This week on HST


HST Programs: December 26, 2011 - January 1, 2012


Program Number Principal Investigator Program Title
12025 James C. Green, University of Colorado at Boulder COS-GTO: QSO Absorbers, Galaxies and Large-scale Structures in the Local Universe Part 2
12041 James C. Green, University of Colorado at Boulder COS-GTO: Io Atmosphere/STIS
12062 Sandra M. Faber, University of California - Santa Cruz Galaxy Assembly and the Evolution of Structure over the First Third of Cosmic Time - III
12067 Marc Postman, Space Telescope Science Institute Through a Lens, Darkly - New Constraints on the Fundamental Components of the Cosmos
12072 Julianne Dalcanton, University of Washington A Panchromatic Hubble Andromeda Treasury - I
12073 Julianne Dalcanton, University of Washington A Panchromatic Hubble Andromeda Treasury - I
12076 Julianne Dalcanton, University of Washington A Panchromatic Hubble Andromeda Treasury - I
12105 Julianne Dalcanton, University of Washington A Panchromatic Hubble Andromeda Treasury - I
12107 Julianne Dalcanton, University of Washington A Panchromatic Hubble Andromeda Treasury - I
12187 Luis C. Ho, Carnegie Institution of Washington A New Sample of Circumnuclear Gas Disks for Measuring Black Hole Masses in Spiral Galaxies
12273 Roeland P. van der Marel, Space Telescope Science Institute Mass of the Local Group from Proper Motions of Distant Dwarf Galaxies
12440 Sandra M. Faber, University of California - Santa Cruz Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey -- GOODS-South Field, Non-SNe-Searched Visits
12463 Heidi B. Hammel, Space Science Institute Target of Opportunity Imaging of an Unusual Cloud Feature on Uranus
12472 Claus Leitherer, Space Telescope Science Institute CCC - The Cosmic Carbon Conundrum
12474 Boris T. Gaensicke, The University of Warwick The frequency and chemical composition of rocky planetary debris around young white dwarfs
12476 Kem Cook, Eureka Scientific Inc. Measuring the Hubble Flow Hubble Constant
12488 Mattia Negrello, Open University SNAPshot observations of gravitational lens systems discovered via wide-field Herschel imaging
12502 Andrew S. Fruchter, Space Telescope Science Institute From the Locations to the Origins of Short Gamma-Ray Bursts
12531 Alex V. Filippenko, University of California - Berkeley Tracking the Continuing Evolution of SN 1993J with COS and WFC3
12543 Robert H. Rubin, NASA Ames Research Center Fine-scale Density, Temperature, and Ionization Fluctuations: Their Effect on Abundance Determinations
12546 R. Brent Tully, University of Hawaii The Geometry and Kinematics of the Local Volume
12550 Daniel Apai, University of Arizona Physics and Chemistry of Condensate Clouds across the L/T Transition - A SNAP Spectral Mapping Survey
12592 Ryan Foley, Smithsonian Institution Astrophysical Observatory Understanding the Progenitor Systems, Explosion Mechanisms, and Cosmological Utility of Type Ia Supernovae
12603 Timothy M. Heckman, The Johns Hopkins University Understanding the Gas Cycle in Galaxies: Probing the Circumgalactic Medium
12613 Knud Jahnke, Max-Planck-Institut fur Astronomie, Heidelberg Are major galaxy mergers a significant mechanism to trigger massive black hole growth at z=2?
12658 John M. Cannon, Macalester College Fundamental Parameters of the SHIELD Galaxies
12785 Roberta M. Humphreys, University of Minnesota - Twin Cities The Strange Supernova or Supernova Impostor SN2011ht

Selected highlights

GO 12072: A Panchromatic Hubble Andromeda Treasury


M31: the Andromeda spiral galaxy
M31, the Andromeda galaxy, is the nearest large spiral system to the Milky Way (d ~ 700 kpc), and, with the Milky Way, dominates the Local Group. The two galaxies are relatively similar, with M31 likely the larger system; thus, Andromeda provides the best opportunity for a comparative assessment of the structural properties of the Milky Way. Moreover, while M31 is (obviously) more distant, our external vantage point can provide crucial global information that complements the detailed data that we can acquire on individual members of the stellar populations of the Milky Way. With the advent on the ACS and, within the last 2 years, WFC3 on HST, it has become possible to resolve main sequence late-F and G dwarfs, permitting observations that extend to sub-solar masses in M31's halo and disk. Initially, most attention focused on the extended halo of M31 (eg the Cycle 15 program GO 10816 ), with deep imaging within a limited number of fields revealing the complex metallicity structure within that population. With the initiation of the present Multi-Cycle Treasury program, attention switches to the M31 disk. "PHAT" will conduct a multi-waveband survey of approximately one third of disk and bulge, focusing on the north-east quadrant. Observations will extend over the next three cycles, and will provide a thorough census of upper main-sequence stars and star forming regions, matching the stellar distribution against the dust and gas distribution.
GO 12273: Mass of the Local Group from Proper Motions of Distant Dwarf Galaxie


