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Extra-Mixing in Luminous Cool Red Giants: Hints from Evolved Stars With and Without Li

Published online by Cambridge University Press:  05 March 2013

R. Guandalini ,
S. Palmerini ,
M. Busso  and
S. Uttenthaler
R. Guandalini*
Affiliation:
Dipartimento di Fisica, Università degli Studi di Perugia, via Pascoli, 06123 Perugia, Italy INFN Sezione di Perugia, via Pascoli, 06123 Perugia, Italy
S. Palmerini
Affiliation:
Dipartimento di Fisica, Università degli Studi di Perugia, via Pascoli, 06123 Perugia, Italy INFN Sezione di Perugia, via Pascoli, 06123 Perugia, Italy
M. Busso
Affiliation:
Dipartimento di Fisica, Università degli Studi di Perugia, via Pascoli, 06123 Perugia, Italy INFN Sezione di Perugia, via Pascoli, 06123 Perugia, Italy
S. Uttenthaler
Affiliation:
Instituut voor Sterrenkunde, K. U. Leuven, Celestijnenlaan 200D, 3000 Leuven, Belgium
*
DCorresponding author. Email: guandalini@fisica.unipg.it
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Abstract

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We present an analysis of Li abundances in low mass stars (LMS) during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stages, based on a new determination of their luminosities and evolutionary status. By applying recently suggested models for extra-mixing, induced by magnetic buoyancy, we show that both Li-rich and Li-poor stars can be accounted for. The simplest scenario implies the development of fast instabilities on the RGB, where Li is produced. When the fields increase in strength, buoyancy slows down and Li is destroyed. 3He is consumed, at variable rates. The process continues on the AGB, where however moderate mass circulation rates have little effect on Li due to the short time available. O-rich and C-rich stars show different histories of Li production/destruction, possibly indicative of different masses. More complex transport schemes are allowed by magnetic buoyancy, with larger effects on Li, but most normal LMS seem to show only the range of Li variation discussed here.

Keywords

nuclear reactions, nucleosynthesis, abundancesstars: AGBstars: evolutionstars: red giants
Type
Theory, Evolution and Models
Information
Publications of the Astronomical Society of Australia , Volume 26 , Issue 3 , 2009 , pp. 168 - 175
Copyright
Copyright © Astronomical Society of Australia 2009

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