This week on HST


HST Programs: October 22 - October 28, 2012

Program Number Principal Investigator Program Title
11622 Heather A. Knutson, California Institute of Technology A Search for Water and Methane on a Neptune-Mass Transiting Planet
12458 Marc Postman, Space Telescope Science Institute Through a Lens, Darkly - New Constraints on the Fundamental Components of the Cosmos
12465 Paul A. Crowther, University of Sheffield A Massive Star Census of the Starburst Cluster R136
12477 Fredrick W. High, University of Chicago Weak lensing masses of the highest redshift galaxy clusters from the South Pole Telescope SZ survey
12525 William C. Keel, University of Alabama Giant Ionized Clouds Around Local AGN - Obscuration and History
12559 Justyn R. Maund, University of Copenhagen, Niels Bohr Institute Stellar Forensics III: A post-explosion view of the progenitors of core-collapse supernovae
12567 Thomas R. Ayres, University of Colorado at Boulder Bridging STIS's Neutral Density Desert
12581 Julia Christine Roman-Duval, Space Telescope Science Institute - ESA A Direct CO/H2 Abundance Measurement in Diffuse and Translucent LMC and SMC Molecular Clouds
12586 Kailash C. Sahu, Space Telescope Science Institute Detecting and Measuring the Masses of Isolated Black Holes and Neutron Stars through Astrometric Microlensing
12604 Andrew J. Fox, Space Telescope Science Institute - ESA Ionization in the Magellanic Stream: A Case Study of Galactic Accretion
12605 Giampaolo Piotto, Universita degli Studi di Padova Advances in Understanding Multiple Stellar Generations in Globular Clusters
12661 Michael C. Liu, University of Hawaii Dynamical Masses of the Coolest Brown Dwarfs
12669 Luigi R. Bedin, Osservatorio Astronomico di Padova Exploring the Bottom End of the White Dwarf Cooling Sequence in the Open Cluster NGC6819
12812 Zolt Levay, Space Telescope Science Institute Hubble Heritage
12813 Brian Schmidt, Australian National University Network of 13 high precision STIS spectrophotometric standards for ground based surveys
12866 Mark Swinbank, University of Durham A Morphological Study of ALMA Identified Sub-mm Galaxies with HST/WFC3
12873 Beth Biller, Max-Planck-Institut fur Astronomie, Heidelberg Search for Planetary Mass Companions around the Coolest Brown Dwarfs
12879 Adam Riess, The Johns Hopkins University A 1% Measurement of the Distance Scale with Perpendicular Spatial Scanning
12889 Sherry H. Suyu, Academia Sinica, Institute of Astronomy and Astrophysics Accurate Cosmology from Gravitational Lens Time Delays
12891 Keith S. Noll, NASA Goddard Space Flight Center Search For Binaries Among Ultra-Slow Rotating Trojans, Hildas, and Outer Main Belt Asteroids
12893 Ronald L Gilliland, The Pennsylvania State University Study of Small and Cool Kepler Planet Candidates with High Resolution Imaging
12903 Luis C. Ho, Carnegie Institution of Washington The Evolutionary Link Between Type 2 and Type 1 Quasars
12927 Andrew B. Newman, California Institute of Technology The role of the environment in the growth of compact red galaxies at z~2
12929 Judith L. Provencal, University of Delaware COS Observations of Pulsating DB White Dwarfs
12966 Roeland P. van der Marel, Space Telescope Science Institute The Nature of Dark Matter: Halo Cusps or Cores from dSph internal proper motion dynamics
12993 Jose Luis Prieto, Princeton University The Stellar Environment of SN 2008jb: Resolving the Nature of the Progenitor
12995 Christopher Johns-Krull, Rice University Testing Disk Locking in the Orion Nebula Cluster
12999 Ryan Foley, Smithsonian Institution Astrophysical Observatory Are the Progenitors of SN 2002cx-like Objects Massive Stars or White Dwarfs?
13010 Fabio Bresolin, University of Hawaii A precise calibration of the zero point of the cosmic distance scale from late-type eclipsing binaries in the LMC
13012 Laurent Lamy, Observatoire de Paris - Section de Meudon Near-equinox spectro-imaging of Uranus aurorae sampling two planetary rotations

Selected highlights

GO 11622: A Search for Water and Methane on a Neptune-Mass Transiting Planet


Artist's impression of the exo-Neptune in orbit around Gliese 436
Gliese 436 is an early-type M dwarf (spectral type M2.5) with a mass approximately 40% that of the Sun lying at a distance of ~10 parsecs. In August 2004, the Lick/Carnegie planet search team (led by Geoff Marcy and Paul Butler) announced the discovery of a ~22 Earth-mass planet in a 2.64 day orbit around this star. Unlike most "hot jupiters", this "hot Neptune" is on an elliptical orbit, e=0.16, which, with a semi-major axis of 0.0278 AU, brings it within 3.5 million kilometres of the central star. Gl 436 is significantly cooler than the Sun, with a surface temperature close to ~3400 degrees Kelvin; even so, the "surface" temperatures on Gl 436b are expected to reach ~740 K (~370 C). In May of this year, a team led by F. Pont demonstrated that Gl 436b transits the parent star. The initial ground-based observations allowed them to derive a diameter approximately 4 times that of Earth, directly comparable with Uranus and Neptune. This provides key insight into the likely origins of Gl 436b, since combining the diameter with the measured mass gives the mean density, and, by inference, the likely composition. For Gl 436b, the indications are that the planet is a displaced "ice giant". Subsequent observations with HST (eg GO 11306) have refined the radius determination. The present program aims to probe the atmospheric structure by using drift-scanning to obtain high signal-to-noise spectra with the WFC3-IR G141 grism. The spectral regions covered (1.3 to 1.7 microns) span several strong absorption bands due to water and methane; differencing the spectra when the system is in and out of transit may lead to detection of significnt atmospheric absorption.

