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Astrophysics Colloquium


Fall 2008 - Coordinated by R.D. Gehrz
Held in Physics 210 at 3:00pm on Fridays
(unless otherwise noted)


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September 5 No Colloquium - First Week of Classes
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September 12 -
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September 19 Dr. Bob Lysak, UMN
Title: The Alfvenic Aurorae
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Host: T.J. Jones
September 26 Dr. Alex Heger, UMN
Title: Burning Neutron Stars
Abstract: The probably by far most common thermonuclear explosion to occur in nature is the explosion of a thin layer of material, about the height of the physics building, that has accumulated on the surface of a neutron star, about the size of Minneapolis, in a binary star system - Type I X-ray bursts. I show theoretical models for such outbursts, their very specific mode of nuclear burning unheard of in any other stellar system, as well as their much bigger cousins, the superbursts. I will discuss our current difficulty in understanding how those are made, and possible solutions.
Host: T.J. Jones
October 3 No Colloquium - Dept. Picnic
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October 10 Dr. Josh Semeter, BU
Title: Structure and Motion in the Aurora
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Host: B. Lysak
October 17 Colloquium to be hosted by Aerospace Engineering, 2:30 - 3:30, Rapson Hall 31
Prof. N. Jeremy Kasdin, Princeton University
Title: Are We Alone? Imaging Extrasolar Earthlike Planets from Space
Abstract: Nothing has captured the human imagination more than the prospect of life outside our own solar system. We are incredibly fortunate that our generation may for the first time get a peak at other worlds, an opportunity to search for life outside our own neighborhood. NASA is currently engaged in a series of mission studies, one of which is being led from Princeton, for a large space observatory to image extrasolar earthlike planets. Such an observatory could be launched as early as the next decade; it will search for terrestrial planets in the habitable zone of roughly 150 nearby stars and characterize them for the potential to harbor life. It will culminate 20 years of indirect planet finding with the first direct image of an extrasolar Earthlike planet. This talk will discuss the recent history of planet finding methods and two concepts being studied at Princeton for a planet finding space telescope, an internal coronagraph and an external occulter. An internal coronagraph uses specially designed masks in the optical train of the telescope, combined with deformable mirrors and a wavefront control system, to attenuate the light from the star and make the companion planet visible. An external occulter is a large screen (roughly 50 m in diameter) flying far from the telescope (about 72,000 km). The occulter blocks the starlight from entering the telescope while letting the planet light through. I'll describe the technologies behind these two methods and our progress in both mission design and laboratory verification.
Host: Aerospace Engineering
October 24 Dr. Justin Revenaugh, UMN Geology
Title: The Bowels of the Earth
Abstract: Earth's mantle is 2/3's of the planet by mass and nearly 90% by volume. Throughout Earth's geological history, it has played a major, but often overlooked, role. The rise of atmospheric oxygen, supercontinent breakup, mass extinction events, water in the oceans... if it was a major event in geology, you can be sure the mantle had a part to play. In this talk, I will familiarize the audience with the mantle as it stands today and talk about it's evolution through time as seen in geology, geochemistry and geophysics.
Host: T.J. Jones
October 31 Dr. Jürgen Ott, Caltech
Title: Ammonia in the Local (and not so Local) Universe
Abstract: Dense molecular gas is considered to be the fuel for star formation in galaxies. To understand the formation of molecular gas, the gravitational collapse of the dense gas into stars and the energetic impact of young massive stars on the ambient clouds in detail, it is therefore indispensable to accurately measure its physical properties such as density and temperature. The transitions of ammonia, the most abundant top-heavy molecule, can be utilized as an easy-to-use thermometer for this important gas phase. Over the last few years, a new generation of 1cm receivers at ATNF and other telescopes has been commissioned which enables astronomers to exploit this peculiar feature of ammonia in far more objects than before. In this talk, I will present results from extensive ammonia observations toward the Galactic Center, nearby starburst and ultraluminous-infrared galaxies, the Magellanic Clouds, and gravitational lenses.
Host: S. Warren
November 7 Dr. R.D. Gehrz, UMN
Title: The Stratospheric Observatory for Infrared Astronomy (SOFIA)
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Host: R.D. Gehrz
November 14 Dr. Brian R. McNamara, U of Waterloo
Title: A New Spin on AGN Feedback in Clusters and Galaxies
Abstract: The hot, gaseous atmospheres of galaxies and clusters of galaxies are repositories for the energy output from active galactic nuclei (AGN) over cosmic time. X-ray observations are showing that star formation fueled by gas condensing out of hot atmospheres is strongly suppressed by AGN feedback. Dubbed "radio mode" feedback, this mechanism may solve several outstanding problems in astrophysics, including the numbers of luminous galaxies and their colors, and the excess number of hot baryons in the Universe. I present new evidence that the most energetic AGN outbursts may be powered by rapidly-spinning, ultra-massive black holes.
Host: P. Mendygral
November 21 Dr. Nathan Smith, UC Berkeley
Title: Mass Loss and Pre-SN evolution of Massive Stars
Abstract: I will discuss the role that mass loss plays in the pre-supernova evolution of massive stars in a variety of different scenarios, and what observable effect it may have on the resulting SN explosion. The amount of mass lost, its speed, and how soon before core collapse the material is lost can have a dramatic effect on the resulting SN lightcurve and spectrum. Massive stars trek across the HR diagram as they evolve, and the resulting SN can look very different depending on where along this path core collapse occurs. It may not depend solely on initial mass, because many of the potential progenitors of Types Ib, Ic, IIn, IIb, and II-L overlap in their range of likely initial mass. It will therefore be very difficult to use SNe as probes of stellar evolution until this connection is understood. The most extreme pre-SN mass ejections in massive luminous blue variables (LBVs) have recently (and surprisingly) been linked to the very luminous Type IIn supernovae with extremely strong circumstellar interaction that dominates the spectrum and enhances the visual luminosity. In some cases these objects require strong LBV-like shell ejections in the *decades* immediatley before a SN. This may suggest that some massive stars become surprisingly unstable in the very final stages of nuclear burning before core collapse, for reasons that are not yet fully understood.
Host: R.D. Gehrz
December 5 Dr. Brian Hart, U California, Irvine
Title: Galaxy Clusters: Giants of the Universe
Host: R.D. Gehrz
December 12 No Colloquium - Last week of classes
Abstract: I present the recent discoveries of two Galactic massive young clusters, which together contain 40 Red Supergiants - 20% of all those known in the Galaxy, and as many in the entire Large Magellanic Cloud. From observations and evolutionary synthesis models, we argue that the cluster masses are comparable to the other Galactic 'Super Star Clusters' such as Westerlund 1 and the Arches Cluster. The two clusters are located at the base of the Scutum-Crux spiral arm, and appear to lie at the tip of the Galactic Bar. Therefore, these objects can be used as a probe to study the star-formation history and evolution of the Galaxy. Further, the distinctly different ages of the clusters, uniform metallicity, and large number of RSGs, mean that these objects now offer an unprecedented opportunity to study the pre-supernova evolution of massive stars.
Host: R.M. Humphreys
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May 9 -
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