Talks & Events
Special Seminars: 2012
Stellar Turbulence, and why we should care
David Arnett, Steward Observatory, University of Arizona
Supercomputers allow the simulation of three-dimensional highly turbulent flow. Treating these numerical "experiments" as valid representations of the behavior of high energy density (HED) plasma, a view supported by laboratory experiments with inertial confinement fusion (ICF) devices, we are beginning to develop a theory of this behavior appropriate to stellar interiors. Unlike conventional astrophysical convection theory, the Richardson-Kolmogorov turbulent cascade and the Lorenz strange attractor make an appearance, as well as a rich set of boundary-region physics. The process of developing physical insight from numerical simulations will be illustrated, and implications for stellar evolution, from the Sun to gamma-ray bursts and supernovae, will be discussed.
Molecular Data for Interstellar Studies: CO, CH, and C2
Ultraviolet data acquired with the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer have wide spectral bandpasses and high signal-to-noise ratios, thereby providing the means to detect relatively weak features from atoms and molecules. Here I focus on our analyses of transitions in CO, CH, and C2 associated with diffuse molecular clouds. The comparisons with well-characterized absorption bands allows us to derive oscillator strengths (or equivalently absorption cross sections), which have led to an improved understanding of the molecule's structure. The high-quality astronomical spectra also yield predissociation rates that provide further insight into the structure. Where possible, comparison with experimental and theoretical results will be highlighted.
Probing Stellar Nucleosynthesis through Interstellar Isotope Ratios
High-resolution spectra of diffuse molecular clouds allow us to study isotope ratios for lithium and rubidium. These ratios provide information on the contributions from massive stars to Li and Rb production in the current epoch, which will be the focus of my talk. Cosmic-ray spallation, where relativistic protons break apart interstellar CNO nuclei, is a key process for the synthesis of light elements, including Li. For neutron-capture elements such as Rb, the weak s-process, where neutron capture is slower than beta decay, and the r-process are important. The weak s-process occurs in the He- and C-burning shells of the stars, while the r-process is thought to arise during the core-collapse supernova at the end of the star's life. Cosmic rays are accelerated to relativistic energy in the supernova event.