GO 12873: Search for Planetary Mass Companions around the Coolest Brown Dwarfs


NICMOS images of the ultracool L/T binary, 2MASS J22521073-1730134; the northern component, notably fainter at F160W, is the T dwarf.
Brown dwarfs are objects that form like stars, but lack sufficient mass to drive the central temperature above a few million degrees, and therefore never succeed in igniting core hydrogen fusion. Discovered almost 15 years ago, these objects initially have surface temperatures of ~3,500K, but cool rapidly and move through spectral types M, L and T. Following their discovery, considerable theoretical attention has focused on the evolution of their intrinsic properties, particularly the details of the atmospheric changes in the evolution from type L to type T and beyond. This transition marks the emergence of methane as a dominant absorber at near-infrared wavelengths. Current models suggest this transition occurs at ~1400-1200K, and that the spectral changes are at least correlated with, and perhaps driven by, the distribution and properties of dust layers ("clouds"). The overall timescales associated with this process remain unclear. Recent discoveries from both wide-field ground-based surveys (such as UKIDDS, on the UK infrared Telescope) and from space (notably by WISE, the Wide-field Infrared Survey Explorer) have resulted in the detection of significant numbers of extremely cool T dwarfs, and, indeed, a handful of dwarfs beyond T, reaching spectra type Y. Identifying even cooler systems in the field is extremely challenging, due to their extremely low luminosities. However, since around 15-20% of low-mass brown dwarfs appear to be binary (at least among spectral classes L and T), the known systems offer potential search locations for cooler, lower-mass companions. The present program is using imagign with the WFC3-IR camera in the F127M and F138M filters to search for such systems among 34 recently discovered very cool (>78) brownd warfs.

GO 12999: Are the Progenitors of SN 2002cx-like Objects Massive Stars or White Dwarfs?


The discovery image of the August 2011 SNe in M101
Supernovae are the most spectacular form of stellar obituary. Since B2FH, the physical processes underlying their eruptive deaths have been known to play a key role in populating the ISM with metals beyond the iron peak. More recently, these celestial explosions have acquired even greater significance through the use of Type Ia supernovae as distance indicators in mapping the `dark energy' acceleration term of cosmic expansion. However, while there are well-established models for the two main types of supernovae (runaway fusion on the surface of a white dwarf in a binary system for Type Ia, or detonation of the core in Type II), some significant uncertainties remain concerning the physical details of the disruption, and, potentially, the overall uniformity of these events. Consequently, there is potential for systematic bias in the distance estimates. In particular, a subset of supernovae have light-curves that are superficially similar i morphoogy to type Ia, but which can decline at significantly different rates and appear to have substantially lower maximum luminosities. Classed as type Ia peculiar, SN 2002cx is the prototype of a subset of these objects. It is not clear whether these are the product of core collapse within a massive star, or partial deflagration of a white dwarf. The present program aims to address this issue by using deep, high spatial resolution HST observations with tha Advance Camera for Surveys to probe the stellar population in the immediate vicinity of four recent supernovae of this class: SN 2008ge, SN2008ha, SN 2010ae and SN2010el. Should these systems all lie close to regions with on-going star formation, then this may argue in favour of their origin in young, massive stars; location in quiescent inter-arm regions would favour the (evolevd) whtie dwarf origin.

GO 13012: Near-equinox spectro-imaging of Uranus aurorae sampling two planetary rotation


Nicmos image of aurorae on Uranus
The atmospheres of the gas giant planets in the solar system are dynamic entities that can exhibit dramatic changes over a variety of timescales. In addition to changes within the atmospheres themselves, due the formation and dissipation of storms, these systems can exhibit auroral activity. Planetary aurorae are stimulated by the influx of charged particles from the Sun, which travel along magnetic field lines and funnel into the atmosphere near the magnetic poles. Aurorae therefore require that a planet has both a substantial atmosphere and a magnetic field. Aururae are common phenomena on Earth, sometimes visible at magnetic latitudes more than 40 degrees from the pole, and have also been seen on Jupiter, Saturn, Uranus and Neptune.The Uranian aurorae are less intense, and were first detected by Voyager 2 during its flyby in 1986. At that time, Uranus was oriented almost pole-on to Earth, allowing observations of only one hemisphere. Now, 25 years later, Uranus has completed more than a quarter of its 84-year-period orbit, and passed through the equator-on ring plane crossing in late 2007 (see Program GO 10870 ). . As a result, we now have clear access to both the northern and southern polar regions. The peresent observing program aims to capitalise on that by targeting Uranus for observation close to its 2012 opposition, and using the Space Telescope Imaging Spectrograph (STIS) and the Advanced Camera for Surveys Solar Blind Channel (ACS/SBC) to obtain spectra and ultraviolet imaging of the planet. The goal is to trace the evolution of active phenomena structures over a full diurnal rotation period.

Past weeks:
page by Neill Reid, updated 14/10/2012
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