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Events on Tuesday, September 8th, 2009

Atomic Physics Seminar
Observation of ultra long-range Rydberg molecules
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Johannes Nipper, Universitaet Stuttgart, Germany
Abstract: At ultralow temperatures highly excited Rydberg atoms can form exotic molecules bound by a novel binding mechanism. First proposed by C. Greene and co-workers, these molecules are bound by low energy scattering of Rydberg electrons from polarizable ground state atoms. The resulting giant molecules can have an internuclear separation of several thousand Bohr radii, which places them among the largest known dimers to date.

Here we report on the experimental observation of the Rb(5S)-Rb(nS) dimer in a dense cloud of magnetically trapped Rubidium. The excitation spectra show the ground state and vibrationally excited states as well as trimer states, where two ground state atoms are bound to one Rydberg atom in a three body photoassociation process. The measured binding energies coincide with theoretical calculations taking into account s- and p-wave scattering. Lifetime measurements for the pure Rydberg state and the molecular dimer state show a decreased lifetime of the molecular state. Decay channels for the molecules are discussed. The coherent excitation dynamics of the dimer and the Rydberg state are studied in rotary echo experiments.
Host: Mark Saffman
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Chaos & Complex Systems Seminar
HIV/AIDS, What we know and how we learned it
Time: 12:05 pm
Place: 4274 Chamberlin (Refreshments will be served)
Speaker: Pete Cohen, UW Department of Medicine
Abstract: AIDS/HIV disease is arguably the most important disease in the world. I will attempt in 45 minutes to review how current understanding of how the disease evolved.
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Astronomy Colloquium
NCG 205 and M32, Understanding Andromeda's Tidally Distorted Satellites
Time: 3:30 pm
Place: 3425 Sterling Hall
Speaker: Kirsten Howley, Univeristy of California - Santa Cruz
Abstract: <br>
NGC 205 and M32 are close satellites of the Andromeda (M31) galaxy, and are our nearest examples of a dwarf elliptical (dE) and compact elliptical (cE) galaxy, respectively. Photometric observations strongly suggest NGC 205 and M32 are currently undergoing tidal distortion from their interaction with M31. In NGC 205, this conclusion is strengthened by the observation of an unusual velocity profile. Despite earlier attempts, the orbit and progenitor properties of NGC 205 are not well known. We perform an optimized search for these unknowns by combining a genetic algorithm with restricted N-body simulations of the interaction. Using NGC 205's photometric and kinematic observations as constraints, we carry out an effective exploration of the parameter space that defines the orbit and internal structure/dynamics of the progenitor satellite. We find that orbits best matching the observables place NGC 205 on primarily radial orbits moving from the Northwest to the Southeast with the satellite currently residing just behind M31. NGC 205's velocity appears near escape velocity, signifying it is likely on its first M31 passage. We also present Keck DEIMOS observations of M32's stellar kinematics well beyond the r &lt; 4 arc sec region probed in previous studies. The task is made challenging by the fact that M32 is projected against the bright/complicated inner regions of M31. Long-slit integrated light spectroscopy is used to measure the rotation curve of M32 out to a radius of about 1 arcmin. Beyond this radius, we present constraints based on multislit spectroscopy of resolved stars. The velocity distributions from the latter data set reveal a distinct M32 component. A by-product of our M32 study, is the characterization of the kinematics of the underlying M31 disk and inner spheroid.<br>
Host: Laura Chomiuk
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