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Lithium production by thermohaline mixing in low-mass, low-metallicity asymptotic giant branch stars

Published online by Cambridge University Press:  23 April 2010

Richard J. Stancliffe ,
George C. Angelou  and
John C. Lattanzio
Richard J. Stancliffe
Affiliation:
Centre for Stellar and Planetary Astrophysics, Monash University, VIC 3800, Australia email: [email protected]
George C. Angelou
Affiliation:
Centre for Stellar and Planetary Astrophysics, Monash University, VIC 3800, Australia email: [email protected]
John C. Lattanzio
Affiliation:
Centre for Stellar and Planetary Astrophysics, Monash University, VIC 3800, Australia email: [email protected]
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Abstract

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We examine the effects of thermohaline mixing on the composition of the envelopes of low-metallicity asymptotic giant branch (AGB) stars. We have evolved models of 1, 1.5 and 2M⊙ and of metallicity Z = 10−4 from the pre-main sequence to the end of the thermal pulsing asymptotic giant branch with thermohaline mixing applied throughout the simulations. We find that the small amount of 3He that remains after the first giant branch is enough to drive thermohaline mixing on the AGB and that the mixing is most efficient in the early thermal pulses, with the efficiency dropping from pulse to pulse. We note a surprising increase in the 7Li abundance, with log10ϵ(7Li) reaching values of over 2.5 in the 1.5M⊙ model. It is thus possible to get stars which are both C- and Li-rich at the same time. We compare our models to measurements of carbon and lithium in carbon-enhanced metal-poor stars which have not yet reached the giant branch. These models can simultaneously reproduced the observed C and Li abundances of carbon-enhanced metal-poor turn-off stars that are Li-rich.

Keywords

Stars: evolutionAGB and post-AGBPopulation IIcarbon
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 5 , Symposium S268: Light Elements in the Universe , November 2009 , pp. 405 - 410
Copyright
Copyright © International Astronomical Union 2010

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