This week on HST


HST Programs: March 16 - March 22, 2015

Program Number Principal Investigator Program Title
13498 Jennifer Lotz, Space Telescope Science Institute HST Frontier Fields - Observations of MACSJ0717.5+3745
13641 Peter Capak, California Institute of Technology A Detailed Dynamical And Morphological Study Of 5
13646 Ryan Foley, University of Illinois at Urbana - Champaign Understanding the Progenitor Systems, Explosion Mechanisms, and Cosmological Utility of Type Ia Supernovae
13650 Kevin France, University of Colorado at Boulder The MUSCLES Treasury Survey: Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems
13652 Boris T. Gaensicke, The University of Warwick The frequency and chemical composition of rocky planetary debris around young white dwarfs: Plugging the last gaps
13657 Jeyhan Kartaltepe, National Optical Astronomy Observatory, AURA Probing the Most Luminous Galaxies in the Universe at the Peak of Galaxy Assembly
13669 Marcella Carollo, Eidgenossiche Technische Hochschule (ETH) The star-formation histories within clumpy disks at z ~ 2.2
13677 Saul Perlmutter, University of California - Berkeley See Change: Testing time-varying dark energy with z>1 supernovae and their massive cluster hosts
13679 Lorenz Roth, Royal Institute of Technology Europa's Water Vapor Plumes: Systematically Constraining their Abundance and Variability
13695 Benne W. Holwerda, Sterrewacht Leiden STarlight Absorption Reduction through a Survey of Multiple Occulting Galaxies (STARSMOG)
13709 Adam Michael Ritchey, University of Washington Constraining the Cosmic-ray Acceleration and Gamma-ray Emission Processes in IC 443
13728 Steven Kraemer, Catholic University of America Do QSO2s have Narrow Line Region Outflows? Implications for quasar-mode feedback
13755 Jenny E. Greene, Princeton University The Hosts of Megamaser Disk Galaxies (II)
13767 Michele Trenti, University of Cambridge Bright Galaxies at Hubble's Detection Frontier: The redshift z~9-10 BoRG pure-parallel survey
13773 Rupali Chandar, University of Toledo H-alpha LEGUS: Unveiling the Interplay Between Stars, Star Clusters, and Ionized Gas
13817 Thomas M. Brown, Space Telescope Science Institute A Direct Distance to an Ancient Metal-Poor Star Cluster
13825 Justyn Maund, The Queen's University of Belfast Stellar Forensics VI: A post-explosion view of the progenitor of SN 2012aw
13834 Roeland P. van der Marel, Space Telescope Science Institute The Proper Motion Field along the Magellanic Bridge: a New Probe of the LMC-SMC interaction
13846 Todd Tripp, University of Massachusetts - Amherst The COS Absorption Survey of Baryon Harbors (CASBaH): Probing the Circumgalactic Media of Galaxies from z = 0 to z = 1.5
13862 Timothy M. Heckman, The Johns Hopkins University Measuring the Impact of Starbursts on the Circum-Galactic Medium
13866 David Jewitt, University of California - Los Angeles Determining the Nature and Origin of Mass Loss from Active Asteroid P/2013 P5
13868 Dale D. Kocevski, Colby College Are Compton-Thick AGN the Missing Link Between Mergers and Black Hole Growth?
13943 Amy E. Reines, University of Michigan Probing the Growth of Massive Black Holes in Dwarf Galaxies with Chandra and HST

Selected highlights

GO 13652: The frequency and chemical composition of rocky planetary debris around young white dwarfs: Plugging the last gaps


Artist's impression of a comet spiralling in to the white dwarf variable, G29-38
During the 1980s, one of the techniques used to search for brown dwarfs was to obtain near-infrared photometry of white dwarf stars. Pioneered by Ron Probst (KPNO), the idea rests on the fact that while white dwarfs are hot (5,000 to 15,000K for the typcail targets0, they are also small (Earth-sized), so they have low luminosities; consequently, a low-mass companion should be detected as excess flux at near- and mid-infrared wavelengths. In 1988, Ben Zuckerman and Eric Becklin detected just this kind of excess around G29-38, a relatively hot DA white dwarf that also happens to lie on the WD instability strip. However, follow-up observations showed that the excess peaked at longer wavelengths than would be expected for a white dwarf; rather, G 29-38 is surrounded by a dusty disk. Given the orbital lifetimes, those dust particles must be regularly replenished, presumably from rocky remnants of a solar system. G 29-38 stood as a lone prototype for almost 2 decades, until a handful of other dusty white dwarfs were identified from Spitzer observations within the last couple of years.In subsequent years, a significant number of DA white dwarfs have been found to exhibit narrow metallic absorption lines in their spectra. Those lines are generally attributed to "pollution" of the white dwarf atmospheres. Given that the diffusion time for metals within the atmospheres is short (tens to hundreds of years), the only reasonable means of maintaining such lines in ~20% of the DA population is to envisage continuous accretion from a surrounding debris disk. The Cosmic Origins Spectrograph (COS) is an ideal instrument for probing the abundance of trace elements in white dwarfs atmospheres: more than 70 systems have been observed, with detection rates running at around 50%. The presentSNAPSHOT program aims to cap pervious investigations by targeting white dwarfs with cooling ages of 5-25 Myrs and 100-300 Myrs: models suggest that planetary collisions should be frequent at the younger ages, when the parent stars have just completed extensive mass loss on the AGB.

