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.
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