This week on HST

HST Programs: January 5, 2008 - January 11, 2009

Program Number Principal Investigator Program Title Links
11130 Luis Ho, Carnegie Institution of Washington AGNs with Intermediate-mass Black Holes: Testing the Black Hole-Bulge Paradigm, Part II Abstract
11236 Harry Teplitz, California Institute of Technology Did Rare, Large Escape-Fraction Galaxies Reionize the Universe? Abstract
11612 Kris Davidson, University of Minnesota - Twin Cities Eta Carinae's Continuing Instability and Recovery - the 2009 Event Abstract
11704 Brian Chaboyer, Dartmouth College The Ages of Globular Clusters and the Population II Distance Scale Abstract
11785 Howard E. Bond, Space Telescope Science Institute Trigonometric Calibration of the Distance Scale for Classical Novae Abstract
11789 George Fritz Benedict, University of Texas at Austin An Astrometric Calibration of Population II Distance Indicators Abstract
11944 Douglas R. Gies, Georgia State University Research Foundation Binaries at the Extremes of the H-R Diagram Abstract
11962 Adam Riess, The Johns Hopkins University A New Supernova in the Antennae; Narrowing in on the Hubble Constant and Dark Energy Abstract
11966 Michael W. Regan, Space Telescope Science Institute The Recent Star Formation History of SINGS Galaxies Abstract
11967 Rachel Somerville, Space Telescope Science Institute WFPC2 Imaging of the Lockman Hole Abstract

Selected highlights

GO 11130: AGNs with Intermediate-mass Black Holes: Testing the Black Hole-Bulge Paradigm, Part II

Schematic diagram of an active galacioc nucleus Active galaxies are characterised by bright, compact nuclei that are the source of strong emission lines due highly ionised material. These phenomena are generally believed to arise in hot gas in an accretion disk, centred on a massive (>106 solar mass) hole; indeed, detailed kinematics for a handful of objects have confirmed the presence of a compact, massive object in the core. Most active galactic nuclei (AGNs) are found in spiral galaxies that possess at least a moderately prominent bulge. The present aims to determine whether AGNs exist within later-type spirals, with less prominent bulge components. At the same time, the proposers hope to probe the lower mass limit for black hole formation, specifically testing whether significant numbers of intermediate-mass (~105 colar mass) black holes form. To eamine this issue, this proposal targets lower luminosity galaxies, using WFPC2 to obtain I-band (F814W) images of AGNs selected from SDSS spectroscopy. Those images will be used to characterise the nuclear morphology and determine bulge/disk ratios.

GO 11789: 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 to a 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 11944: Binaries at the Extremes of the H-R Diagram

The MV-mass relation for low-mass stars (from T. Henry) The mass-luminosity relation remains one of the key underpinnings of stellar astrophysics, notably in probing the grey area that separates hydrogen-burning stars from cooling-powered brown dwarfs. The calibration of thsi relation rests on observations of binary systems, primarily eclipsing binaries at masses above 1 MSun, and primarily astrometric binaries at sub-solar masses. In the latter case, reliable mass determinations require orbital measurements of extremely high accuracy, which, in turn, requires high precision astrometry over at least one orbital period. The Fine Guidance Sensors on HST have proven invaluable in this regard, since they permit both the detection of closely-separated binary systems, and sub-milliarcsecond accuracy astrometry of resolved binary systems with sub-arcsecond separations; in other words, HST allows measurement of nearby, low-mass binaries with periods short enough to allow completion of the observations in significantly less than an astronomer's lifetime.
The current program is using the FGS to search for new binary systems among the more extreme constituents of the HR diagram: specifically, massive, luminous O stars; nearby lower main-sequence K and M dwarfs and subdwarfs; and cool white dwarfs. Suitable binary systems detected through these initial observations will be targeted for detailed monitoring in subsequent observational programs

Past weeks:
page by Neill Reid, updated 1/10/2008