CfA Colloquium Schedule Fall 2006
 7 September 2006

7 September 2006

Speaker: Joergen Christensen-Dalsgaard (University of Aarhus, Denmark)

Title:Helio- and asteroseismology: windows on stellar interiors
James Arthur Lecture

Abstract:Stellar surface layers are impenetrable to electromagnetic radiation. Hydrodynamic waves, however, travel with little attenuation through stellar interiors and their properties, as observed on stellar surfaces, therefore provide information about the internal properties of the star. This forms the basis for helio- and asteroseismology, analysing the surface manifestations of such waves. Over the past three decades helioseismology has yielded increasingly detailed information about the structure and dynamics of the solar interior and has allowed tests of subtle properties of the physics of the solar plasma. More recently, local helioseismology has allowed the study of subsurface structure of active regions as well as complex subsurface flows, sometimes characterized as Solar Subsurface Weather; remarkably, it has also been possible to investigate the properties of active regions on the far side of the Sun.
Asteroseismology, particularly of solar-like stars, has come under way more slowly, owing to the obvious difficulties of observing very small signals in distant stars. Studies of solar-like oscillations are now at a stage corresponding roughly to the state of helioseismology 25 years ago. However, the observational capabilities are developing rapidly, and we can expect extensive investigations of a broad range of stars over the next decade, providing a much more secure basis for our so far somewhat shaky understanding of the details of stellar evolution.

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