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Diffusion, Meridional Circulation and Mass Loss in Main Sequence and Horizontal Branch Stars

Published online by Cambridge University Press:  19 July 2016

G. Michaud
G. Michaud*
Affiliation:
Département de Physique Université de Montréal C.P. 6128, succursale A Montréal Qué., H3C 3J7 Canada

Abstract

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Photospheric abundances are used to determine the importance of atomic diffusion, meridional circulation, mass loss and turbulence in main sequence and horizontal branch stars. Atomic diffusion leads to the appearance of the Li gap and the AmFm and HgMn phenomena at approximately the Teff at which they are observed. It leads to a 12 to 25% reduction in the age of halo stars. The Li abundance in Halo stars is probably 50% of the original abundance. Atomic diffusion competes with meridional circulation. The V sin i at which the HgMn and AmFm phenomena disappear give an argument in favour of the meridional circulation model of Tassoul and Tassoul. Mass loss is probably present in AmFm stars and cooler F stars but only at the rate of 10-15 M⊙ yr-1. In many objects, the turbulent particle diffusion coefficient is at most 10 times larger than the atomic diffusion coefficient.

Type
The Lower Main Sequence
Information
Symposium - International Astronomical Union , Volume 145: Evolution of Stars: The Photospheric Abundance Connection , 1991 , pp. 111 - 124
Copyright
Copyright © Kluwer 1991 

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