This week on HST


HST Programs: December 26 - January 1, 2017

Program Number Principal Investigator Program Title
13847 Kailash C. Sahu, Space Telescope Science Institute Determining the Mass of Proxima Centauri through Astrometric Microlensing
14080 Anne Jaskot, Smith College LyC, Ly-alpha, and Low Ions in Green Peas: Diagnostics of Optical Depth, Geometry, and Outflows
14093 Danielle Berg, University of Wisconsin - Milwaukee Stellar Populations and Physical Conditions at ~100 pc Resolution in a Lensed Galaxy at z ~ 4
14095 Gabriel Brammer, Space Telescope Science Institute - ESA Calibrating the Dusty Cosmos: Extinction Maps of Nearby Galaxies
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
14123 James Colbert, Jet Propulsion Laboratory Does All The Lyman Continuum Emission Escape From Young, Low Mass Starbursts?
14160 John M. O'Meara, Saint Michaels College A 100 million-fold increase in the measured sizes of neutral gas reservoirs in the early Universe
14164 Ata Sarajedini, University of Florida Exploring the nature and synchronicity of early cluster formation in the Local Group
14178 Matthew A. Malkan, University of California - Los Angeles WFC3 Infrared Spectroscopic Parallel Survey: The WISP Deep Fields
14190 Nuria Calvet, University of Michigan Trickles of Accretion: Catching a Final Glimpse of Gas in the Disk
14232 Ian U. Roederer, University of Michigan STIS Observations of Metal-Poor Stars: Direct Confrontation with Nucleosynthetic Predictions
14246 Douglas Russell Gies, Georgia State University Research Foundation The Fastest Rotating Stars
14248 Michael J Koss, Eureka Scientific Inc. Studying Dual AGN Activity in the Final Merger Stage
14269 Nicolas Lehner, University of Notre Dame Just the BASICs: Linking Gas Flows in the Circumgalactic Medium to Galaxies
14343 Nitya Kallivayalil, The University of Virginia Proper Motion and Internal Kinematics of the SMC: are the Magellanic Clouds bound to one another?
14365 Zhichao Xue, Louisiana State University and A & M College Is Muzzio 10 The Ex-Companion Star of the PSR B1509-58 Progenitor?
14456 Mark Brodwin, University of Missouri - Kansas City Determining the Role of Merging in the Growth of the Galaxy Cluster Population in the Massive and Distant Clusters of WISE Survey
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
14626 Mary Barsony, SETI Institute DASH Mapping of IC348: The IMF from 2 to 80 Jupiter Masses
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
14654 Peter Milne, University of Arizona A Second Ladder: Testing for Bias in the Type Ia Distance Scale with SBF
14667 Hsiao-Wen Chen, University of Chicago Differentiating Gas Infall and Outflows with Resolved Star Formation Morphology
14677 Tim Schrabback, Universitat Bonn, Argelander Institute for Astronomy Probing the most distant high-mass galaxy clusters from SPT with HST weak lensing observations
14704 Charlie Conroy, Harvard University A Year in the Whirlpool
14706 Eilat Glikman, Middlebury College Testing the Triggering Mechanism for Luminous, Radio-Quiet Red Quasars in the Clearing Phase: A Comparison to Radio-Loud Red Quasars
14709 Brian Mazur, University of Toledo HST/WFC3 Spectroscopy of < 400 AU Companions to Orion Young Stellar Objects
14734 Nitya Kallivayalil, The University of Virginia Milky Way Cosmology: Laying the Foundation for Full 6-D Dynamical Mapping of the Nearby Universe
14757 Zach K. Berta-Thompson, University of Colorado at Boulder Hydrogen Escape from a Rocky Earth-Size Exoplanet
14779 Melissa Lynn Graham, University of Washington A NUV Imaging Survey for Circumstellar Material in Type Ia Supernovae
14793 Jacob L. Bean, University of Chicago The First Precise Atmospheric Metallicity Measurement for a Sub-Jovian Exoplanet
14840 Andrea Bellini, Space Telescope Science Institute Schedule Gap Pilot
14844 Chris S. Kochanek, The Ohio State University Dust to Dust: Monitoring the Evolution of a New Class of Self-Obscured Transients
14873 Julien de Wit, Massachusetts Institute of Technology Exploratory observations of the TRAPPIST-1 system: essential prelude to an immediate JWST follow-up
14884 Jessica Agarwal, Max Planck Institute for Solar System Research Characterising the dust ejection process in the first known active binary asteroid system 288P/300163.

Selected highlights

GO 14080: LyC, Ly-alpha, and Low Ions in Green Peas: Diagnostics of Optical Depth, Geometry, and Outflows


A montage of green pea galaxies discovered by the Galaxy Zoo project
Understanding the galaxy formation and galaxy evolution has been a strong focus of astronomical research since thne 1970s and remains a key issue for 21st century astrophysics. Since we cannot follow an individual galaxy through time, tackling these questions requires a statistical approach, and, as a result, large-scale surveys have played a crucial role in the field. In particular, the Sloan Digital Sky Survey, conducted from Apache point Observatory from the 1990s through the early years of this century, has provided a treasure trove of information of galaxies at low and moderate redshifts. One of the interesting discoveries that originated from SDSS was the discovery of so-called "green pea" galaxies - compact objects whose combined images have a greenish hue, originally uncovered by citizen scientists as part of the Galaxy Zoo project. Closer inspection shows that these are gas-rich galaxies lying at relatively low redshifts, 0.1 < z < 0.36, with the green-tinged hue partly stemming from the presence of strong oxygen ([O III]) emission. These characteristics indicate that the galaxies are undergoing strong star-forming episodes. The present program aims to take advantage of HST's unparalleled resolution and extraordinary sensitivity at ultraviolet wavelengths, and will use the Cosmic Origins Spectrograph to obtain spectra are far-UV wavelengths. Those observations will probe optical depth, the geometry of neutral gas and radiative transfer within these systems, revealing the physical structure of the underlying star forming regions and potentially offering insight into the nature of high redshift lyman-alpha emitters.

