This week on HST

HST Programs: October 7 - October 13, 2013

Program Number Principal Investigator Program Title
12109 Julianne Dalcanton, University of Washington A Panchromatic Hubble Andromeda Treasury - I
12588 Kailash C. Sahu, Space Telescope Science Institute Accurate Mass Determination of the Old White Dwarf G105-30 through Astrometric Microlensing
12880 Adam Riess, The Johns Hopkins University The Hubble Constant: Completing HST's Legacy with WFC3
12903 Luis C. Ho, Carnegie Institution of Washington The Evolutionary Link Between Type 2 and Type 1 Quasars
12943 Yujin Yang, Max-Planck-Institut fur Astronomie, Heidelberg Testing the Cold Stream Accretion Model Using Lyman Alpha Blobs
12961 Misty C. Bentz, Georgia State University Research Foundation A Cepheid Distance to NGC6814
12963 Tracy Beck, Space Telescope Science Institute Spatially Resolving the Disk Mass Accretion Process In Young Star Binaries
12974 Matthew Mechtley, Arizona State University WFC3IR Imaging of UV-Faint z=6 Quasars: Star-Forming Host Galaxies of AGN in the Early Universe
13003 Michael D. Gladders, University of Chicago Resolving the Star Formation in Distant Galaxies
13025 Andrew J. Levan, The University of Warwick Unveiling the progenitors of the most luminous supernovae
13050 Remco van den Bosch, Max-Planck-Institut fur Astronomie, Heidelberg The Most Massive Black Holes in Small Galaxies
13062 Howard E. Bond, The Pennsylvania State University HST Observations of Astrophysically Important Visual Binaries
13176 Daniel Apai, University of Arizona Extrasolar Storms: The Physics and Chemistry of Evolving Cloud Structures in Brown Dwarf Atmospheres
13229 Zolt Levay, Space Telescope Science Institute Hubble Heritage imaging of Comet ISON
13293 Anne Jaskot, University of Michigan Green Pea Galaxies: Extreme, Optically-Thin Starbursts?
13297 Giampaolo Piotto, Universita degli Studi di Padova The HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation
13302 J. Michael Shull, University of Colorado at Boulder COS Spectra of High-Redshift AGN: Probing Deep into the Rest-Frame Ionizing Continuum and Broad Emission Lines
13305 Carolin Villforth, University of St. Andrews Do mergers matter? Testing AGN triggering mechanisms from Seyferts to Quasars
13307 Nadia L Zakamska, The Johns Hopkins University Taking the measure of quasar winds
13326 Ragnhild Lunnan, Harvard University Zooming In on the Progenitors of Ultra-Luminous Supernovae with HST
13329 Jonathan D. Nichols, University of Leicester Discovering the nature of the star-planet interaction at WASP-12b
13335 Adam Riess, The Johns Hopkins University HST and Gaia, Light and Distance
13343 David Wittman, University of California - Davis Probing Dark Matter with a New Class of Merging Clusters
13404 William M. Grundy, Lowell Observatory Mutual Orbits and Physical Properties of Binary Transneptunian Objects
13417 David P. Bennett, University of Notre Dame Measuring the Exoplanet Mass Function Beyond the Snow-Line
13420 Guillermo Barro, University of California - Santa Cruz The progenitors of quiescent galaxies at z~2: precision ages and star-formation histories from WFC3/IR spectroscopy
13472 Wendy L. Freedman, Carnegie Institution of Washington The Hubble Constant to 1%? STAGE 4: Calibrating the RR Lyrae PL relation at H-Band using HST and Gaia Parallax Stars
13476 Nitya Kallivayalil, The University of Virginia Proper Motion and Internal Kinematics of the SMC: are the Magellanic Clouds bound to one another?
13490 Jason A. Surace, California Institute of Technology Resolving the Reddest Extragalactic Sources Discovered by Spitzer: Strange Dust-Enshrouded Objects at z~2-3?
13492 Harold A. Weaver, The Johns Hopkins University Applied Physics Laboratory Hubble Spectroscopy of Sungrazing Comet ISON

