This week on HST


HST Programs: April 10 - April 16, 2017

Program Number Principal Investigator Program Title
14096 Dan Coe, Space Telescope Science Institute - ESA RELICS: Reionization Lensing Cluster Survey
14114 Pieter van Dokkum, Yale University A Wide-Field WFC3 Imaging Survey in the COSMOS Field
14235 Sangmo Tony Sohn, Space Telescope Science Institute Globular Cluster Orbits from HST Proper Motions: Constraining the Formation and Mass of the Milky Way Halo
14594 Rich Bielby, Durham Univ. QSAGE: QSO Sightline And Galaxy Evolution
14606 Brooke Devlin Simmons, University of California - San Diego Secular Black Hole Growth and Feedback in Merger-Free Galaxies
14618 Michael Shara, American Museum of Natural History Ultraviolet Flashers in M87: Rapidly Recurring Novae as SNIa Progenitors
14643 Pieter van Dokkum, Yale University Imaging of three Ultra Diffuse Galaxies with measured stellar kinematics
14644 Pieter van Dokkum, Yale University Exploring the extremely low surface brightness sky: distances to 23 newly discovered objects in Dragonfly fields
14648 Adam Riess, The Johns Hopkins University A New Threshold of Precision, 30 micro-arcsecond Parallaxes and Beyond
14649 Katherine Anne Alatalo, Carnegie Institution of Washington Opening a New Window into Galaxy Evolution Through the Lens of CO-detected Shocked Poststarburst Galaxies
14652 Benne Willem Holwerda, University of Louisville Research Foundation, Inc. Super-Eight: The brightest z~8 Galaxies
14656 Ivana Orlitova, Astronomical Institute, Academy of Sciences of CR How does ionizing radiation escape from galaxies?
14658 Eric W. Peng, Peking University Massive Star Clusters and the Origin of Ultra-Diffuse Galaxies
14675 Julia Christine Roman-Duval, Space Telescope Science Institute - ESA Metal Evolution and TrAnsport in the Large Magellanic Cloud (METAL): Probing Dust Evolution in Star Forming Galaxies
14682 Bjorn Benneke, California Institute of Technology A Search for Methane, Ammonia, and Water on Two Habitable Zone Super-Earths
14694 Stephan Robert McCandliss, The Johns Hopkins University SDSSCGB-46589.1 -- a Lyman Alpha Blob at Low Redshift?
14704 Charlie Conroy, Harvard University A Year in the Whirlpool
14713 Raghvendra Sahai, Jet Propulsion Laboratory Binarity and Accretion Activity in AGB Stars with Variable UV and X-Ray Emission
14718 George D. Becker, University of California - Riverside The Metal-Enriched Environments of Galaxies Near Reionization
14738 Arunav Kundu, Eureka Scientific Inc. A Far Ultraviolet Study of Globular Clusters in NGC 3115
14759 Thomas M. Brown, Space Telescope Science Institute What Happens in the Atmospheres of Hot Horizontal Branch Stars Near 20, 000K?
14767 David Kent Sing, University of Exeter The Panchromatic Comparative Exoplanetary Treasury Program
14772 Bart P. Wakker, University of Wisconsin - Madison Observing gas in Cosmic Web filaments to constrain simulations of cosmic structure formation
14782 Lorenzo Pino, Universita degli Studi di Padova Is the atmosphere of the extremely irradiated exoplanet WASP-43b in a blow-off state?
14840 Andrea Bellini, Space Telescope Science Institute Schedule Gap Pilot
14886 Russell Julian Smith, Durham Univ. The unusual lensing BCG in Abell 1201: A steep IMF gradient, or an ultra-massive central black hole?
14891 William B. Sparks, Space Telescope Science Institute Confirming the ice plumes of Europa
14922 Patrick Kelly, University of California - Berkeley Probing the Nature of Dark Matter with Individual Stars Highly Magnified by a Galaxy Cluster

Selected highlights

GO 14235: Globular Cluster Orbits from HST Proper Motions: Constraining the Formation and Mass of the Milky Way Halo


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. A substantial number of thee systems show complex structure in the colour-magnitude diagram, indicating the presence ofmultiple stellar populations. Current globulars may therefore represent the remnant cores of dwarf galaxy-like systems. Regardless of their origin, the present systems can also serve to map the potential of the Milky Way. Undertaking that analysis demands the determination of three-dimensional motions, requiring that we obtain accurate absolute proper motions for these systems. That is now becoming possible; thanks to Hubble's longevity, a significant number of clusters have imaging data from 10-20 years ago. Coupled with new observations, those data provide the baseline to allow measurement of the tranverse motion, and hence orbit determinations.

GO 14644: Exploring the extremely low surface brightness sky: distances to 23 newly discovered objects in Dragonfly fields


The elliptical galaxy, NGC 1052
The Dragonfly telescope is a cluster of 10 400-mm Canon lenses that produces wide-field images that are optimised to detect low-durface brightness objects. The telescope was previously used to survey the regions around M101, where it detected seven potential companions that were targeted for deep Hubble imaging. The HST data showed that three systems were indeed low-luminosity companions of M101, while the other four are Ultra Diffuse Galaxies at greater distances. Dragonfly has now been used to target fields centred on NGC 1052, NGC 1084, NGC 3384 and NGC 4258. Those observations have revealed 22 candidate companion galaxies in the four fields. If associated with the parent galaxies, the galaxies are very similar to the low-surface brightness dwarfs found within the Milky Way system. The present program aims to obtain ACS images of the systems, recolving individual stars and hence determining their distance through the location of the tip of the red giant branch.

GO 14682: A Search for Methane, Ammonia, and Water on Two Habitable Zone Super-Earths


Artist's impression of a planet an M dwarf system
The first exoplanet, 51 Peg b, was discovered through radial velocity measurements in 1995. The succeeding two decades saw first 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. In 1999 the first transiting system, HD 209458b, was discovered.Increasing precision led to discoveries of lower mass planets and systems around lower-mass stars. The Kepler satellite, in particular, has made major contributions in this area, adding close to 3,000 confirmed exoplanets, both in its original incarnation and more recently in the extended Kepler 2 mission. These transiting systems are invaluable not only in providing unambiguous measurements of mass and diameter, but also in providing 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, the only successful atmospheric observations to date have been with HST and Spitzer. The current program focuses on two "super-Earths" discovered in the Kepler 2 survey: K2-3d (1.6 Earth radii, 11.1 Earth masses) and K2-18b (2.24 Earth radii, no precise mass). In both cases, the parent star is an M-dwarf: K2-3 is one of three planets circling an M0 dwarf lying at a distance of ~40 parsecs; K2-18b is the as-yet only known companion of a more distant M0 dwarf. Both planets have orbits that lie within the nominal habitable zones of the parent stars. The present program will use the WFC3/IR grisms to map the near-IR spectral energy distribution through several transits, searching for characteristic features due to water, ammonia and (perhaps) methane, probing the relative atmospheric structure of these systems.

GO 14891: Confirming ice plumes of Europa


The HST imaging of a potential water plume around Europa's south pole superimposed on an image of the satellite
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, strongly suggesting that Europa's oceans may be vaporising into space.Follow-up observations on two further occasions earlier in 2014 failed to detect any emission, suggesting that the emission is either sporadic or periodic; in the latter case, the emission might be related to the location of Europa within its orbit and the consequent tidal strain imposed by Jupiter. Over the past year, Hubble has monitored Europa' activity through several programs. The present program is using UV imaging with the Space Telescope Imaging Spectrograph to search for absorption features as Europa transits across Jupiter.

Past weeks:
page by Neill Reid, updated 2 /1/2017
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