GO 14269: Just the BASICs: Linking Gas Flows in the Circumgalactic Medium to Galaxies


A computer simulation of galactic gas accretion and outflow
Galaxy formation, and the overall history of star formation within a galaxy, clearly demands the presence of gas. The detailed evolution therefore depends on how gas is accreted, recycled, circulated through the halo and, perhaps, ejected back into the intergalactic medium. Tracing that evolutionary history is difficult, since gas passes through many different phases, some of which are easier to detect than others. During accretion and, probably, subsequent recycling, the gas is expected to be reside predominantly at high temperatures. The most effective means of detecting such gas is through ultraviolet spectroscopy, where gas within nearby systems can be detected as absorption lines superimposed on the spectra of more distant objects, usually quasars. Extensive observations of galaxies at modest redshift (0.15 < z < 0.35) have shown that material extends to radii of hundreds of kpc, with a total mass in metals that is at least comparable with the mass in the central galaxy. The structures appear to show a bimodal metallicity distribution, with a metal-rich (~40% solar) component that may reflect winds and outflows, and a metal-poor (3% solar) component that may trace cold accretion streams. The present program aims to use ACS to image 14 QSO fields that harbour well-characterised circum-galactic medium absorbers, with the aim of measuring the geometry and morphology of the parent galaxies and searching for correlations with the gaseous properties.

GO 14648: A New Threshold of Precision, 30 micro-arcsecond Parallaxes and Beyond


HST WFPC2 image of NGC 4639, one of the Cepheid-rich spiral galaxies used to calibrate SNe Ia
The cosmic distance scale and dark energy are two key issues in modern astrophysics, and HST has played a vital role in probing both. On the one hand, HST has been involved in cosmic distance measurements since its inception, largely through the H0 Key Project, which used WFPC2 to identify and photometer Cepheids in 31 spiral galaxies at distances from 60 to 400 Mpc. On the other, HST is the prime instrument for investigating cosmic acceleration by searching for and following Type Ia supernovae at moderate and high redshift. These two cosmological parameters are directly related, and recent years have seen renewed interest in improving the accuracy of H0 with the realization that such measurements, when coupled with the improved constraints from the Cosmic Microwave Background, provide important constraints on cosmic acceleration and the nature of Dark Energy. Previous HST programs have focused on identifying and measuring light curves for cepheids in external galaxies (eg GO 10802 , GO 11570 ) or quantifying the effects of variations in intrinsic stellar parameters, such as metallicity (eg GO 10918 , GO 11297 ). The present SNAP program is part of a suite of HST programs focusing on the Galactic Cepheids that form the foundation for the whole distance ladder. These programs employ a revived version of an old technique to determine both accurate astrometry, hence trigonometric parallaxes and reliable distances, and accurate photometry, hence flux emasurements. The technique is drift-scanning - tracking HST during the observation so that stars form trails on the detector. This mode of observations was available in the early years of HST's operations, and has been revived primarily as a means of obtaining high signal-to-noise grism spectroscolpic data of stars hosting transiting exoplanets. However, the same technique can be used in imaging mode, and the extended trails allow not only multiple measurements of position differences for stars in the field but also extremely high signal-to-noise photometry. The latter is crucial in obtaining direct photometry of tghe local calibrations on the same HST system, the same system that is being used for photometry of Cepheids in the external galaxies that serve as the basis for the distance scale. Observations have been obtained for more than 20 such stars. The present program aims to refine the distance estimates by obtaining four additional epochs for 9 core Cepheids (Z Sct, DD Cas, VX Per, SZ Cyg, SS CMa, XY Car, S Vul, X Pup and WZ Sgr). These data will improve the precision of the final parallaxes by identifying and eliminating binaries among ther eference stars, providing a longer baselien for proper motion determination, and providing direct overlap with Gaia observations.

GO 14709: HST/WFC3 Spectroscopy of < 400 AU Companions to Orion Young Stellar Objects


An image of the Orion Nebula superimposed on the 13CO map of Orion A (from this link ).
The Orion association is the largest nearby star-forming complex, providing a key laboratory for unlocking the secrets of star formation. As such, it has been subject to intense scrutiny at all wavelengths from both ground and space. Surveys at near-infrared and mid-infrared wavelenths, notably by Spitzer, have identified an extensive number of embedded sources, young stellar objects (YSOs) that are still accreting from the surrounding molecular gas. A follow-up HST proposal focused on more than 250 sources within the Orion A molecular cloud, the complex that includes the Orion Nebula Cluster. Initially,NICMOS was used to survey a subset of the protostars; following SM4, the WFC3-IR camera was applied to the task. The observations provided an excellent complement to Spitzer since, while HST cannot offer either the same areal coverage or sensitivity at mid-infrared wavelegths, HST gives a resolution close to 0.1 arcsecond, an order of magnitude higher than the Spitzer images. That program resulted in the detection of several very faint companions, with luminosities consistent with planetary mass (5 MJ) objects. The present program is using the G141 grism on WFC3-IR to obtain spectra and determine the true nature of these objects with the overall goal of constraining the mass function of sub-stellar-mass companions.

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