas: A Map of Multiphase Accretion and Feedback in Gaseous Galaxy Halos
11668 Anna Frebel, Smithsonian Institution Astrophysical Observatory Cosmo-chronometry and Elemental Abundance Distribution of the Ancient Star HE1523-0901
11677 Harvey B. Richer, University of British Columbia Is 47 Tuc Young? Measuring its White Dwarf Cooling Age and Completing a Hubble Legacy
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
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 Search for Very High-z Galaxies with WFC3 Pure Parallel
11707 Kailash Sahu, Space Telescope Science Institute Detecting Isolated Black Holes through Astrometric Microlensing
11734 Andrew J. Levan, The University of Warwick The hosts of high redshift gamma-ray bursts
11737 David M. Meyer, Northwestern University The Distance Dependence of the Interstellar N/O Abundance Ratio: A Gould Belt Influence?
11741 Todd 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
11818 Paul Kalas, University of California - Berkeley NICMOS confirmation of an extrasolar planet candidate directly detected with ACS
11840 Andrew J. Levan, The University of Warwick Identifying the host galaxies for optically dark gamma-ray bursts
12019 Christy A. Tremonti, University of Wisconsin - Madison After the Fall: Fading AGN in Post-starburst Galaxies
12209 Adam S. Bolton, University of Utah A Strong Lensing Measurement of the Evolution of Mass Structure in Giant Elliptical Galaxies
12210 Adam S. Bolton, University of Utah SLACS for the Masses: Extending Strong Lensing to Lower Masses and Smaller Radii
12234 Wesley Fraser, California Institute of Technology Differentiation in the Kuiper belt: a search for silicates on icy bodies.
12239 Gilda E. Ballester, University of Arizona Springtime at Uranus: Upheaval in the Stratosphere?
12244 Joachim Saur, Universitat zu Koeln Mapping Ganymede's time variable aurora in the search for a subsurface ocean
12256 Sean A. Farrell, University of Leicester The Ultraviolet and Optical Counterparts of the Intermediate Mass Black Hole Candidate ESO 243-49 HLX-1
12265 Masami Ouchi, Carnegie Institution of Washington Determining the Physical Nature of a Unique Giant Lya Emitter at z=6.595
12292 Tommaso L. Treu, University of California - Santa Barbara SWELLS: doubling the number of disk-dominated edge-on spiral lens galaxies
12307 Andrew J. Levan, The University of Warwick A public SNAPSHOT survey of gamma-ray burst host galaxies
12316 John P. Wisniewski, University of Washington HST/FGS Astrometric Search for Young Planets Around Beta Pic and AU Mic
12320 Brian Chaboyer, Dartmouth College The Ages of Globular Clusters and the Population II Distance Scale
12324 C. S. Kochanek, The Ohio State University The Temperature Profiles of Quasar Accretion Disks

Selected highlights

GO 11677: Is 47 Tuc Young? Measuring its White Dwarf Cooling Age and Completing a Hubble Legacy

Hubble image of the globular cluster, 47 Tucanae Globular clusters are members of the Galactic halo population, which formed during the first extensive period of star formation in the Milky Way. As such, the properties of the 106 to 107 stellar constituents can provide crucial insight into the earliest stages of galaxy formation. Hubble has conducted a significant number of observing programs targeting these systems, with the majority designed to obtain moderately deep, multicolour imaging data of a range of clusters. Those programs probe evolved stars, on the red giant and horizotal branch, and generally extend no more than a few magnitudes below the main-sequence turnoff. A few clusters, however, have been studied in detail - specifically, the two nearest clusters, NGC 6397, an extremely metal-poor cluster, and M4, a moderately metal-rich systems; Omega Centauri, one of the most massive clusters, perhaps even the remnant core of a dwarf galaxy; and 47 Tucanae, one of the higher metallicity systems, lying in the foreground of the Small Magellanic Cloud. Deep imaging of NGC 6397 and M4 has succeeded in clear detecion of the white dwarf cooling sequence in those clusters, and those data have been used to derive age estimates. The present observation aims to obtain similar data for 47 Tucanae, permitting an estimate of the relative age of these three, disparate clusters.

GO 11734: The hosts of high redshift gamma-ray bursts

Artist's impression of a gamma-ray burst Gamma ray bursts are events that tap extraordinary energies (1045 to 1047 joules) in remarkably short periods of time. Several thousands bursts have been detected over the last 30+ years, and analyses indicate that they can be divided into two classes with durations longer or shorter than 2 seconds. The short bursts appear to release more high energy radiation, so the two subsets are known as long/soft and short/hard bursts.The short/hard bursts appear to arise from coalescing binary systems (probably pairs of neutron stars or black holes), but the long/soft bursts appear to originate in the collapse of very massive stars. The latter sources are therefore almost certainly associated with star formation, so they act as signposts to active star-forming regions in the high redshift universe. Many of these bursts are sufficiently bright that ground-based spectroscopic observations allow reliable measurement of the redshift. In many cases, ground-based observations at later epochs are insufficient to detect the underlying host galaxy, and characterise its properties. This program targets such systems at redshifts z>3, and aims to use WFC3 and ACS observations to reveal the host galaxy.

GO 11818: Confirmation of an extrasolar planet candidate directly detected with ACS

HST-ACS image of the planetary-mass companion of Fomalhaut Fomalhaut, or alpha Piscis Austrini, is one of the Sun's closest neighbours, an A-type star with a mass approximately twice that of the Sun and an age between 100 and 300 million years, lying at a distance of only ~7.7 parsecs. Observations with the IRAS satellite in the early 1980s revealed the presence of significant excess radiation at mid-infrared wavelengths, indicating the presence of substantial dust within a disk that is being irradiated by the luminous central star. Since then, observations of Fomalhaut and nearby stars of that ilk have led to a much more detailed characterisation of the debris disk phase. In particular, Spitzer has mapped warm dust in these systems, while HST imaging has provided exquisite resolution in reflected light. It is now recogised that debris disks are the evolutionary stage where planet formation has likely run to completion, the gas has fully dissipated but the disk remains well populated with dusty material spanning a wide range of sizes. Indeed, it is likely that this phase coincides with the heavy bombardment epoch within the Solar System. ACS imaging of Fomalhaut reveals extensive structure in the disk, notably a sharply-defined, eccentric inner edge to the disk, which led to the prediction of a ~Saturn-mass planet at that location. Subsequent ACS/HRC observations led to the identification of that planet, one of the first direct images of a "conventional" exoplanet. The exoplanet is variable at optical wavelengths, suggesting that the observed flux is not only contributed by reflected light from the planetary "surface". The present observations will use STIS, with the primary star placed behind the occulting, to obtain further data aimed at constraining those possibilities.

GO 12320: 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.

Past weeks:
page by Neill Reid, updated 12/8/2010