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Stellar Surface Convection, Line Asymmetries, and Wavelength Shifts

Published online by Cambridge University Press:  12 April 2016

Dainis Dravins
Dainis Dravins*
Affiliation:
Lund Observatory, Box 43, SE-22100 Lund, Sweden

Abstract

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Wavelength positions of photospheric absorption lines may be affected by surface convection (stellar granulation). Asymmetries and wavelength shifts originate from correlated velocity and brightness patterns: rising (blueshifted) elements are hot (bright), and convective blueshifts result from a larger contribution of such blueshifted photons than of redshifted ones from the sinking and cooler (darker) gas. For the Sun, the effect is around 300 m s−1, expected to increase in F-type stars, and in giants. Magnetic fields affect convection and induce lineshift variations over stellar activity cycles. A sufficient measuring precision reveals also the temporal variability of line wavelengths (due to the evolution of granules on the stellar surface). A major future development to come from adaptive optics and optical interferometry will be the study of wavelength variations across spatially resolved stars, together with their spatially resolved time variability. Thus, precise radial velocities should soon open up new vistas in stellar atmospheric physics.

Type
Part 7. Convection, Line Asymmetry
Information
International Astronomical Union Colloquium , Volume 170: Precise Stellar Radial Velocities , 1999 , pp. 268 - 277
Copyright
Copyright © Astronomical Society of the Pacific 1999

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