[Triumf-seminars] TRIUMF Colloquium today at 14:00

[postmaster at admin.triumf.ca]

Date/Time: Wed 2009-03-11 at 14:00

Location:  Auditorium          

Speaker:   Lars Freyhammer (University of Central Lancashire)

Title:     Laboratories of Atomic Diffusion theory: The Atmospheres of roAp Stars

Abstract: Atomic diffusion is an important process in several types of stars, including the Sun, and is highly pronounced in the class of rapidly oscillating Ap stars (roAp). These have atmospheres that are characterized by abundance stratification caused by atomic diffusion in the presence of strong global magnetic fields (sometimes seen as Zeeman-split absorption lines). Their spectra show abnormal Sr-Cr-Eu abundances, typically with strong lines of rare-earth elements. The global, rapid oscillations have short wavelengths compared to the atmospheric depth, and stratified elements such as Fe, Eu, Nd and Pr probe different parts of the pulsation geometry. Furthermore, seismic techniques (asteroseismology) may be applied to determine the star's radius and study its atmospheric structure. The pulsation axis is aligned with that of the magnetic field, but is different from the rotation axis, which during a full rotation cycle provides a unique opportunity for studying the full pulsation geometry and atmospheric element distribution in 3D. I will describe the roAp class characteristics, illustrated with high resolution spectroscopic observations from the European Southern Observatory. Instrumentation and data analysis with model spectra will briefly be described. Special emphasis will be on a recent study where two Chile-Hawaii 8-m telescopes were combined to construct 2D maps of the surface element distribution of a roAp star.

Stimulants available 15 minutes before the talk.

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