This week on HST


HST Programs: May 26 - June 1, 2014

Program Number Principal Investigator Program Title
13117 Andrew J. Levan, The University of Warwick A Chandra/HST survey of dark gamma-ray bursts and their hosts
13288 Amy Kathryn Furniss, Stanford University PG 1424+240: Too Distant to be Seen?
13297 Giampaolo Piotto, Universita degli Studi di Padova The HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation
13305 Carolin Villforth, University of St. Andrews Do mergers matter? Testing AGN triggering mechanisms from Seyferts to Quasars
13313 Mederic Boquien, University of Cambridge Determining attenuation laws down to the Lyman break in z~0.3 galaxies
13315 Marc W. Buie, Southwest Research Institute Pluto Satellite Orbits in Support of New Horizons
13319 Alexandros Gianninas, The University of Oklahoma COS Spectroscopy of Pulsating, Metal-Rich, Extremely Low Mass White Dwarfs
13327 Eileen T Meyer, Space Telescope Science Institute Proper Motions at 500 Mpc: Measuring Superluminal motions in Optical Jets with HST
13330 Bradley M Peterson, The Ohio State University Mapping the AGN Broad Line Region by Reverberation
13335 Adam Riess, The Johns Hopkins University HST and Gaia, Light and Distance
13352 Matthew A. Malkan, University of California - Los Angeles WFC3 Infrared Spectroscopic Parallel Survey WISP: A Survey of Star Formation Across Cosmic Time
13366 Roelof S. de Jong, Leibniz-Institut fur Astrophysik Potsdam (AIP) The vertical disk structure of spiral galaxies and the origin of their thick disks
13383 Mary E. Putman, Columbia University in the City of New York Measuring the Properties of Dwarf Streams
13393 Dennis Zaritsky, University of Arizona Galaxy Transformation in the Infall Regions of Clusters
13410 Cristina Pallanca, Universita di Bologna COSMIC-LAB: a BSS orbiting a NS? The companion to the supermassive NS in NGC6440.
13421 Madelon C.P. Bours, The University of Warwick CSS 41177: an eclipsing double white dwarf binary
13429 Margherita Giustini, European Space Agency - ESTEC Unveiling the X-ray/UV Connection in AGN Winds: the PG 1126-041 Case Study
13437 Jane R. Rigby, NASA Goddard Space Flight Center The Morphology and Star Formation Distribution in a Big Cool Spiral LIRG
13452 Matthew Hayes, Stockholm University Coupling the emission of ionizing radiation and Lyman alpha
13459 Tommaso L. Treu, University of California - Santa Barbara The Grism Lens-Amplified Survey from Space {GLASS}
13473 Timothy M. Heckman, The Johns Hopkins University On the Nature of Highly Ionized Gas in the Halos of Normal Star-Forming Galaxies
13482 Britt Lundgren, University of Wisconsin - Madison The Evolving Gas Content of Galaxy Halos: A Complete Census of MgII Absorption Line Host Galaxies at 0.7 < z < 2.5
13487 Michael Salz, Universitat Hamburg, Hamburger Sternwarte A pilot study to characterize the Lyman alpha emission of active exoplanet host stars
13495 Jennifer Lotz, Space Telescope Science Institute HST Frontier Fields - Observations of Abell 2744
13613 C. S. Kochanek, The Ohio State University Dust to Dust: Monitoring the Evolution of the New Class of Self-Obscured Transients
13629 Yael Naze, Universite de Liege Characterizing the high-energy properties of a highly magnetized star
13632 John T. Clarke, Boston University Seasonal Dependence of the Escape of Martian Water

Selected highlights

GO 13297: The HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation


Hubble image of the metal-poor globular cluster, M15
Globular clusters are members of the Galactic halo population, representing remnants from the first extensive period of star formation in the Milky Way. As such, the properties of the 106 to 107 stellar constituents can provide crucial insight into the earliest stages of galaxy formation. Until recently, conventional wisdom was that these are simple systems, where all the stars formed in a single starburst and, as a consequence, have the same age and metallicity. One of the most surprising disoveries in recent years is the realisation that this simple picture no longer holds. Up until about 5 years ago, the only known counter-example to convention was the cluster Omega Centauri, which is significantly more massive than most clusters and has both a complex main sequence structure and a range of metallicities among the evolved stars. High precision photometric observations with HST has demonstrated that Omega Cen is far from unique, with multiple populations evident in numerous other clusters, including NGC 2808, NGC 1851, 47 Tuc and NGC 6752. Multiple populations have also been discerned in a number of clusters in the Magellanic clouds. Sustaining multiple bursts of star formation within these systems demands that they retain gas beyond the first star forming event, which appears to set a requirement that these clusters were significantly more massive during their epoch of formation; put another way, the current globulars may represent the remnant cores of dwarf galaxy-like systems. That, in turn, implies that the stars ejected from those systems make a significant contribution to the current galactic halo. One of the most effective means of identifying and studying multi-population clusters is combining high-precision photometry over a wide wavelength range, particularly extending to UV wavelengths. Sixty-five globular clusters already have R/I (F606W, F814W) Hubble imaging and photometry thanks to the Cycle 14 program, An ACS Survey of Galactic Globular Clusters (GO 10775). The present program aims to build on those data by adding UV/blue observations using the F275W, F336W and F438W filters on the WFC3-UVIS camera. The colorus derived from these filters enable characterisation of the C, N and O abundances of the component stellar populations in these systems.

