This week on HST


HST Programs: November 11 - November 17, 2013

Program Number Principal Investigator Program Title
12880 Adam Riess, The Johns Hopkins University The Hubble Constant: Completing HST's Legacy with WFC3
12909 John Henry Debes, Space Telescope Science Institute WFC3 Micro-arcsecond astrometry of the possible SNIa progenitor BPM 71214
12970 Michael C. Cushing, University of Toledo Completing the Census of Ultracool Brown Dwarfs in the Solar Neighborhood using HST/WFC3
13000 Sungryong Hong, National Optical Astronomy Observatory, AURA Impact of Environments on Lyman alpha Emitting Galaxies at High Redshift {z ~ 2.7}
13011 Thomas H. Puzia, Pontificia Universidad Catolica de Chile Searching for the H-alpha 'Smoking Gun' of Prolonged Star Cluster Formation
13046 Robert P. Kirshner, Harvard University RAISIN: Tracers of cosmic expansion with SN IA in the IR
13113 C. S. Kochanek, The Ohio State University ENERGY DEPENDENT X-RAY MICROLENSING AND THE STRUCTURE OF QUASARS
13295 Soeren S. Larsen, Radboud Universiteit Nijmegen Do the globular clusters in the Fornax dSph have multiple stellar populations?
13302 J. Michael Shull, University of Colorado at Boulder COS Spectra of High-Redshift AGN: Probing Deep into the Rest-Frame Ionizing Continuum and Broad Emission Lines
13305 Carolin Villforth, University of St. Andrews Do mergers matter? Testing AGN triggering mechanisms from Seyferts to Quasars
13324 Davor Krajnovic, Astrophysikalisches Institut Potsdam Where cores are no more: assessing the role of dissipation in the assembly of early-type galaxies
13326 Ragnhild Lunnan, Harvard University Zooming In on the Progenitors of Ultra-Luminous Supernovae with HST
13332 Seth Redfield, Wesleyan University A SNAP Survey of the Local Interstellar Medium: New NUV Observations of Stars with Archived FUV Observations
13344 Adam Riess, The Johns Hopkins University A 1% Measurement of the Distance Scale with Perpendicular Spatial Scanning
13350 Andrew S. Fruchter, Space Telescope Science Institute How Low Can They Go? Detecting low luminosity supernova progenitors
13380 Michael Nowak, Massachusetts Institute of Technology Probing Black Hole Disk Atmospheres with EPIC and RGS Observations of 4U 1957+11
13389 Brian Siana, University of California - Riverside The Ultraviolet Frontier: Completing the Census of Star Formation at Its Peak Epoch
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
13445 Joshua S. Bloom, University of California - Berkeley Absolute Calibration of the Extragalactic Mira Period-Luminosity Relation
13467 Jacob L. Bean, University of Chicago Follow The Water: The Ultimate WFC3 Exoplanet Atmosphere Survey
13481 Emily Levesque, University of Colorado at Boulder Calibrating Multi-Wavelength Metallicity Diagnostics for Star-Forming Galaxies
13490 Jason A. Surace, California Institute of Technology Resolving the Reddest Extragalactic Sources Discovered by Spitzer: Strange Dust-Enshrouded Objects at z~2-3?
13495 Jennifer Lotz, Space Telescope Science Institute HST Frontier Fields - Observations of Abell 2744
13609 David Jewitt, University of California - Los Angeles Investigating the Trigger Mechanism for Newly Discovered Main Belt Comet P/2013 P5
13611 Nial R. Tanvir, University of Leicester The nature of the low redshift ultra-long GRB130925A: core collapse or tidal disruption?
13612 David Jewitt, University of California - Los Angeles Hubble Investigation of the First Known, Multi-Fragment Main Belt Comet: P/2013 R3

