This week on HST


HST Programs: September 18 - September 24, 2006

Program Number Principal Investigator Program Title Links
10432 George Benedict, University of Texas at Austin Precise Distances to Nearby Planetary Nebulae Abstract
10482 Howard Bond, Space Telescope Science Institute Trigonometric Calibration of the Period- Luminosity Relations for Fundamental and First-Overtone Galactic Cepheids Abstract
10496 Saul Perlmutter, Lawrence Berkeley National Laboratory Decelerating and Dustfree: Efficient Dark Energy Studies with Supernovae and Clusters Abstract
10517 Steven Pravdo, Jet Propulsion Laboratory Imaging Astrometrically-Discovered Brown Dwarfs Abstract
10547 Edward Fitzpatrick, Villanova University A SNAP Program to Obtain Complete Wavelength Coverage of Interstellar Extinction Abstract
10556 David Turnshek, University of Pittsburgh Neutral Gas at Redshift z=0.5 Abstract
10578 Ignasi Ribas, Institut d'Estudis Espacials de Catalunya Eclipsing Binaries in the Local Group: Calibration of the Zero-point of the Cosmic Distance Scale and Fundamental Properties of Stars in M31 Abstract
10632 Massimo Stiavelli, Space Telescope Science Institute Searching for galaxies at z>6.5 in the Hubble Ultra Deep Field Abstract
10761 Victoria Kaspi, McGill University The X-ray Spectral and Optical/IR Flux Variability in Magnetars Abstract
10793 Avishay Gal-Yam, California Institute of Technology A Survey for Supernovae in Massive High-Redshift Clusters 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
10847 Dean Hines, Space Science Institute Coronagraphic Polarimetry of HST-Resolved Debris Disks Abstract
10849 Stanimir Metchev, University of California - Los Angeles Imaging Scattered Light from Debris Disks Discovered by the Spitzer Space Telescope around 21 Sun-like Stars Abstract
10872 Harry Teplitz, California Institute of Technology Lyman Continuum Emission in Galaxies at z=1.2 Abstract
10878 John O'Meara, The Pennsylvania State University An ACS Prism Snapshot Survey for z~2 Lyman Limit Systems 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
10892 Peter Garnavich, University of Notre Dame Imaging Dust Near Type Ia Supernovae: A New Light Echo Candidate Abstract
10906 Sylvain Veilleux, University of Maryland The Fundamental Plane of Massive Gas-Rich Mergers: II. The QUEST QSOs Abstract
10915 Julianne Dalcanton, University of Washington ACS Nearby Galaxy Survey Abstract
10917 Derek Fox, The Pennsylvania State University Afterglows and Environments of Short-Hard Gamma-Ray Bursts Abstract
10997 Holland Ford, The Johns Hopkins University The Environmental Effects of Large Scale Structures Around the Galaxy Cluster RXJ0152.7-1357 at z=0.84 Abstract

Some selected highlights

GO 10482: Trigonometric Calibration of the Period- Luminosity Relations for Fundamental and First-Overtone Galactic Cepheids

Cepheids in the LMC: the original PLC Cepheids are the original distance indicator, and remain the primary calibrator for the extragalactic distance scale. Most investigations tie the zeropoint for the latter scale to the Large Magellanic Cloud, which has a large population of Cepheid variables that provide a well-populated period-luminosity-colour (PLC) relation. In the case of the Hubble H0 Key Project, the LMC distance modulus is set at 18.5, corresponding to a distance of ~50 kpc. However, a variety of studies using a variety of distance estimators give LMC distance molduli that range from 18.1 to 18.8 (~42 to ~58 kpc). Moreover, the average metallicity of the LMC Cepheids is somewhat lower than the average for the tyypical spiral galaxies that serve as the key links in the H0 chain. It is therefore important to Verify the LMC calibration using Galactic Cepheids. Unfortunately, there are few such variables within 500 parsecs (Polaris is the nearest, at ~130 parsecs), and, as a result, most have trigonometric parallaxes, even with Hipparcos, that are accurate to no better than 20%. Eventually, astrometric missions such as SIM and Gaia will nail down these distances and the Galactic PLC calibration. In the meantime, the Fine Guidance Sensors on HST are capable of an astrometric accuracy of ~0.2 milliarcseconds. This program targets nine Cepheids, spanning a range of period, and will provide a local calibration that will test the LMC zeropoint at the 0.05 magnitude level.

