This week on HST


HST Programs: April 21 - April 27, 2014

Program Number Principal Investigator Program Title
12903 Luis C. Ho, Carnegie Institution of Washington The Evolutionary Link Between Type 2 and Type 1 Quasars
13024 John S. Mulchaey, Carnegie Institution of Washington A Public Snapshot Survey of Galaxies Associated with O VI and Ne VIII Absorbers
13046 Robert P. Kirshner, Harvard University RAISIN: Tracers of cosmic expansion with SN IA in the IR
13058 Kailash C. Sahu, Space Telescope Science Institute Accurate Mass Determination of the Old White Dwarf G105-30 through Astrometric Microlensing
13297 Giampaolo Piotto, Universita degli Studi di Padova The HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation
13298 Richard M. Plotkin, University of Michigan Radio-quiet Quasars with Extremely Weak Emission Lines: a New Perspective on Quasar Unification
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
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
13312 Danielle Berg, University of Minnesota - Twin Cities The Evolution of C/O in Low Metallicity Dwarf Galaxies
13315 Marc W. Buie, Southwest Research Institute Pluto Satellite Orbits in Support of New Horizons
13324 Davor Krajnovic, Astrophysikalisches Institut Potsdam Where cores are no more: assessing the role of dissipation in the assembly of early-type galaxies
13330 Bradley M Peterson, The Ohio State University Mapping the AGN Broad Line Region by Reverberation
13357 David J. Radburn-Smith, University of Washington Feeding Galaxies: Cold Accretion Through Warps
13364 Daniela Calzetti, University of Massachusetts - Amherst LEGUS: Legacy ExtraGalactic UV Survey
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
13376 Kristen McQuinn, University of Minnesota - Twin Cities The Star Formation History of Leo P
13399 Asantha Cooray, University of California - Irvine Spatially Resolved WFC3/Grism Spectral Line Imaging of Gravitational Lensed Herschel-selected Luminous Dusty Starbursts
13409 Richard Mushotzky, University of Maryland Hubble Observations of Kepler-Monitored Seyfert Is
13412 Tim Schrabback, Universitat Bonn, Argelander Institute for Astronomy An ACS Snapshot Survey of the Most Massive Distant Galaxy Clusters in the South Pole Telescope Sunyaev-Zel'dovich Survey
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
13442 R. Brent Tully, University of Hawaii The Geometry and Kinematics of the Local Volume
13467 Jacob L. Bean, University of Chicago Follow The Water: The Ultimate WFC3 Exoplanet Atmosphere Survey
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
13614 Joaquin Vieira, University of Illinois at Urbana - Champaign High-Redshift Starburst Galaxies Under the Cosmic Microscope: Unveiling the stellar histories of strongly lensed starburst galaxies
13620 William B. Sparks, Space Telescope Science Institute Probing the atmosphere of a transiting ocean world: are there ice fountains on Europa?
13629 Yael Naze, Universite de Liege Characterizing the high-energy properties of a highly magnetized star
13630 Christian Knigge, University of Southampton Time-Resolved Ultraviolet Spectroscopy of the Missing Link Pulsar/LMXB PSR J1023
13631 Amy Simon-Miller, NASA Goddard Space Flight Center Dynamical Change in Jupiter's Great Red Spot

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 13330: Mapping the AGN Broad Line Region by Reverberation


Simulations of the appearance and velocity structure within an AGN disk (see Keith Horne's web page).
Active galaxies (AGNs) are generally luminous systems, characterised by the presence of strong nuclear emission lines of numerous species including H, He I, He II, and Fe, Ca, O, C and S over a range of ionisations. These features originate from gas clouds in the nuclear regions, with the energy supplied through accretion onto a central massive black hole. The high-temperature, rapidly-rotating gas clouds nearest the central engine are responsible for producing broad emission lines (hence, the "Broad Line Region"). The structure of the BLR can be discerned using a technique known as reverberation mapping: variations in the accretion rate lead to fluctuations in luminosity; those variations lead, in turn, to variations in the photoionisation of the BLR, and corresponding changes in spectral line strengths and velocities; monitoring those changes, and correlating them with the photometric variability of the central source, measures the light travel time from nucleus to BLR gas, and hence maps the size of the BLR. The present prorgam will use the Cosmic Origins Spectrograph to undertake systematic monitoring of the nuclear regions of the Seyfert I galaxy, NGC 5548. The first observations were taken on February 2nd 2014 and will run through July at a cadence of one orbit per day for 179 days.

