This week on HST


HST Programs: August 31 - September 6, 2009


Program Number Principal Investigator Program Title Links
11235 Jason A. Surace, California Institute of Technology HST NICMOS Survey of the Nuclear Regions of Luminous Infrared Galaxies in the Local Universe Abstract
11563 Garth Illingworth, University of California, Santa Cruz Galaxies at z~7-10 in the Reionization Epoch: Luminosity Functions to <0.2L* from Deep IR Imaging of the HUDF and HUDF05 Fields Abstract
11584 Kristin Chiboucas, University of Hawaii Resolving the Smallest Galaxies with ACS Abstract
11594 John M. O'Meara, Saint Michaels College A WFC3 Grism Survey for Lyman limit absorption at z=2 Abstract
11644 Michael E. Brown, California Institute of Technology A dynamical-compositional survey of the Kuiper belt: a new window into the formation of the outer solar system Abstract
11649 Jean-Claude M. Gerard, Universite de Liege Elucidating the mystery of the Io footprint time variations Abstract
11650 William M. Grundy, Lowell Observatory Mutual Orbits, Colors, Masses, and Bulk Densities of 3 Cold Classical Transneptunian Binaries Abstract
11657 Letizia Stanghellini, National Optical Astronomy Observatories The population of compact planetary nebulae in the Galactic Disk Abstract
11690 Brian R. Espey, University of Dublin, Trinity College EG And: Providing the Missing Link Required for Modelling Red Giant Mass-loss Abstract
11706 Peter McCullough, Space Telscope Science Institute The Parallax of the Planet Host Star XO-3 Abstract
11714 Howard E. Bond, Space Telescope Science Institute Snapshot Survey for Planetary Nebulae in Local Group Globular Clusters Abstract
11721 Richard S. Ellis, California Institute of Technology Verifying the Utility of Type Ia Supernovae as Cosmological Probes: Evolution and Dispersion in the Ultraviolet Spectra Abstract
11788 George Fritz Benedict, University of Texas at Austin The Architecture of Exoplanetary Systems Abstract
11789 George Fritz Benedict, University of Texas at Austin An Astrometric Calibration of Population II Distance Indicators Abstract
11790 John Wisniewski, NASA Goddard Space Flight Center HST/FGS Astrometric Search for Young Planets Around Beta Pic and AU Mic Abstract

Selected highlights

GO 11235: HST NICMOS Survey of the Nuclear Regions of Luminous Infrared Galaxies in the Local Universe

A NICMOS image of the interacting LIRG, NGC 6090 Luminous infrared galaxies (LIRGs) have total luminosities that exceed 1011.4 LSun, with most of the energy emitted at wavelengths longward of 10 microns. Many (perhaps most) of these galaxies are interacting or merging disk galaxies, with the excess infrared luminosity generated by warm dust associated with the extensive star formation regions. Many systems also exhibit an active nucleus, and may be in the process of evolving towards an S0 or elliptical merger remnant. This program builds on a previous ACS survey of 88 systems from the IRAS Revised Bright Galaxy Sample (GO 10592) in the F439W and F814W passbands. In Cycle 16, Program GO 11196 used the ACS/SBC and WFC3 to obtain far- (F140LP) and near- (F218W) UV imaging of 27 galaxies; GO 11235 concentrates on near-infrared H-band WFC3 imaging of the galaxy cores. Combined with the previously obtained B- and I-band data, these observations will probe
  • the distribution of star formation activity and the presence of bars and bridges, funneling gas towards active regions
  • the age distribution of star clusters
  • the relationship between star formation and AGN activity
  • correlations between near-infrared emission and the mid-IR structures identified from Spitzer IRAC imaging;
  • the presence of coherent structure, bars or bridges, that might funnel gas into the nuclei;
  • the overall structural properties of the LIRGS as a function of luminosity and environment
The observations will also provide a detailed UV images for a reference sample of nearby galaxies. Observations of several interacting system are scheduled for this week.

GO 11650: Orbits, Masses, and Densities of Three Cold Classical Transneptunian Binaries

Preliminary orbital determination for the KBO WW31, based on C. Veillet's analysis of CFHT observations; the linked image shows the improved orbital derivation, following the addition of HST imaging The Kuiper Belt consists of icy planetoids that orbit the Sun within a broad band stretching from Neptune's orbit (~30 AU) to distance sof ~50 AU from the Sun (see David Jewitt's Kuiper Belt page for details). Over 500 KBOs (or trans-Neptunian objects, TNOs) are currently known out of a population of perhaps 70,000 objects with diameters exceeding 100 km. Approximately 2% of the known KBOs are binary (including Pluto, one of the largest known KBOs, regardless of whether one considers it a planet or not). This is a surprisingly high fraction, given the difficulties involved in forming such systems and the relative ease with which they can be disrupted. It remains unclear whether these systems formed from single KBOs (through collisions or 3-body interactions) as the Kuiper Belt and the Solar System have evolved, or whether they represent the final tail of an initial (much larger) population of primordial binaries. These issues can be addressed, at least in part, through deriving a better understanding of the composition of KBOs - and those properties can be deduced by measuring the orbital parameters for binary systems. The present proposal aims to use HST WFC3 observations to map the orbits of three binary systems. Those observations will be ued to determine the orbital period and semi-major axis and the total system mass, while the mid-infrared properties (measured by Spitzer) allow an assessment of the surface area/diameters; combining these measurements gives an estimate of the mean density.

GO 11721: Verifying the Utility of Type Ia Supernovae as Cosmological Probes: Evolution and Dispersion in the Ultraviolet Spectra

A recent supernova in M100 Supernovae are the most spectacular form of stellar obituary. In recent years, these celestial explosions have acquired even more significance through the use of Type Ia supernovae as distance indicators in mapping the `dark energy' acceleration term of cosmic expansion. However, while there is a well-established model for the two main types of supernovae, runaway fusion on the surface of a white dwarf in a binary system, there are still some uncertainties as to the uniformity of the events, and the consequence potential for systematic uncertainties in the distance estimates. One of the questionmarks comes from spectroscopy of a number of supernovae at intermediate redshift (z~0.5) that appears to show a substantial dispersion in properties at UV wavelengths. The present program aims to probe this issue by using STIS to obtain UV spectra of nearby supernovae, and therefore examining the detailed behaviour in the local universe.

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).

Past weeks:
page by Neill Reid, updated 23/9/2009