Selected highlights

GO 12880: The Hubble Constant: Completing HST's Legacy with WFC3


NGC 7541 (upper left), one of the spiral galaxies targeted in this program
The Hubble constant remains a key parameter in understanding cosmology and the evolution of the Universe. Refining measurements of H0 therefore still represents a vital means of probing the nature of dark energy. The present program aims to tackle this question by laying a firmer foundation to the SNe Ia distance scale. The WFC3 IR camera will be used to identify and characterise Cepheid variables in eight relatively nearby galaxies that have hosted Type Ia SNe. Cepheids have signficantly lower amplitude at near-infrared wavelengths, and the measured magnitudes are less subject to uncertainties due to foreground reddening and variations in metallicity. As a consequence, determining the mean apparent magnitude, and hence the period/apparent magnitude relation, is substantially more straightforward than at optical wavelengths. WFC3 has revolutionised this field by providing substantial greater areal coverage and higher precision photometry than NICMOS. Past observational program have targeted the Cepheids in the maser galaxy, NGC 4258, as well as Galactic Cepheids. The present program targets eight galaxies that have hosted Type Ia supernovae, offering the prospect of tying the SNe Ia scale directly to the Galaxy and to NGC 4258, avoiding the many intermediate steps of previous analyses. The aim is to reduce the level of systematics in determinations of H0 to the 1-2 percent level, setting signficantly stronger constraints on dark energy.

GO 13332: A SNAPSHOT Survey of the Local Interstellar Medium: New NUV Observations of Stars with Archived FUV Observation

A map of the Local Stellar Neighbourhood Understanding the nature and structure of gas within the interstellar medium is a key step towards understanding how material is recycled and how energetic processes, such as stellar winds and outflows, feed energy into the overall system. UV spectroscopy plays a key role in probing these effects: hot, background objects that produce relatively few intrinsic absorption features serve to map the the velocities and temperatures within the intervening gas along the line of sight. Observations of quasars are used to probe galaxy halos at moderate and high redshift; observations of hot stars provide similar information for gas in the Milky Way. The present program is using STIS to target stars within 100 parsecs of the Sun, studying the nearby interstellar medium. All of these stars have prior observations at far-UV wavelengths; the STIS data will cover the near-UV, surveying Fe II and Mg II absorption.This program builds on observations spanning 36 targets from Cycle 17.

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.

GO 13612: Hubble Investigation of the First Known, Multi-Fragment Main Belt Comet: P/2013 R3


MBC P/2013 P5 as imaged by Hubble in September
The term 'comet" is generally associated with low-mass, volatile-rich solar system objects that spend most of their life at very lage distances from the Sun, plunging only rarely into the inner regions where they acquire extended tails due to outgassing. Sometimes those obejcts are captured into short-period, eccentric orbits, leading to rapid depletion of the volatile content in rapidly-successive perihelion passages. However, recent years have seen growing evidence of another class of cometes exist: comets with near-circular orbits that place them between Mars and Jupiter, within the realm of the Main Belt of asteroids. One of the first candidate main belt comets, as these objects have been dubbed, is the asteroid Scheila. Discovered by the Heidelberg astronomer August Kopff in 1906, and named after an English student with whom he was acquainted, this is one of the larger known asteroids, with a diameter estimated as ~110 km. Early December 2010, Steve Larson (of Arizona's Lunar and Planetary Laboratory) noted that Scheila had sprouted a coma halo in observations taken by the Catalina Sky Survey. An examination of archival images revealed no evidence for activity throughout October and November, but a possible onset on December 3rd. The asteroid 1979 OW7/1996 N2 exhibited similar behaviour in 1996 and again in 2002; the initial outburst was ascribed to a collision, but the second event suggests that the activity is intrinsic rather than externally stimulated. More recently, the Pan-STARRS survey has contributed several objects, including the asteroid 2006 VW139, imaged during an outburst, MBC 2013-P5, which has exhibited a spectacular set of dusty tails, and MBC P/2013 R3, which shows clear evidence for multiple "nuclei". The present HST program will use high-resolution visual imaging with Wide-Feld Camera 3 to probe the detailed nature of the this object.

Past weeks:
page by Neill Reid, updated 14/10/2013
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