GO 13620: Probing the atmosphere of a transiting ocean world: are there ice fountains on Europa?


An image of Europa taken by Voyage 2 in 1979
Europa is the smallest, and the most intriguing, of the four Galilean satellites of Jupiter. With a diameter of 3139 km, Europa is almost twice the size of Earth's moon and significantly larger than Mercury. In 1957, Gerard Kuiper commented that both infrared spectroscopy and the optical colours and albedo suggested that Jovian satellite II (Europa) is covered "by H2O snow". Images taken by the Voyager space probes in the late 1970s (see left) reveal a smooth surface, with only a handful of craters larger than a few kilometres. These features are consistent with a relatively young, icy surface. Subsequent detailed investigations by the Galileo satellite strongly suggest that a substantial body of liquid water, heated by tidal friction, underlies a 5 to 50 km thick icy crust. The presence of this subterranean (subglacial?) ocean clearly makes Europa one of the two most interesting astrobiology targets in the Solar System. Most recently, analysis of observations taken by the Space Telescope imaging Spectrograph (STIS) on Hubble indicated the presence of an extended cloud of Lyman-alpha emission near the polar regions while Europa was furthest in its orbit from Jupiter, stongly suggesting that Europa's oceans may be vaporising into space. The present HST program also aims to search for outgassing, but in this by looking for absorption features against the smooth background light of Juptier while Europa is in transit. This DD program follows upon GO 134338, using STIS in time-tag mode to search from transient features in the far-UV, and applying coronagraphy at near-UV wavelengths to look for dust signatures.

GO 13467: Follow The Water: The Ultimate WFC3 Exoplanet Atmosphere Survey


Probing the atmosphere of a transiting exoplanet
The first exoplanet, 51 Peg b, was discovered in 1995 through high-precision radial velocity measurements. 51 Pegb was followed by a trickle, and then a flood of other discoveries, as astronomers realised that there were other solar systems radically different from our own, where "hot jupiters" led to short-period, high-amplitude velocity variations. Then, in 1999, came the inevitable discovery that one of those hot jupiters. HD 209458b, was in an orbit aligned with our line of sight to the star, resulting in transits. Since that date, the number of known transiting exoplanet systems has grown to more than 400 in over 300 planetary systems, with the overwhelming majority identified by the Kepler satellite, which has also contributed close to 3,000 additional (very strong) candidates. As these observations have accumulated,the broad diversity of exoplanet systems has become increasingly apparent. Transiting systems are invaluable, since they provide not only unambiguous measurements of mass and diameter, but also an opportunity to probe the atmospheric structure by differencing spectra taken during and between primary secondary transit. Such observations are best done from space: indeed, while high-precision ground-based observations have succeeded in constraining atmospheric properties in a few systems, the only successful detections of atmospheric features to date have been with HST and Spitzer. HST capabilities have been enhanced in the last few years with addition of spatial scanning, moving the target star over the chip in a controlled fashion during an observation. This allows observers to accumulate images or spectra of substantially higher signal-to-noise, a crucial advantage if one is looking for flux differences of elss than 1 part in 104. Past programs have accumulated observations of over a dozen exoplanets, using STIS at optical wavelengths and WFC3 in the near-infrared. The present program targets eight exoplanet systems with a diverse range of properties: HD 209458b,GL 3470b, HAT-P-26b, WASP-12b, WASP-18b, WASP-43b, WASP-80b and WASP-19b. The WFC3-IR G141 grism will be used to search for the characteristic near-infrared spectral features due to water in the amospheres of these exoplanets.

Past weeks:
page by Neill Reid, updated 3/5/2014
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