This week on HST

HST Programs: June 11 - June 17, 2007

Program Number Principal Investigator Program Title Links
10792 Matthias Dietrich, The Ohio State University Research Foundation Quasars at Redshift z=6 and Early Star Formation History Abstract
10800 Keith Noll, Space Telescope Science Institute Kuiper Belt Binaries: Probes of Early Solar System Evolution Abstract
10818 Judith Cohen, California Institute of Technology Very Young Globular Clusters in M31 ? Abstract
10829 Paul Martini, The Phio State University Secular Evolution at the End of the Hubble Sequence Abstract
10841 Rupali Chandar, Observatories of the Carnegie Institution of Washington A Proper Motion Search for Intermediate Mass Black Holes in Globular Clusters (2nd Epoch Observations) Abstract
10862 John Clarke, Boston University Comprehensive Auroral Imaging of Jupiter and Saturn during the International Heliophysical Year Abstract
10870 Mark R. Showalter, SETI Institute The Ring Plane Crossings of Uranus in 2007 Abstract
10880 Henrique Schmitt, Naval Research Laboratiry The host galaxies of QSO2s: AGN feeding and evolution at high luminosities Abstract
10890 Arjun Dey, National Optical Astronomy Observatories Morphologies of the Most Extreme High-Redshift Mid-IR-Luminous Galaxies Abstract
10902 Goran Ostlin, Stockholm University The Nearest Luminous Blue Compact Galaxies: A Window on Galaxy Formation Abstract
10908 Edo Berger, Carnegie Institution of Washington Gotcha (Gamma-ray bursts) Abstract
10927 Wei-Chun Jao, Georgia State University The Weight-Watcher Program for Subdwarfs Abstract
10928 John Subasavage, Georgia State University Research Foundation Calibrating Cosmological Chronometers: White Dwarf Masses Abstract
10996 Holland Ford, The Johns Hopkins University NICMOS J-band Imaging of Strongly Lensing Clusters Abstract
10998 Peter McCullough, Space Telescope Science Institute Exoplanet XO-1b: light curve and parallax Abstract
11079 Luciana Bianchi, The Johns Hopkins University Treasury Imaging of Star Forming Regions in the Local Group: Complementing the GALEX and NOAO Surveys Abstract
11080 Daniela Calzetti, University of Massachusetts Exploring the Scaling Laws of Star Formation Abstract
11081 Gisella Clementini, INAF, Osservatorio Astronomico di Bologna RR Lyrae stars in M31 Globular Clusters: How did the M31 Spiral Galaxy Form? Abstract
11083 Patrick Cote, Dominion Astrophysical Observatory The Structure, Formation and Evolution of Galactic Cores and Nuclei Abstract
11084 Dan Zucker, Institute of Astronomy, Cambridge Probing the Least Luminous Galaxies in the Local Universe Abstract
11157 Joseph H. Rhee, University of California - Los Angeles NICMOS Imaging Survey of Dusty Debris Around Nearby Stars Across the Stellar Mass Spectrum Abstract
11311 Kailash Sahu, Space Telescope Science Institute The high-amplification microlensing event OGLE-2007-BLG-224: a substellar lens in the Galactic disk or a low-mass stellar lens in the halo? Abstract

Some selected highlights

GO 10870: The Ring Plane Crossings of Uranus in 2007

Images of Uranus spanning 2000 to 2004, showing the rotation of the ring plane Like the other Solar System gas giants, Uranus not only has an extensive number of satellite moons, but also possesses a ring system. Unlike the other giant planets, Uranus has a polar obliquity of 98o degrees, so its equator is close to perpendicular to the ecliptic plane. Consequently, from our vantage point on Earth, we view the north and south poles alternately during Uranus' 84-year circling of the Sun. Midway between the polar apparitions, of course, we view Uranus' equatorial plane - and see the ring system edge-on. The next ring plane crossing will occur in May and August 2007. At this juncture, the denser and more prominent rings will almost disappear from view, providing an opportunity to search for small satellite "shepherd" moons. These moons are expected to be present, acting as gravitational delineators, defining the radial size of the individual rings. Besides searching for the shepherds, the current HST program will use the High Resolution Camera on ACS to measure the thickness of the rings, and study the colours of the recently discovered fainter rings.

GO 10908: Gotcha - Gamma-ray bursts at high redshifts

The life history of a gamma-ray burst Gamma ray bursts are described colloquially as the biggest bangs since the Big Bang. Originally detected by US spy satellites in the 1960s, these short-lived bursts of high energy radiation resisted characterisation for over 30 years. It is only within the last decade that the Galactic vs. Extragalactic debate on their origins has been setled in favour of the latter. Generically, gamma ray bursts are believed to originate in the death throes of an extremely massive star, as it collapses to form either a black hole or a highly magnetised neutron star. Most occur at moderate to high redshifts; indeed, GRBs have proven a surprisingly effective way of finding galaxies at very high redshifts. The aim of this program is to identify host galaxies at z > 6. Gamma ray bursts are, by their nature, unpredictable; consequently, the observations are made in Target of Opportunity mode. The proposal triggers with the detection of an appropriate burst by the Swift satellite, and couples multicolour HST NICMOS imaging with ground-based radio and optical follow-up observations to track its evolution over the following ~300 days. During the next week, NICMOS follow-up observations are scheduled of a GRB that was detected on 22 December 2006.

GO 11080: Exploring the Scaling Laws of Star Formation

Composite BVJ image of NGC 972, one of the galaxies targeted in this program Understanding the star formation process is crucial to our developing viable theories of galaxy formation. The present program aims to investigate this process by obtaining NICMOS Paschen-alpha images of the central regions of an all-sky sample 84 nearby spiral and S0 galaxies. The near-infrared images will be combined with CO and HI interferometric radio maps, and, where such data are available, mid-infrared imaging by Spitzer, probing the relative distributions of gas, dust and star formation in these galaxies. In addition to studying how the star formation rate (SFR) varies as a function of gas density, the NICMOS data will permit high spatial-resolution investigations of where (and whether) Schmidt-type star-formation "laws" (power-law relations between the SFR and gas density) are valid in external galaxies.

GO 11310: The high-amplification microlensing event OGLE-2007-BLG-224: a substellar lens in the Galactic disk or a low-mass stellar lens in the halo?

A microlensed souce in the Galactic bulge 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. These wide-field imaging surveys target high density starfields towards the Magellanic Clouds and the Galactic Bulge, and have succeeded in identifying numerous lensing events. Statistical analysis, however, strongly suggests that the distribution of event durations and the overall number of lenses are inconsistent with a dark matter component. In particular, most, perhaps all, Bulge events are probably generated by normal stellar and brown dwarf members of the Galactic disk passing in front of a more distant Bulge star. Under those circumstances, it can become possible to directly detect both the background source and the lens if we allow sufficient time for the relative motion to separate the two images. (This has already been achieved for one LMC source, MACHO 5, where HST observations, taken 10 years after the lensing event, reveal the lens as a foreground red dwarf.) The present program aims to detect the lens for Bulge event, OGLE-2007-BLG-224/MOA-2007-BLG-163. The is the strongest lensing event detected so far, with a maximum amplification of ~4,000-fold. Based on the timescale of the light curve, the lens is either a low-mass M dwarf/subdwarf or a brown dwarf. HST images are being taken with WFPC2 this coming week as a reference. The field will be re-observed in ~6 months, when the lens should be separated from the source. If the lensing object is an M dwarf, then it will clearly visible on the second epoch images.

Past weeks:
page by Neill Reid, updated 23/4/2007