This week on HST


HST Programs: April 7 - April 13, 2014

Program Number Principal Investigator Program Title
13230 Andrew J. Levan, The University of Warwick A supernova in the brightest gamma-ray burst
13297 Giampaolo Piotto, Universita degli Studi di Padova The HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation
13299 Jacqueline Radigan, Space Telescope Science Institute Silver Linings: Using Cloud Maps to Understand the L/T Spectral Transtion
13303 Robert A Simcoe, Massachusetts Institute of Technology The Structure of MgII Absorbing Galaxies at z=2-5: Linking CGM Physics and Stellar Morphology During Galaxy Assembly
13305 Carolin Villforth, University of St. Andrews Do mergers matter? Testing AGN triggering mechanisms from Seyferts to Quasars
13309 Yicheng Guo, University of California - Santa Cruz UV Snapshot of Low-redshift Massive Star-forming Galaxies: Searching for the Analogs of High-redshift Clumpy Galaxies
13315 Marc W. Buie, Southwest Research Institute Pluto Satellite Orbits in Support of New Horizons
13330 Bradley M Peterson, The Ohio State University Mapping the AGN Broad Line Region by Reverberation
13332 Seth Redfield, Wesleyan University A SNAP Survey of the Local Interstellar Medium: New NUV Observations of Stars with Archived FUV Observations
13343 David Wittman, University of California - Davis Probing Dark Matter with a New Class of Merging Clusters
13346 Thomas R. Ayres, University of Colorado at Boulder Advanced Spectral Library II: Hot Stars
13347 Joel N. Bregman, University of Michigan The Missing Baryons Around Nearby Dwarf Galaxies
13350 Andrew S. Fruchter, Space Telescope Science Institute How Low Can They Go? Detecting low luminosity supernova progenitors
13352 Matthew A. Malkan, University of California - Los Angeles WFC3 Infrared Spectroscopic Parallel Survey WISP: A Survey of Star Formation Across Cosmic Time
13364 Daniela Calzetti, University of Massachusetts - Amherst LEGUS: Legacy ExtraGalactic UV Survey
13382 Mary E. Putman, Columbia University in the City of New York Warm Gas Flows in the Coma Cluster
13389 Brian Siana, University of California - Riverside The Ultraviolet Frontier: Completing the Census of Star Formation at Its Peak Epoch
13393 Dennis Zaritsky, University of Arizona Galaxy Transformation in the Infall Regions of Clusters
13396 Sarah V. Badman, Lancaster University Dual views of Saturn's UV aurora: revealing magnetospheric dynamics
13398 Christopher W. Churchill, New Mexico State University A Breakaway from Incremental Science: Full Characterization of the z<1 CGM and Testing Galaxy Evolution Theory
13418 Daniel Apai, University of Arizona Patchy Clouds and Rotation Periods in Directly Imaged Exoplanets
13442 R. Brent Tully, University of Hawaii The Geometry and Kinematics of the Local Volume
13443 Roeland P. van der Marel, Space Telescope Science Institute Proper Motions along the Orphan Stream: Finding the Parent, Orbit, and Milky Way Halo Shape
13445 Joshua S. Bloom, University of California - Berkeley Absolute Calibration of the Extragalactic Mira Period-Luminosity Relation
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
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
13493 Tim Schrabback, Universitat Bonn, Argelander Institute for Astronomy An XMM-Newton+HST study of the likely most X-ray luminous z>=0.9 galaxy cluster
13510 Martin C. Weisskopf, NASA Marshall Space Flight Center Joint Chandra and HST Monitoring and Studies of the Crab Nebula
13517 Matthew A. Malkan, University of California - Los Angeles WFC3 Infrared Spectroscopic Parallel Survey WISP: A Survey of Star Formation Across Cosmic Time

Selected highlights

GO 13299: Silver Linings: Using Cloud Maps to Understand the L/T Spectral Transition


An artist's rendition of brown dwarf atmospheric structure
Brown dwarfs are failed stars - objects that form like stars, by gravitational collapse within giant molecular clouds, but which have insufficient mass to raise the central temperature above 107 K, and which therefore are unable to ignite hydrogran fusion and maintain a long-lived central energy source. As such, these objects reach a maximum surface temperature of perhaps 3,000K some tens of millions of years after their formation, and subsequently cool and fade into oblivion. As they cool, they move through spectral types M, L and T, with the oldest brown dwarfs now likely to have temperatures close to 300K and emergent spectra characterised by water and ammonia bands, the putative signatures of the spectral class Y. As these dwarfs cool from L to T (~1500 to ~1200K), the atmospheres undergo significant changes, with heavier elements condensing to form dust. That dust can form clouds, perhaps giving the dwarf's surface a banded appearance, similar to Jupiter. The clouds themselves may appear and disappear over relatively short timescales, leading to photometric variations at particular wavelengths. Past programs have used both Spitzer and HST to monitor spectral variability in a number of systems, primarily objects with spectral types in the L/T transition zone. . The present program further broaden the sample by monitoring three brown dwarfs for variability using time-resolved WFC3 grism G141 spectroscopy.

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 13445: Absolute Calibration of the Extragalactic Mira Period-Luminosity Relation


The spiral galaxy, NGC 4258, as imaged by GALEX
Defining a reliable cosmic distance scale remains one of the most important tasks facing modern cosmologists. Cepheid variable stars have been the prime extragalactic distance indicator since Henrietta Leavitt's discovery of the period-luminosity relation described by Cepheids in the Small Magellanic Cloud. It was Hubble's identification of Cepheids in NGC 6822 that finally established that at least some nebulae were island universes. Cepheids. Cepheids are not the only pulsating variables that can serve as distance indicators, however: RR Lyraes serve as distance indicators for old populations; and pulsating red giant variables offer an alternatiev in intermediate-age populations. Most long period variable stars (LPVs) are red giants on the asymptotic giant branch (AGB). These are intermediate mass stars, between ~1.5 and ~7 solar masses, that are powered by hydrogen and helium shell-burning. The interactions between the two energy sources lead to instabilities that can generate substantial pulsations, with periods from ~50 to ~500 days. Mira, or omicron Ceti, is the Galactic prototype for this type of variable, and numerous LPVs have been identified throughout the Milky Way and in the neighbouring Small and Large Magellanic Clouds. The LMC and SMC variables show a clear period-luminosity relation, particularly at near-infrared wavelengths, with longer period stars having higher intrinsic luminosities. This P-L relation, while not as well established for classical cepheids, allows LPVs to contribute to measurements of the extragalactic distance scale, particularly since miras are more luminous than Cepheids at inreared wavelengths. The present program aims to capitalise on these characteristics by using the WFC3 IR camera to search for mira variables in NGC 4258, a spiral galaxy that hosts several megamaser sources that enable accuate distance measurements. The aim is to use these miras to define a period-luminosity relation that can serve as a reference point for measuring distances to more distant galaxies.

Past weeks:
page by Neill Reid, updated 7/2/2014
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