The dwarf galaxy, Leo A, as imaged by the Subaru telescope
M31 and the Milky Way are the two largest members of the Local Group, with masses of ~4 x 1011 and ~1011 MSun, respectively. As such, they dominate the system dynamics; M33 and the LMC are the next largest systems, with masses lower by a factor of 10. Radial velocity measurement show that M31 and the Milky Way are converging at a velocity of ~125 km/sec; however, interpreting that result in cosmological terms requires a better understanding of the total mass of the Local Group. Using a variety of techniques, current estimates range over a factor of 5, from ~1.3 x 1012 MSun to ~5.6 x 1012 MSun. T%he present program aims to apply stronger constraints to this fundamental value by measuring proper motions for four dwarf galaxies that lie towards the edge of the local group: Cetus, Leo A, Tucana and the Sagittarius Dwarf Irregular. First epoch observations with the ACS/WFC are already available in the archive for these four systems. The present program will build on those, obtaining new I-band (F814W) observations with the ACS/WFC, while simulateously using the WFC3-UVIS camera in parallel to obtain deep B (F475W) and I (F814W) colour-magnitude data for these low-mass systems.

GO 12476: Measuring the Hubble Flow Constant


NGC 4911, from DSS scans of POSS II IIIaJ plate material
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 and the extragalactic distance scale figure largely in HST's history, notably through the Hubble Constant Program, one of the initial Key Projects. Hubble has accumulated WFPC2 and NICMOS observations of Cepheids in 31 galaxies. All of those galaxies lie within 25 Mpc; thus, both the Key Project's derivation of H0 = 72 +/- 8 km/sec/Mpc and the competing value, H0 = 56 +/- 7 km/sec/Mpc, (an offset of 1.5 sigma), rely on secondary indicators to take measurements to the far-field Hubble flow. The aim of the present project is to extend covrage to Cepheids within the Coma cluster. The program had its genesis in a Cycle 15 Treasury program that was designed to use the high sensitivity and high resolution of the Adnaced camera for Surveys to search for Cepheids in two spiral galaxies in the cluster, NGC 4911 and NGC 4921. If Coma lies at a distance of 100 Mpc ( (m-M)=35.0), then long-period Cepheids (P~50 days) have mean apparent magnitudes of V~29 - challenging observations even for ACS. Unfortunately, the ACS failure in January 2007 left the original program barely 40% complete. However, the initial dataset was sufficient to identify 50 long-period Cepheids candidates in NGC 8921. The present program aims to build on those incomplete results by using the UVIS channel on Wide-field Camera 3 to obtain cadenced observations in the F350LP and F606W filters, and determine periods for verified variable stars..

GO 12550: Physics and Chemistry of Condensate Clouds across the L/T Transition - A SNAP Spectral Mapping Survey


Brown dwarfs are likely to have complex atmospheric structures that resemble Jupiter
Brown dwarfs are failed stars - objects that form like stars, by gravitational collapse within giant molecular clouds, but which have insufficient mass to raise the central temperature above 107 K, and which therefore are unable to ignite hydrogran fusion and maintain a long-lived central energy source. As such, these objects reach a maximum surface temperature of perhaps 3,000K some tens of millions of years after their formation, and subsequently cool and fade into oblivion. As they cool, they move through spectral types M, L and T, with the oldest brown dwarfs now likely to have temperatures close to 300K and emergent spectra characterised by water and ammonia bands, the putative signatures of the spectral class Y. As these dwarfs cool from L to T (~1500 to ~1200K), the atmospheres undergo significant changes, with heavier elements condensing to form dust. That dust can form clouds, perhaps giving the dwarf's surface a banded appearance, similar to Jupiter. or leading to the generation of localised cloud features. Since the rotation periods for these obejcts are usually a matter of a few hours, the appearance and disappearance of asymmetric features might lead to periodic photometric or spectroscopic variability, and at least photometric variability has been detected for a handful of ultracool dwarfs. The clouds themselves may appear and disappear over relatively short timescales, leading to longer-term photometric variations at particular wavelengths. A Cycle 18 program (GO 12314) focuses on a handful of brown dwarfs near the L/T transition, using the WFC3 grism to obtain multi-orbit, high-accuracy monitoring of their spectral behaviour. That program succeeded in recovering significant variability, with periods from 5-10 hours. The present program builds on those results by extending coverage to a much larger sample of late-L/early-T dwarfs. As a SNAP prorgam, each will be observed for only ~40 minutes. insufficient to determine periodicities, but, given the high precision of HST, sufficient to identify new candidates and gain some insight into the frequenciy of the phenomenon.

Past weeks:
page by Neill Reid, updated 8/12/2011