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Observing convection in stellar atmospheres

Published online by Cambridge University Press:  01 August 2006

John D. Landstreet
John D. Landstreet*
Affiliation:
Department of Physics & Astronomy, UWO, London, ON N6G 1P7, Canada email: jlandstr@astro.uwo.ca
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Abstract

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Convection occurs in the visible photospheric layers of most stars having Te less than about 10000 K, and in some hotter stars. The solar granulation pattern is a symptom of this, as is the non-zero microturbulent velocity often required in abundance analysis to make both weak and strong lines yield the same abundance.

In very sharp-lined stars, the presence of a non-thermal velocity field in the visible stellar atmosphere leads to several other effects which may be detected in spectral line profiles. These include radial velocities that vary systematically with equivalent width, distortions of the line profile as compared to a profile computed with a Voigt profile and rotational broadening (“macroturbulence”), and asymmetries with respect to the line centre (“bisector curvature”).

Detection and interpretation of these effects, with the goal of obtaining empirical information about a velocity field present in the visible layers, requires comparison with calculated synthetic spectra which incorporate model velocity fields. Thus, this review will summarize some of the observational clues concerning photospheric velocity fields, as well as modelling aimed at interpreting these data.

Keywords

ConvectionSun: atmospherestars: atmospheresline: profilesline: formation
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 2 , Symposium S239: Convection in Astrophysics , August 2006 , pp. 103 - 112
Copyright
Copyright © International Astronomical Union 2007

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