This week on HST


HST Programs: December 25 - December 31, 2006

Program Number Principal Investigator Program Title Links
10584 Andreas Zezas, Smithsonian Institution Astrophysical Observatory The link between X-ray source and stellar populations in M81 Abstract
10587 Adam Bolton, Smithsonian Institution Astrophysical Observatory Measuring the Mass Dependence of Early-Type Galaxy Structure Abstract
10605 Evan Skillman, University of Minnesota - Twin Cities /td> Quantifying Star Formation and Feedback: The M81 Group Dwarf Galaxies Abstract
10797 Knud Jahnke, Max-Planck-Institut fur Astronomie, Heidelberg HE0450-2958: Lonesome black hole, scantly dressed quasar or massively dust obscured host galaxy? Abstract
10802 Adam Riess, Space Telescope Science Institute SHOES-Supernovae, HO, for the Equation of State of Dark energy Abstract
10813 David Bowen, Princeton University MgII Absorption Line Systems: Galaxy Halos or the Metal-Enriched IGM? Abstract
10842 Kem Cook, Lawrence Livermore National Laboratory A Cepheid Distance to the Coma Cluster Abstract
10847 Dean Hines, Space Science Institute Coronagraphic Polarimetry of HST-Resolved Debris Disks Abstract
10852 Glenn Schneider, University of Arizona Coronagraphic Polarimetry with NICMOS: Dust grain evolution in T Tauri stars Abstract
10858 Lin Yan, California Institute of Technology NICMOS Imaging of the z ~ 2 Spitzer Spectroscopic Sample of Ultraluminous Infrared Galaxies Abstract
10875 Harald Ebeling, University of Hawaii A Snapshot Survey of The Most Massive Clusters of Galaxies Abstract
10877 Weidong Li, University of California - Berkeley A Snapshot Survey of the Sites of Recent, Nearby Supernovae Abstract
10881 Graham Smith, University of Birmingham The Ultimate Gravitational Lensing Survey of Cluster Mass and Substructure Abstract
10882 William Sparks, Space Telescope Science Institute Emission Line Snapshots of 3CR Radio Galaxies Abstract
10886 Adam Bolton, Smithsonian Institution Astrophysical Observatory The Sloan Lens ACS Survey: Towards 100 New Strong Lenses Abstract
10890 Arjun Dey, National Optical Astronomy Observatories Morphologies of the Most Extreme High-Redshift Mid-IR-Luminous Galaxies Abstract
10894 Kelsey Johnson, The University of Virginia Probing the Birth of Super Star Clusters with NICMOS Abstract
10896 Paul Kalas, University of California - Berkeley An Efficient ACS Coronagraphic Survey for Debris Disks around Nearby Stars Abstract
10910 John A. Biretta, Space Telescope Science Institute HST / Chandra Monitoring of a Dramatic Flare in the M87 Jet Abstract
10915 Julianne Dalcanton, University of Washington ACS Nearby Galaxy Survey Abstract
10918 Wendy Freedman, Carnegie Institution of Washington Reducing Systematic Errors on the Hubble Constant: Metallicity Calibration of the Cepheid PL Relation Abstract
10990 Howard E. Bond, Space Telescope Science Institute Dynamical Masses and Third Bodies in the Sirius System Abstract

Some selected highlights

GO 10605: Quantifying Star Formation and Feedback: The M81 Group Dwarf Galaxies

The M81 galaxy group The M81 group is a loose collection of approximately 20 galaxies centred on the interacting pair M81, a spiral, and M82, the well-known starburst galaxy. The group lies at a distance of ~4 Mpc, and was targeted for Cepheid observations as part of the HST H0 Key Project.
This program will use ACS to survey 10 group members, chosen to span a factor of ~150 in luminosity, ~1000 in star formaton rate and a factor of 3 in metallicity. The ACS F555W and F814W (V, I) images will be used to study the recent star formation history, probing the last 500 Myrs with a time-resolution acccuracy of 5-10%. The goal is to investigate the extent and efficiency of feedback mechanisms in the ISM, notably examining the fraction of star formation triggered by feedback, the relative numbers of clusters and associations, and the role played by feedback from previous star formation episodes.

GO 10802: SHOES-Supernovae, HO, for the Equation of State of Dark energy

WFPC2 image of NGC 4639, one of the spirals targeted in this program The cosmic distance scale and dark energy are two key issues in modern astrophysics, and HST has played a vital role in probing both. On the one hand, HST has been involved in cosmic distance measurements since its inception, largely through the H0 Key Project, which used WFPC2 to identify and photometer Cepheids in 31 spiral galaxies at distances from 60 to 400 Mpc. On the other, HST is the prime instrument for investigating cosmic acceleration by searching for and following Type Ia supernovae at moderate and high redshift. These two cosmological parameters are directly related, and recent years have seen renewed interest in improving the accuracy of H0 with the realization that such measurements, when coupled with the improved constraints from the Cosmic Microwave Background, provide important constraints on cosmic acceleration and the nature of Dark Energy. The present HST program combines observations that are designed to tackle both questions. NICMOS will be used to observe known Cepheids in several Key Project spirals that have hosted Type Ia supernovae; the near-infrared data will provide more accurate distance estimates for those galaxies, tying together the Cepheid and SN Ia distance scales. At the same time, the ACS/WFC will be used for parallel observations designed to search for high-redshift supernovae. Follow-up observations of those discoveries will add further weight to the measurement of cosmic acceleration.

GO 10847: Coronagraphic Polarimetry of HST-Resolved Debris Disks

HST ACS/HRC coronagraphic images of debris disks around two nearby stars The last decade has seen the identification of debris disks around a number of stars in the Solar neighbourhood. The coronagraphic capabilities available on HST have been particularly useful in this regards, since the lower background present in space-based observations offers significant advantages in detecting these low surface brightness features. Those observations are complemented by mid-infrared surveys (notably by Spitzer) of denser, warmer disks in young stars. The latter observations detect thermal emission from the dust grains, permitting some constraints to be set on the chemical composition. The present program aims to use polarimetric observations of debris disks to probe the distribution of grain sizes and the density distribution of dust in those somewhat older systems. Observations of the A0 star, HD 32297, and the G3 dwarf, HD 61005, are scheduled in the coming week.

GO 10990: Dynamical Masses and Third Bodies in the Sirius System

HST image of Sirius A and B (epoch 2005) Sirius B is the hot white dwarf companion to the Dog Star. Lying at a distance of only 2.6 parsecs (~8.6 l.y.; the fifth nearest star system and the nearest white dwarf), Sirius was originally identified as a double star in the early 1840s, when Friedrich Bessel's astrometry of the primary revealed residual orbital motion, with a ~50-year period. The companion remained undetected until 1862, when Alvin Clark finally resolved Sirius B through visual observations with the 18.5 inch refractor that he had recently installed in Dearborn Observatory. There have been persistent suggestions that the system includes a third companion; many rest on ancient descriptions of the system as red (which likely stem from atmospheric reddening when the star is at low altitudes, rather than a recent red giant phase). Recent observations with HST offer the tantalising suggestion of orbital perturbations that might stem from a much lower mass companion. This program aims to use HST for long-term astrometric monitoring, aiing to verify or refute this hypothesis.

Past weeks:
page by Neill Reid, updated 21/12/2006