GO 13305: Do mergers matter? Testing AGN triggering mechanisms from Seyferts to Quasars


Composite optical/radio image of CenA, the elltipical merger that harbours the nearest AGN
Quasars are highly energetic sources that can achieve luminosities substantially exceeding 1012 LSun. These objects are generally believed to be powered by accretion onto a central supermassive black hole, with M > 107 MSun. Many QSOs reside within galaxies that are morphologically similar to elliptical galaxies, predominantly gas poor at the present epoch. This raises the issue of how one fuels the central, active black hole. One possibility is through mergers, with the QSO host assimilating smaller, gas-rich neighbours. Many nearby ellipticals are known to exhibit characteristics signatures of mergers - tidal tails, dust lanes and shells. Cen A is the classic example, which also happens to support a weak AGN and mild star formation within the dust lane. This proposal builds on previous HST observations of AGN at moderately low redshift (0.5 < z , 0.7) within the Chandra Deep Field South (CDFS). Those data showed little evidence for the disturbed morphology normally associated with mergers; however, the target galaxies were all of relatievly low instrinsic luminosity. The present program extends observations to higher luminosity QSOs, testing the hypothesis of a causal connection between mergers and AGN activity.

GO 13315: Pluto Satellite Orbits in Support of New Horizons


Hubble Space Telescope images of the Pluto system, including the recently discovered moons, P4 and P5
Pluto, one of the largest members of the Kuiper Belt and, until recently, the outermost planet in the solar system, has been in the news over the last year or two. Besides the extended "planet"/"dwarf planet" debate, Pluto is the primary target of the New Horizons Mission. In 1978, James Christy discovered from analyses of photographic plates that Pluto has a relatively large companion moon, Charon, with a diameter of ~1200 km, or almost half that of Pluto itself. In 2005, Hubble observations led to the discovery of two small moons, christened Nix and Hydra. These two new moons are 5,000 fainter than Pluto itself, implying diameters as small as ~30-50 km if the surface composition is similar to Pluto itself. Over the past two years, a series of observations were taken in support of the New Horizons mission, using WFC3 to search for faint rings due to dust particles that might jeopardise the space craft and require a course correction. While no rings were detected unequivocally, two small satellite, christened "P4" and "P5", have been discovered. Both are significantly fainter than Nix and Hydra, and may well be as small as 10-13 km in size. There is also some evidence that might point to the presence of a debris ring within Charon's orbit. The present observations, again in support of New Horizons, will use WFC3 to push to fainter magnitudes to both better characterise the P4 and P5 orbits and search for even fainter moons.

GO 13319: COS Spectroscopy of Pulsating, Metal-Rich, Extremely Low Mass White Dwarfs


The surface-temperature map on a pulsating white dwarf (Figure by Mike Montgomery U. Texas group)
White dwarfs are compact, electron-degenerate remnants that represent the final evolutionary stage for stars less massive than ~7 Msun. White dwarfs emerge from planetary nebulae with extremely high surface temperatures, but with no central energy source, they simply cool like a brick. As they cool, the spectral energy distribution and the spectral characteristics evolve with time. Most white dwarfs have thin hydrogen envelopes, and are therefore have strong Balmer-series absorption lines in the optical at temperatures above ~8,000 degrees (DA white dwarfs), although a sizeable minority have helium envelopes and spectra dominated by helium lnes (DB white dwarfs). In most cases, the mass of the white dwarf scales with the mass of the progenitor, with typical masses around 0.6 MSun for 1-2 solar mass progenitors. A small number of white dwarfs, however, have much lower masases, closer to ~0.2 MSun. These extremely low-mass (ELM) white dwarfs are generally believed to have formed through binary evolution, with the envelope of the progenitor stripped through mass loss and companion accretion during the red giant phase, truncating evolution before the core could complete its growth. The present program aims to obtain COS UV spectra of two ELM white dwarfs, and has two goals in mind: first, some mdoels sugegst that these ELM white dwarfs are extremely metal-rich, and the COS observations will enable direct measurement of the atmospheric metallicity and determination whether these abundances are intrinsic or due to dust accretion; and, second, time-tag measurements with COS can be used to determine whether the degenerates are p-mode pulsators.

Past weeks:
page by Neill Reid, updated 27/5/2014
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