This week on HST

HST Programs: August 18 - August 24, 2014

Program Number Principal Investigator Program Title
12893 Ronald L Gilliland, The Pennsylvania State University Study of Small and Cool Kepler Planet Candidates with High Resolution Imaging
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
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
13332 Seth Redfield, Wesleyan University A SNAP Survey of the Local Interstellar Medium: New NUV Observations of Stars with Archived FUV Observations
13352 Matthew A. Malkan, University of California - Los Angeles WFC3 Infrared Spectroscopic Parallel Survey WISP: A Survey of Star Formation Across Cosmic Time
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
13401 Claes Fransson, Stockholm University A 3D view of the SN 1987A Ejecta
13407 Crystal Martin, University of California - Santa Barbara COS Gas Flows: Challenging the Optical Perspective
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
13442 R. Brent Tully, University of Hawaii The Geometry and Kinematics of the Local Volume
13459 Tommaso L. Treu, University of California - Los Angeles The Grism Lens-Amplified Survey from Space {GLASS}
13462 Brian E. Wood, Naval Research Laboratory Tracking the Winds of Red Giants from the Star to the ISM
13463 Kailash C. Sahu, Space Telescope Science Institute Detecting and Measuring the Masses of Isolated Black Holes and Neutron Stars through Astrometric Microlensing
13496 Jennifer Lotz, Space Telescope Science Institute HST Frontier Fields - Observations of MACSJ0416.1-2403
13517 Matthew A. Malkan, University of California - Los Angeles WFC3 Infrared Spectroscopic Parallel Survey WISP: A Survey of Star Formation Across Cosmic Time
13611 Nial R. Tanvir, University of Leicester The nature of the low redshift ultra-long GRB130925A: core collapse or tidal disruption?
13633 John R. Spencer, Southwest Research Institute A Kuiper Belt Object for the New Horizons Mission
13748 Luigi R. Bedin, Osservatorio Astronomico di Padova Astrometric search for Planets in the closest Brown Dwarf Binary system Luhman 16AB
13751 Andrea De Luca, INAF, Instituto di Astrofisica Spaziale e Fisica Imaging the Crab nebula when it is flaring in gamma-rays
13863 Dean C. Hines, Space Telescope Science Institute Imaging Polarimetry of the 67P/Churyumov-Gerasimenko with ACS: Supporting the Rosetta Mission

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 13459: The Grism Lens-Amplified Survey from Space {GLASS}

HST imaging of the galaxy cluster MACS0717.5-3745
The overwhelming majority of galaxies in the universe are found in clusters. As such, these systems offer an important means of tracing the development of large-scale structure through the history of the universe. Moreover, as intense concentrations of mass, galaxy clusters provide highly efficient gravitational lenses, capable of concentrating and magnifying light from background high redshift galaxies to allow detailed spectropic investigations of star formation in the early universe. Hubble imaging has already revealed lensed arcs and detailed sub-structure within a handful of rich clusters. At the same time, the lensing characteristics provide information on the mass distribution within the lensing cluster. Hubble is currently undertaking deep imaging observations of up to 6 galaxy clusters as part of the Frontier Fields Director's Discretionary Time program (GO 13495). The present program supplements those visual and near-infrared data by adding imaging spectrophotometry at near-infrared wavelengths, using the low-resolution G102 and G141 grisms on the WFC3-IR camera. In all, the program targets 10 clusters drawn from both the Frontier Fields sample and from the larger-scale (but less deep) multicolour CLASH program. The goal is to identify and characterise galaxies at relatively high redshifts, close to the epoch of reionisation. The grism data should provide low-resolution spectra for 150-200 galaxies at redshifts z>6, with the potential to detect Lyman alpha emission at redshifts up to z~8.5. The present observations target the Frontier Fields cluster, MACS0717.5+3745.

GO 13633: A Kuiper Belt Object for the New Horizons Mission

Hubble Space Telescope images of the Pluto system, including the recently discovered moons, P4 and P5
The Kuiper Belt lies beyond the orbit of Neptune, extending from ~30 AU to ~50 AU from the Sun, and includes at least 70,000 objects with diameters exceeding 100 km. Setting aside Pluto, the first trans-Neptunian objects were discovered in the early 1990s. Most are relatively modest in size, with diameters of a few hundred km and photometric properties that suggest an icy composition, similar to Pluto and its main satellite, Charon. In recent years, a handful of substantially larger bodies have been discovered, with diameters of more than 1000 km; indeed, one object, Eris (2003 UB13), is slightly larger than Pluto (2320 km) and 25% more massive. We know the mass for Eris because it has a much lower mass companion, Dysnomia, which orbits Eris with a period of 16 days (see this recent press release ). Pluto itself has at least 5 companions: Charon, which is about 1/7th the mass of Pluto, and the much smaller bodies, Hydra, Nix, P4 and P5 discovered through HST observations within the last few years. The New Horizons Mission was launched on January 19th 2006 with the prime purpose of providing the first detailed examination of Pluto. The Pluto encounter represents the first phase of the originally-proposed mission. Following the fly-by, set for Bastille day in 2015, the aim is to re-direct New Horizons towards one or more smaller members of the Kuiper Belt, with the goal of providing a closer look at these icy bodies. However, New Horizons needs to identify an appropriate target - a KBO with orbital parameters such that New Horizons can use its modest complement of remaining fuel to reach the target. Adding a further complication, Pluto happens to lie within 5 degrees of the Galactic Plane and the consequent high star density has proven a barrier to deep ground-based searches. As a consequence, the New Horizons team was awarded Hubble time to search an area roughly the size of the full moon for a suitable target. These observations are significantly deeper than previous surveys, and as a result will lead to a better understanding of the size distribution of smaller objects (< 20 km diameter) in the Kuiper Belt.

GO 13863:Imaging Polarimetry of the 67P/Churyumov-Gerasimenko with ACS: Supporting the Rosetta Mission

Rosetta image of Comet 67P/Churymunov-Gerasimenko
The Rosetta mission is an ESA-led space mission that was launched in 2 March 2004 with the aim of making a rendezvous with a comet and dropping a small lander onto its surface. The original target was Comet 46P/Wirtanen, but problems with the Ariane launch vehicle led to launch delays, and Rosetta was re-targeted towards a different comet, 67P/Churyumov-Gerasimov. Achieving that rendezvous demanded a complex path through the solar system, with Rosetta undertaking a series of close passages of Mars and Earth that were designed to boost its velocity to sufficiently high values to match the comet. Those measures were successful, and the rendezvous occuring in early August, with Rosetta sending back spectacular pictures of the boot-shaped 67P. The present HST program is one of several using various facilities that aim to provide complementary data. The Advanced Camera for Surveys (ACS) is obtaining polarised images that can be used to probe the dust content in the coma in the immediate vicinity of the nucleau. HST's unparalleled angular resolution at optical wavelengths give it a significant advantage over larger ground-based telescopes.

Past weeks:
page by Neill Reid, updated 26/8/2014
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