Selected highlights

GO 12903: The Evolutionary Link Between Type 2 and Type 1 Quasars

Artist's impression of the black hole and surrounding torus in an AGN
This year (2013) is the fiftieth anniversary of the recognition that QSOs (quasars, quasi-stellar objects) were extremely luminous objects lying at substantial redshifts. The central engine powering these luminous objects is now recognised as a supermassive black hole, marking the central regions of a galaxy. As such, QSOs are clearly related to (and more luminous than) active galactic nuclei (AGN). Like AGNs, QSOs have been segregated into two categories based on their spectral properties: systems with broad lines are characterised as Type 1 QSOs; systems with narrow lines are classed as Type 2. As with AGN, the underlying cause of these differences is generally believed to reside more in our perspective than on the sources themselves: heavily obscured systems, where the central accretion disk lies behind a thick veil of dust, are observed as Type 2 systems; they are expected to evolve to form Type 1 systems as the dust is ablated and destroyed. The present SNAP program aims to test this scenario by coupling mid-infrared Herschel observations, probing the dust environment, with HST near-infrared WFC3 imaging of targets drawn from two matched samples of Type 1 and Type 2 QSOs.

GO 13329: Discovering the nature of the star-planet interaction at WASP-12b

Artist's conception of atmospheric ablation on a hot jupiter Among the most surprising discoveries of the latter part of the twentieth century was the finding that exoplantery systems were not simple copies of the Solar System architecture. Specifically, Jovian-mass gas giants were a relatively common occurrence at sub-Mercurian separations from sun-like stars. Characterised as "hot jupiters", the hottest jupiter is the ~1.4 MJup planet in a 1.1 day period orbit around a fairly anonymous 11th magnitude G dwarf. This is a transiting system, identified by the WASP team and designated as WASP-12b, so the orbital inclination is known, and the absolute semi-major axis is only 0.023 AU, less than one-tenth the radius of Mercury's orbit. Consequently, WASP-12b experiences substantial heating, and is estimated to have a temperature of ~2500K (comparable with an M7/M8 dwarf). At these temperatures, the expectation is that the planetary atmosphere will be subject to extensive evaporation, potentially leading to a substantial gas tail. In Cycle 17, COS was used to observe this system, and the results appeared to indicate that the transit ingress occurs earlier at near-UV wavelengths than at optical wavelengths;that is, the planet seems to have a larger cross-section in the near-UV. The same phenomenon was not observed at transit egress. A possible explanation for this effect is that the planet has a substantial magnetic field, which concentrates dense shocked material in the supersonic stellar wind upstream of the field. If so, this could provide a mechanism for not only probing the origins of magnetic fields in exoplanets, but also constraining the interior structure of the planet. The data from the Cycle 17 program, however, are sparse. The present program aims to confirm the results through observations of additional transits.

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 13492: Hubble Spectroscopy of Sungrazing Comet ISON

HST image of Comet ISON, late April 2013
At least once every decade, the astronomical community gets excited by the discovery of a comet that offers the prospect of becoming a "comet of the century", developing a spectacular tail speading across the sky at sunset or sunrise. Unfortunately, while Comet McNaught put on a spectacular shows for the southern hemisphere in 2007, most of the predicted rivals of the Great Comets of 1680/1811/1882 have fizzled. The latest in line is Comet ISON. Discovered in late 2012 when it lay beyond jupiter's orbit, the comet is scheduled to pass within 700,000 miles of the Sun on November 28th. Despite its distance, at that time the comet already had a substahtial coma and tail, leading to hopes that it might be highly volatile rich. However, subsequent observations have shown that the brightness has increased at a slower rate than hoped for, suggesting that Comet ISON may prove to be another disappointment - at least for the public. The comet passed interior to Mars' orbit in late September, and will cross the Earth's orbit on its inward journey around November 2nd. As a sun-grazer, there is a significant chance that the comet might break up close to perihelion, potentially offering an even more spectacular show and more volatiles are exposed to solar radiation. Hubble caught observations of Comet ISON in April, before it entered the solar avoidance zone, withi 50 degrees of the Sun.The comet has become accessible again for most of October, and the present program will use STIS and COS to obtain ultraviolet spectra of the pre-perihelion gases.

Past weeks:
page by Neill Reid, updated 14/10/2012
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