ASTRONOMY DEPARTMENT

Stella Kafka, IPAC

"Magnetic Activity on Cataclysmic Variable Secondaries: Nature or Nurture?"

Chromspheric Activity on the mass-losing secondary star in cataclysmic variables (CVs) is commonly invoked to explain sustained mass transfer 
caused by system angular momentum loss via a magnetized stellar wind.  Such activity may also be responsible for the CV period gap, and for 
the widely differing mass transfer rates among CVs at the same orbital period. However, there is a substantial lack of observational support 
for these scenarios, because conventional activity indicators (such as X-rays, H-alpha emission, and flares) can also be produced by accretion. 
Here we present an extended spectroscopic monitoring campaign of a few magnetic CVs at times of reduced accretion. Unusual structures in the 
H-alpha line reveals magnetically confined gas motions in large, long-lived loop prominence-like structures on the donor star. This is the first 
direct observational evidence of such activity leading to a few surprises on its formation and a new paradigm on magnetic activity in CVs.

John Johnson, University of Hawaii, Honolulu

"Planet Hunting In New Stellar Domains"

    
    I will present the recent results from our search for planets orbiting massive
subgiants. The decreased rotation rates and cooler surface temperatures of
these "retired" A-type stars make them ideal proxies for their massive
(1.5 to 2 solar-mass) main-sequence progenitors. Our results indicate that
A stars such as Sirius are significantly more likely than Sun-like stars to have
a Jupiter-sized planet, which confirms one of the predictions of the core
accretion theory of planet formation. Also, the collection of 9 planets detected
from our sample displays a puzzling lack of semimajor axes smaller than 1 AU,
a finding that will likely have important implications for the various theories of
planet migration. 

Thr  Apr 17
4:00 A102

Dan Lester, University of Texas

"Telescopes Up On the Rocks? A Reevaluation of the Moon as a Site for Astronomy"

The lunar surface has been classically assumed to be an enabling site for astronomical telescopes. The new Vision for Space Exploration, which would take us back to the surface of the Moon by the end of the next decade and eventually develop a continuously crewed outpost that would anchor our efforts there, prompts a review of this assumption. In general, while originally valuable to astronomical observatories, such siting is now found to be quite inferior to free space. This change of science strategy is the result of advances in both technology and space operations management in the last decade. While the Moon can be seen as a stable platform to support a telescope, we have now mastered pointing and tracking technology in free space. In addition, the lunar surface is actually disadvantageous in terms of power availability, thermal, optical alignment, and contamination control. Although the Moon itself seems to be non-optimal for most astronomical telescopes, the hardware being developed to get there appears to be profoundly enabling for astronomy. This Constellation architecture offers new opportunities for space science off the lunar surface that are now just being considered.

Thr   Apr 24 4:00 A102

Kim Venn, University of Victoria

"Where and What are the First Stars?"

First stars are those with zero initial metallicities, and are thought to have started to form at z>10, and continuing thereafter, with a peak z~5-6. Today, searches for first stars equates to searches for the most metal-poor stars in the Galactic halo. However, are either of these assumptions correct? Several of the most metal-poor stars in the solar neighborhood have later proven to be chemically peculiar stars, and I will show that the two stars currently thought to be first stars also have some of these features. Furthermore, is the Galactic halo really the place to find first stars? Most galaxy formation models suggest first stars formed in the bulge, not in the halo, as well as in dwarf galaxies. Large aperture telescopes now make it possible to search the dwarf galaxies themselves, and I will present some of these results.

Thr May 1

4:00 A102

Sumner Starrfield, Arizona State University

"The RS Oph Outburst in 2006: A Hot Flash on a Degenerate Dwarf"  

RS Oph was observed in outburst on February 12, 2006 and, for at least the fifth time in recorded history, reached naked eye visibility.  RS Oph is a member of a class of stars called recurrent novae because their outbursts have been detected more than once.  We jumped at the opportunity to observe this system both with the large number of satellites now in orbit and ground-based facilities that had far superior detectors to those available for its last outburst in January 1985.  This system has a white dwarf (probably massive) in a 455 day orbit around a cool giant.  The giant is transferring hydrogen rich matter onto the white dwarf at a rate that is sufficient for an explosion every 20 years or so.  In contrast, a classical nova binary system also contains a white dwarf star but the mass losing star is a low mass star (like the sun) in a few hour orbit around the white dwarf and the time between explosions may be as long as 100,000 years or more. I will report on the unprecedented data that we obtained with X-ray satellites such as Chandra and Swift plus discuss the possible relationship between RS Oph and Supernovae of Type Ia.  These latter explosions are thought responsible for the iron group elements in the Solar System and are now being used to study the evolution of the Universe.

Thr May 8
4:00 A102

Paul Green, CfA/Harvard

" X-raying Pandora’s Box with the ChaMP "

The ongoing Chandra Multiwavelength Project is a large, archival survey of serendipitous sources in the X-ray sky at high Galactic latitude.   X-ray observations play a key role in unveiling active galactic nuclei (AGN), because most extragalactic X-ray sources are AGN, and vice versa.  I will describe recent ChaMP results on the X-ray luminosity function of quasars, but also on nearby galaxies, and galaxy groups and clusters.  These studies take advantage of Chandra's excellent spatial resolution and sensitivity, leveraged by our own deep imaging, and spectroscopy.  We also describe the extended ChaMP, encompassing 323 Chandra fields with SDSS overlap, from which we constrain the spectral energy distributions of a thousand broad line QSOs and outline other ongoing projects, including a study of stellar coronal emission.

Thr May 15

4:00 A102

Mate Adamkovics, University of California, Berkeley

"Condensed-phase methane and tropospheric meteorology on Titan (Part I)"

The largest moon of Saturn is enshrouded by aerosol hazes, making the lower atmosphere and solid surface difficult to study. Recent advances in IR instrumentation, adaptive optics, and the Cassini/Huygens mission have produced numerous, sometimes difficult to reconcile, views of this environment. I will describe how a significant discrepancy between near infrared observations and radiative transfer models can be resolved by a rudimentary treatment of large methane droplets or solid methane particles in Titan's atmosphere. I will present measurements from ground-based VLT/SINFONI and  Keck/OSIRIS instruments, as well as the Cassini/VIMS spacecraft, while explaining a technique for enhancing contrast in haze-obscured and surface-contaminated images of the lower atmosphere. Views of changing global-scale hazes, cloud evolution, and indications of precipitation will be discussed in the context of past predictions that have been confirmed (or refuted) by new observations.  (Part II of Condensed-phase methane and tropospheric meteorology on Titan will be presented the following day in Atmopsheric Sciences' weekly colloquium.)

Thr May 22

4:00 A102

Crystal Brogan, University of Florida

"Igniting the Galaxy: investigating star formation in global models of disk galaxies"

Thr May 29

4:00 A102

Jacqueline van Gorkom, Columbia University

"The Evolution of Galaxies in Different Environments"

In the densest parts of clusters the morphological mix and colors of galaxies is very different from galaxy properties in lower density regions. More recent evidence indicates that these properties change very smoothly from the cluster core out to several megaparsecs. I will focus on the fate of the gas in galaxies in these environments. When and where do galaxies stop accreting gas, how do they loose the gaseous reservoir, when does star formation stop? I will argue that it is the assembly of clusters that may affect the evolution of the galaxies.