GO 13767: Bright Galaxies at Hubble's Detection Frontier: The redshift z~9-10 BoRG pure-parallel survey


The ACS optical/far-red image of the Hubble Ultra Deep Field
Galaxy evolution in the early Universe is a discipline of astronomy that has been transformed by observations with the Hubble Space Telescope. The original Hubble Deep Field, the product of 10 days observation in December 1995 of a single pointing of Wide Field Planetary Camera 2, demonstrated conclusively that galaxy formation was a far from passive process. The images revealed numerous blue disturbed and irregular systems, characteristic of star formation in galaxy collisions and mergers. Building on this initial progam, the Hubble Deep Field South (HDFS) provided matching data for a second southern field, allowing a first assessment of likely effects due to field to field cosmic variance, and the Hubble Ultra-Deep Field (UDF) probed to even fainter magitude with the Advanced Camera for Surveys (ACS). The highest redshift objects found in the UDF have redshifts approaching z~7. Pushing to larger distances, and greater ages, demands observatons at near-infrared wavelengths, as the characteristics signatures of star formation are driven further redward in the spectrum. Wide Field Camera 3, installed in Servicing Mission 4, is well suited to these observations, and a number of programs are in place in Cycle 17 that address these issues. Indeed, WFC3 is employed in pure parallel mode by several programs. These take advantage of other science programs, usually with COS, that involve 2-5 orbit pointings on sources at high galactic latitude. The WFC3 pointing is unplanned, since it depends on the orientation adopted for the prime observations, but 2-5 orbits of IR imaging can reach galaxies at redshifts exceeding z=7 (potentially even z~8) in high latitude fields. The present program builds on similar programs in Cycles 17 and 19, and aims to detect the brightest galaxies at z~9, within 600 Myrs of the Big Bang.

GO 13773: H-alpha LEGUS: Unveiling the Interplay Between Stars, Star Clusters, and Ionized Gas


UGC 4305 = Holmberg II - Arp 268, one of the star-forming galaxies targeted by LEGUS
Understanding the global architecture of star formation is a key step towards understanding the morphological evolution of galaxies and the characteristics of the underlying stellar populations. HST has devoted extensive resources to observations of nearby galaxies over its lifetime, including detailed surveys of a handful of systems, notably the PHAT survey of M31, with the enhanced imaging capabilities made available following SM4. Most programs, however, have focused on optical, far-red and, to a lesser extent, near-infrared wavelengths. While those observations provide high-quality colour-magnitude data that enable an exploration of relatively mature populations, they are less effective at probing active star-formation sites populated by young, high-mass stars. Those regions are most prominent at ultraviolet wavelengths. The HST LEGUS capitalises on the past heritage of HST observations by adding near-UV imaging for 50 nearby galaxies, drawn from a catalogue of 400 systems within ~11 Mpc of the Milky Way. They have been selected to provide a fair sampling of the wide variety of galactic systems within that volume. LEGUS itself is imaging star-forming regions at near-UV and blue wavelengths using the WFC3 UVIS channel with the F275W, F336W and F438W filters, supplemented by F55W and F814W (V and I) where necessary. The present program builds on that foundation by adding WFC3 narrow-band (F657N) H-alpha imaging of 32 galaxies from the sample.

GO 13834: The Proper Motion Field along the Magellanic Bridge: a New Probe of the LMC-SMC interaction


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. Understanding the full scope of the interactions demands knowledge of the tangential motions of these systems - that is, proper motion measurements. Given the distances of the Clouds (~50 kpc.), the actual motions amount to only a few milliarcseconds, but the high spatial resolution and high stability of HST imaging makes such measurements possible. Past observing programs (eg GO 11730) have concentrated on the LMC, using the now-defunct ACS High Resolution Camera (ACS/HRC), the Planetary Camera on WFPC2 and the UVIS camera on WFC3 to target known QSOs lying behind the Clouds; the QSOs serve as fixed reference points for absolute astrometry of the numerous foreground LMC/SMC stars. A recent Cycle 21 program focused on the SMC, targeting 30 newly identified background QSos for WFC3 observations over a two-year period. The present program expands observations to several fields along the Magellanic bridge, a complex of gas and stars that conencts the two clouds, and will test the hypothsesis that the clouds are undergoing their first interaction with teh Milky Way.

Past weeks:
page by Neill Reid, updated 11/11/2014
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