This week on HST

HST Programs: December 24 - December 30, 2007

Program Number Principal Investigator Program Title Links
10787 Jane Charlton, The Pennsylvania State University Modes of Star Formation and Nuclear Activity in an Early Universe Laboratory Abstract
10812 Slawomir Piatek, New Jersey Institute of Technology Space Motions for the Draco and Sextans Dwarf Spheroidal Galaxies Abstract
10854 Karl Stapelfeldt, Jet Propulsion Laboratory Coronagraphic Imaging of Bright New Spitzer Debris Disks II Abstract
10873 Mark Whittle, The University of Virginia The Radio-quiet Jet Flow in Markarian 34 Abstract
10889 Roelof de Jong, Space Telescope Science Institute The Nature of the Halos and Thick Disks of Spiral Galaxies Abstract
10921 C. O'Dell, Vanderbilt University Tangential Velocities of Objects in the Orion Nebula and Locating the Embedded Outflow Sources Abstract
11083 Patrick Cote, Dominion Astrophysical Observatory The Structure, Formation and Evolution of Galactic Cores and Nuclei Abstract
11103 Harald Ebeling, University of Hawaii A Snapshot Survey of The Most Massive Clusters of Galaxies Abstract
11107 Timothy M. Heckman, The Johns Hopkins University Imaging of Local Lyman Break Galaxy Analogs: New Clues to Galaxy Formation in the Early Universe Abstract
11124 David V. Bowen, Princeton University The Origin of QSO Absorption Lines from QSOs Abstract
11130 Luis Ho, Carnegie Institution of Washington AGNs with Intermediate-mass Black Holes: Testing the Black Hole-Bulge Paradigm, Part II Abstract
11134 Karen Knierman, University of Arizona WFPC2 Tidal Tail Survey: Probing Star Cluster Formation on the Edge Abstract
11145 Nuria Calvet, University of Michigan Probing the Planet Forming Region of T Tauri Stars in Chamaeleon Abstract
11165 Joshua Winn, Massachusetts Institute of Technology The Radius of the Super-Neptune HD 149026b Abstract
11178 William M. Grundy, Lowell Observatory Probing Solar System History with Orbits, Masses, and Colors of Transneptunian Binaries Abstract
11195 Arjun Dey, National Optical Astronomy Observatories Morphologies of the Most Extreme High-Redshift Mid-IR-luminous Galaxies II: The `Bump' Sources Abstract
11201 Nitya Kallivayalil, Harvard University Systemic and Internal motions of the Magellanic Clouds: Third Epoch Images Abstract
11202 Leon Koopmans, Kapteyn Astronomical Institute The Structure of Early-type Galaxies: 0.1-100 Effective Radii Abstract
11210 George Fritz Benedict, University of Texas at Austin The Architecture of Exoplanetary Systems Abstract
11211 George Fritz Benedict, University of Texas at Austin An Astrometric Calibration of Population II Distance Indicators Abstract
11216 John A. Biretta, Space Telescope Science Institute HST / Chandra Monitoring of a Dramatic Flare in the M87 Jet Abstract
11218 Howard Bond, Space Telescope Science Institute Snapshot Survey for Planetary Nebulae in Globular Clusters of the Local Group Abstract
11220 Jeff Cooke, University of California - Irvine Direct Detection and Mapping of Star Forming Regions in Nearby, Luminous Quasars Abstract
11309 Jacob L. Bean, University of Texas at Austin Chemical Composition of an Exo-Neptune Abstract
11339 Andreas Zezas, Smithsonian Institution Astrophysical Observatory A deep observation of NGC4261: understanding its unique X-ray source population, gas morphology, and jet properties Abstract

Some selected highlights

GO 10889: The Nature of the Halos and Thick Disks of Spiral Galaxies

Ground-based imaging of the edge-on spiral, NGC 891 The stars in the Milky Way are generally grouped into stellar populations, building blocks that provide insight into the process of galaxy assembly. The traditional populations are the near-spherical, metal-poor Halo, representing the first significant burst of star formation; the Disk, whose constituents have higher metallicities, a flattened density distribution (which defines the Galactic Plane) and significant angular momentum, suggesting a formation history that includes collapse and dissipation; and the central Bulge, which, with a spheroidal distribution and broad metallicity range, may be something of an amalgam of disk and halo. The original models for the Disk envisaged a relatively simple population, with a continuous star formation history and an exponential density distribution, both radially and perpendicular to the Plane. However, in the mid-1980s, starcount analyses revealed more complexity in the vertical density distribution, with evidence for two components with scaleheights ~300 and 1000-1300 pc. Subsequent investigations of the more extended component, dubbed the thick disk, suggest that it probably formed as a result of a merger with a massive satellite early in the Milky Way's history (8-10 Gyrs ago). Ground-based observations suggest that some other spiral galaxies possess a similar component. Clearly, the frequency of such systems and their age distribution offer clues to the merging history of the average spiral galaxy. The present program will use ACS, WFPC2 and NICMOS to image seven edge-on spirals at several locations perpendicular to the Plane, with the aim of resolving the underlying stellar populations and tracing the metallicity distribution and overall morphology of the extended disk components.