GO 10632: Searching for galaxies at z>6.5 in the Hubble Ultra Deep Field
The Hubble Ultra-Deep Field (the UDF) is the deepest image so far obtained of the Cosmos. The original program comprised 412 orbits directed at a single ACS field within the Chandra Deep Field-South (CDF-S) GOODS area. Those 412 orbits were divided among four filters - F435W (broad B-band: 56 orbits), F606W (broad V/R-band: 56 orbits), F775W (I-band: 150 orbits), and F850LP (z-band: 150 orbits). A further 144 orbits were devoted to a 3x3 grid of F110W (J) and F160W (H) NICMOS images covering the same field.(GO program 9803). NICMOS was also employed in parallel with the ACS observations to obtain deep J- and H-band images of adjacent fields. The present proposal devotes 204 orbits to new observations of the prime and parallel fields, but with HST inverted; thus, the program will obtain ACS imaging (in F606W, F775W and F750LP) of the parallel fields, and deeper NICMOS (F110W, F160W) data for part of the original ACS UDF. The primary goal of the program is identify candidate very high redshift (6.5 < z < 8.5) sources, using photometric redshifts derived by combining the optical and near-infrared photometric catalogues.

GO 10849: Imaging Scattered Light from Debris Disks Discovered by the Spitzer Space Telescope around 21 Sun-like Stars

HST ACS image of the face-on debris disk around the nearby G dwarf, HD 107146 While much debate has raged in recent months over exactly how to define a planet, there is very little debate in the astronomical community about where planets form: they form in circumstellar disks. During the earliest stages of their existence, the disks are dusty, gas-rich and high opacity; for example, see NICMOS images of T Tauri stars and IRAS sources and current HST proposals 10540, 10810 and 10864. After only ~10 million years, however, the gas dissipates, leaving a young planetary system with a rich content of dust, rocks, planetoids and planets. This period corresponds to the high bombardment phase in earth's history, when the Moon was formed. To the outside observer, the dusty disk has low surface brightness, and is much less prominent than the gaseous disk. HST can image these disks via scattered light at near-infrared and, in a few cases, optical wavelengths - probably the most spectacular example is Beta Pic (see the recent HST ACS images ) - but the most effective means of detection is to search for excess thermal radiation at mid-IR wavelengths with Spitzer. The present proposal is a follow-on to a Spitzer Legacy program that surveyed nearby G dwarfs. The aim is to use the NICMOS coronagraph to resolve the structure of the disks suspected to be present in these 21 nearby solar-type stars.

GO 10881: The Ultimate Gravitational Lensing Survey of Cluster Mass and Substructure

Lensing by the z=0.39 galaxy cluster Cl0024+16; the inset shows several reconstructions of the z=1.63 lensed object, based on separate analysis of the brighter lensed images in this HST image. Gravitational lensing supplies a powerful method of tracing the mass distribution in galaxy clusters; at the same time, the amplified the light from background galaxies provides a means of probing the early stages of galaxy formation. These measurements are particularly effective when X-ray imaging data are also available, allowing direct measurement of the mass density and distribution of the hot intracluster medium. This snapshot proposal aims to use the Wide Field Camera on ACS to observe the central regions of low redshift (0.15 < z < 0.3) clusters with the requisite Chandra observations. The HST images will allow the resolution of lensed arcs in the cluster cores (due to strong lensing) and characterisation of weak-lensing distortions of the image profiles of faint background galaxies. The frequency and detailed distribution (size, multiplicity, redshifts) of the strong lens systems sets strong constraints on the total mass content, and its structure, in the central regions of low-redshift clusters. Those results, in turn, constrain cluster evolution, and offer insight into likely schemes for studying dark energy at higher redshifts.

Past weeks:
page by Neill Reid, updated 2/9/2006