CfA Colloquium Schedule Spring 2006
 9 March 2006

9 March 2006

Speaker: Steve Cranmer (CfA)

Title:Leaky Stars: Pulsations, Waves, and Turbulence in Stellar Winds across the H-R Diagram

Abstract:All stars are believed to possess expanding outer atmospheres known as stellar winds. Continual mass loss has a significant impact on stellar evolution, on the chemical evolution of galaxies (including the mass and energy budgets of the interstellar medium), and even on the long-term evolution of planetary atmospheres. Most stars are also observed to pulsate in a variety of modes. Although much of the pulsational energy remains trapped inside stars, some of it can escape as outward propagating waves and turbulence. This talk will highlight recent advances in our understanding of the interactions between these fluctuations and the mean plasma state of an extended stellar atmosphere (e.g., the mass loss rate, density, temperature, and outflow speed). Cool, solar-type stars have chromospheres and coronae that are believed to be heated, at least in part, by waves. For example, the importance of magnetohydrodynamic (MHD) turbulence in the solar wind has been affirmed by the surprising measurements of the UVCS instrument on SOHO that heavy ions are heated to hundreds of times the temperatures of protons and electrons, indicating Alfven wave dissipation. In contrast, the hottest and most luminous stars (O, B, and Wolf-Rayet) do not have coronae, but they exhibit radiatively driven winds that are accelerated by efficient momentum transfer between the intense radiation field and the plasma. Despite the differences in origin, there exist similar connections between stellar pulsations, circumstellar variability, and a wave-modified mean plasma state in both hot and cool stars.

Video of the Presentation (Talks can be viewed with RealPlayer. Free download is available from )


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