GO 11083: The Structure, Formation and Evolution of Galactic Cores and Nuclei

A wide-field view of the Virgo cluster The Virgo cluster, lying at a distance of ~20 MPc, is the nearest large galaxy cluster. The cluster embraces more than 2,000 galaxies, with masses ranging from ~3 x1012 MSun for the central giant elliptical, M87, to ~109 MSun dwarf systems, predominantly ellipticals but with a smattering of irregulars. In Cycle 11, the same proposal used the Advanced Camera for Surveys to observe more than 100 elliptical and S0 galaxies in Virgo, obtaining deep images in the SDSS g (green) and z (far-red) passbands. These observations show a systematic variation with luminosity in the surfacve brightness profile. Giant ellipticals have a relatively flat brightness profile in the central regions, while dwarfs tends to have compact nuclei. The aim of the current proposal is to use ultraviolet (WFPC2/F225W) and near-infrared (NIC1/F160W) images of the central regions to probe star formation and the star formation history on scales of 0.1-1.0 arcsecond (10-100 parsecs).

GO 11201: Systemic and Internal motions of the Magellanic Clouds: Third Epoch Images

The Large Magellanic Cloud (upper left) with the Small Magellanic Cloud (right) and the (foreground) Galactic globular cluster47 Tucanae The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are the most massive satellites of the Milky Way galaxy. The orbital motions of these systems can be used to probe the mass distribution of Milky Way, and backtracking the orbits can shed light on how the three systems have interacted, In particular, the well known Magellanic Stream, stretching between the two Clouds, is thought to be a product either of interactions between the Clouds, or of ram-stripping of gas from the LMC on its last passage through the Plane of the Milky Way. The present program builds on observations obtained at two epochs with the now-defunct (but perhaps soon to be revived) ACS High Resolution Camera (ACS/HRC). The previous programs targeted known QSOs lying behind the Clouds; the QSOs serve as fixed reference points for absolute astrometry of the numerous foreground LMC/SMC stars. First epoch observations were made in late 2002 (GO 9462), with the follow-up imaging in late 2004 (GO 10130). The tangential motions of the Clouds amount to only a few milliarcseconds, but the high spatial resolution and high stability of HST imaging makes such measurements possible, even with only a 2-year baseline. Surprisingly, the initial results suggest that the 3-D motions of both clouds are much higher than expected, suggesting either that the LMC/SMC/MW is either dynamically very young, or unbound. The present program will use WFPC2 to obtain third-epoch data in the same fields, providjng a crucial test of the initial results

GO 11210: The Architecture of Exoplanetary Systems

Artist's impression of a young planetary system Immanuel Kant is generally credited with first proposing that the planets in the Solar System coalesced from a flat, rotating disk formed by the Solar Nebula. Direct confirmation of that process only came in the early 1990s, when millimetre-wave interferometers were able to detect molecular gas in Keplerian rotation around a handful of nearby young stars. Since then, there have been numerous other observations, including Hubble's images of proplyds (protoplanetary disks) in the Orion Cluster, and Hubble and Spitzer observations of edge-on disks in other young stars. One of the clear selling points of the Solar Nebula disk model is that it appears to offer a natural path to forming planets with coplanar orbits, matching (most of) our observations of the Solar System. On the other hand, as our knowledge of exoplanetary systems has accumulated over the last decade, it has become clear that dynamical interactions may play a very important role in the evolution of these systems. In particular, disk/planet interactions are generally regarded as responsible for the inward migration of gas giants to form hot Jupiters in <3 day period orbits. Planet-planet interactions could lead to significant changes in orbital inclination. Radial velocity planet searches are uncovering more and more multi-planet systems. This program focuses the high precision of HST's astrometric detectors, the Fine Guidance Sensors, on four of those systems. The aim is to complement the existing radial velocity measurements with sub-milliarcsecond precision astrometry, allowing determination of the true orbital paths - specifically, the relative inclination - of the low-mass objects in these systems.

Past weeks:
page by Neill Reid, updated 24/12/2007