This week on HST


HST Programs: March 12 - March 18, 2007

Program Number Principal Investigator Program Title Links
10610 George Benedict, University of Texas at Austin Astrometric Masses of Extrasolar Planets and Brown Dwarfs Abstract
10798 Leon Koopmans, Kapteyn Astronomical Institute Dark Halos and Substructure from Arcs & Einstein Rings Abstract
10801 Keith Noll, Space Telescope Science Institute Direct Determination of Kuiper Belt Object Diameters with HST Abstract
10802 Adam Riess, Space Telescope Science Institute SHOES-Supernovae, HO, for the Equation of State of Dark energy Abstract
10808 Pieter van Dokkum, Yale University Morphologies of spectroscopically-confirmed red and dead galaxies at z~2.5 Abstract
10815 Tom Brown, Space Telescope Science Institute The Blue Hook Populations of Massive Globular Clusters Abstract
10836 S. Stanford, University of California - Davis The Red Sequence at 1.3 < z < 1.4 in Galaxy Clusters Abstract
10862 John Clarke, Boston University Comprehensive Auroral Imaging of Jupiter and Saturn during the International Heliophysical Year Abstract
10890 Arjun Dey, NOAO Morphologies of the Most Extreme High-Redshift Mid-IR-Luminous Galaxies Abstract
10906 Sylvain Veilleux, University of Maryland The Fundamental Plane of Massive Gas-Rich Mergers: II. The QUEST QSOs Abstract
10907 Scott Anderson, University of Washington New Sightlines for the Study of Intergalactic Helium: A Dozen High-Confidence, UV-Bright Quasars from SDSS/GALEX Abstract
10918 Wendy Freedman, Carnegie Institution of Washington Reducing Systematic Errors on the Hubble Constant: Metallicity Calibration of the Cepheid PL Relation Abstract
10927 Wei-Chun Jao, Georgia State University Research Foundation The Weight-Watcher Program for Subdwarfs Abstract
10989 George Benedict, University of Texas at Austin Astrometric Masses of Extrasolar Planets and Brown Dwarfs Abstract
10999 Carolyn Brinkworth, Jet Propulsion Laboratory Testing the first direct measurement of cataclysmic variable evolution Abstract
11080 Daniela Calzetti, University of Massachusetts Exploring the Scaling Laws of Star Formation Abstract
11084 Dan Zucker, Institute of Astronomy, Cambridge Probing the Least Luminous Galaxies in the Local Universe Abstract
11085 Bill Sparks, Space Telescope Science Institute Europa in Eclipse: Tenuous Atmosphere, Electromagnetic Activity and Surface Luminescence Abstract
11098 Andrew Levan, University of Hertfordshire Pinning down the redshift of the J-band dropout JD0910+46 Abstract

Some selected highlights

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 is being 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 was used in parallel to search for high-redshift supernovae. While the ACS observations are no longer possible, NICMOS monitoring of the Cepheids continues.

GO 10862: Comprehensive Auroral Imaging of Jupiter and Saturn during the International Heliophysical Year

Hubble ultraviolet image of auroral activity near Jupiter's north magnetic pole 2007 has been designated the International Heliophysical Year, and HST will be playing a key part in the associated scientific activities by participating in a detailed investigation of auroral activity in jupiter and Saturn. Planetary aurorae are stimulated by the influx of charged particles from the Sun, which travel along magnetic field lines and funnel into the atmosphere near the magnetic poles. Aurorae therefore require that a planet has both a substantial atmosphere and a magnetic field. They are a common phenomenon on Earth, sometimes visible at magnetic latitudes more than 40 degrees from the pole, and have also been seen on Jupiter, Saturn, Uranus and Neptune. Jovian auroral activity is also affected by the Galilean satellites, which generate electric currents that can produce bright auroral spots (see figure), and, in some cases, have their own auroral storms. HST is using the ACS Solar Blind Channel to monitor activity on the two largest gas giants. The initial campaign, starting in early January, focused on Saturn while it was at opposition. In February, the New Horizons spacecraft flew by Jupiter, with closest approach on February 28th, and used the strong gravitational field to propel it on its way to Pluto. During the fly-by, New Horizons is carrying out a number of experiments ( see this link ) while HST monitors the large-scale behaviour. Finally, Jupiter will be surveyed while it is at opposition in June 2007.

GO 10918: Reducing Systematic Errors on the Hubble Constant: Metallicity Calibration of the Cepheid PL Relation

M101, the spiral galaxy targetted in this program 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. However, the Cepheid period-Luminosity relation has long been suspected of being dependent on metallicity. The LMC Cepheids have a lower average metallicity than both the Galactic Cepheids that define the local calibration and the Cepheids in more distant galaxies used to derive H0 - setting the stage for potential systematic errors in the distance scale. The present program aims to address this issue through HST ACS (and, more recently, HST WFPC2) imaging of Cepheids in several fields in the relatively nearby spiral galaxy, M101. The M101 disk has a metallicity gradient, and the targeted fields have been chosen to sample a range of metallicities. Comparison of the perid-luminosity relations from the separate fields will allow direct measurement of any systematic metallicity-based variations.

Past weeks:
page by Neill Reid, updated 28/1/2007