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University of Wyoming

University of Wyoming Physics & Astronomy Colloquium Series

Fridays -- 4:10 PM -- Prowse Room 234

Pre-Colloquium tea served at 3:45 in the Cinnamon Room, PS 237

Spring 2008 Schedule

Feb 1 Pablo Bauleo (Colorado State)
Recent Results and Status of The Pierre Auger Cosmic Ray Observatory

Abstract: The Pierre Auger Collaboration goal is to measure the upper end of the cosmic ray spectrum (E > 10^19 eV) using two observatories, one located in Argentina -under construction- and the other one in Colorado -under planning-. At those energies the flux is extremelly low (1 CR/km**2/year) therefore each observatory will cover an area larger than 3.000 km**2, both in the Argentinean pampas and in the high plains of southeast Colorado. There is not a conclusive model that can explain how the particles could be accelerated at those energies but recent experimental data has begun to shine light on the cosmic ray sources location. At the highest energies the arrival directions correlates with the spatial distribution of AGNs. This talk will cover the measurement techniques, the observatory status, summarize the recent released results obtained with the southern detector as well as cover future research plans and status of the northern observatory.

Feb 22 Srikanth Hariharan (U. South Florida)
Functional Magnetic Nanostructures: Living on the Edge

Magnetic nanostructures are considered basic building blocks in spintronics and high-density data storage applications. Surface and configurational effects in oxide nanoparticle assemblies have been increasingly found to play significant roles in controlling the magnetic anisotropy. Surface terminations in ferrite nanoparticles, core-shell structures and composite metal-oxide nanostructures that favor spin frustration can contribute to significant enhancement of anisotropy. For instance, these effects could result in tunable exchange bias which is useful in overcoming the superparamagnetic limit and enhancement of the magnetic entropy potentially useful for spot cooling in MEMS/NEMS devices. Surface contributions to magnetic anisotropy are notoriously difficult to probe using conventional magnetization experiments. Over the years, we have pioneered the sensitive method of radio-frequency (RF) transverse susceptibility that is unique in terms of its ability to precisely probe such phenomena. We will present and discuss novel cooperative magnetic phenomena arising from surface and interface effects as probed by AC and RF dynamic susceptibility experiments in nanoscale oxides as well as thin film heterostructures. Overall, we demonstrate that RF susceptibility experiments are ideally suited to sensitively probe novel magnetic phenomena in oxide nanostructures and heterostructures. Work supported by the DOE-BES, NSF and ARO.

Mar 14 John Feldmeier (Youngstown State U.)

April 18 Jennifer Hoffman (University of Denver)
Polarization of circumstellar material across the HR diagram

Stars do not evolve in isolation, but rather interact with their surroundings in a variety of ways throughout their lifetimes. Configurations of gas such as disks, winds, jets, and outflows mediate between stars and their local environments, from the youngest accreting prestellar systems to the most spectacular supernova explosions. Using examples from various stages of stellar evolution, I will discuss the ways astronomers can study these interactions by using polarimetric observations and numerical modeling to probe the geometrical and optical characteristics of circumstellar matter distributions.

April 25 Cynthia Froning (Colorado)
Near-Infrared Spectroscopy of Compact Binaries: Structure, Evolution, and Black Hole Masses

Compact binaries are interacting binary systems in which a late-type donor star fills its Roche lobe and transfers mass to a compact accretor. When the accreting object is a white dwarf, the systems are called cataclysmic variables; when the accretor is a black hole or a neutron star, they are designated X-ray binaries. Compact binaries are excellent test beds for investigations of the physics of accretion, binary stellar evolution, relativistic effects, thermonuclear bursts, and outflows from winds and collimated jets. In this talk, I will present the results of near-infrared photometry and spectroscopy of several compact binary systems and show how analysis of these observations reveals information about the structure, temperature, and opacity of the accretion region; the history of evolution and chemical processing in the binary; and the masses of the accretors, including black holes.

May 16 Charles Kerton (Iowa State)
New Views of teh Cygnus X Region

Cygnus X is the somewhat mysterious sounding name given to a region of intense star formation in our Galaxy. It is of interest to those studying star formation because it is the home of several OB associations, numerous HII regions and thousands of probable YSOs and embedded infrared sources. The standard interpretation of Cygnus X is that one is looking along the local spiral arm/spur of our Galaxy and seeing numerous star-forming regions piled-up along the line of sight. This talk will review some recent "new views" of Cygnus X in the radio and infrared. We will see how these observations are giving new life to an alternative idea that the majority of the star-formation activity seen in Cygnus X is associated with a giant molecular cloud (GMC) at 1.5 kpc thus providing us with the opportunity to examine the structure of a GMC in great detail.

Previous colloquia series: Fall 2002 Spring 2003 Fall 2003 Spring 2004 Fall 2004 Spring 2005 Fall 2005 Spring 2006 Fall 2006 Spring 2007 Fall 2007
Contact for program information: Daniel Dale (ddale @