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Mixing and the s-Process in Rotating AGB Stars

Published online by Cambridge University Press:  26 May 2016

Falk Herwig ,
Norbert Langer  and
Maria Lugaro
Falk Herwig
Affiliation:
Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Rd, Victoria, BC, V8P 1A1, Canada
Norbert Langer
Affiliation:
Astronomical Institute, Universiteit Utrecht, P.O. Box 80000, NL-3508 TA Utrecht, The Netherlands
Maria Lugaro
Affiliation:
Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, United Kingdom

Abstract

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We model the nucleosynthesis during a radiative interpulse phase of a rotating 3 M⊙ Asymptotic Giant Branch (AGB) star. We find an enhanced production of the neutron source species 13C compared to non-rotating models due to shear mixing of protons and 12C at the core-envelope interface. We estimate that the resulting total production of heavy elements by slow neutron capture (s-process) is too low to account for most observations. This due to the fact that rotationally induced mixing during the interpulse phase causes a pollution of the 13C pocket layer with the neutron poison 14N. As a result we find a maximum neutron exposure of τmax = 0.04 mbarn–1 in the s-process layer of our solar metallicity model with rotation. This is about a factor of 5 … 10 less than required to reproduce the observed stellar s-process abundance patterns. We compare our results with models that include hydrodynamic overshooting mixing, and with simple parametric models including the combined effects of overshooting and mixing in the interpulse. Within the parametric model a range of mixing efficiencies during the interpulse phase correlates with a spread in the s-process-efficiency. Such a spread is observed in AGB and post-AGB stars as well as in pre-solar SiC grains.

Type
Session 4 Rotation and Stellar Evolution
Information
Symposium - International Astronomical Union , Volume 215: Stellar Rotation , 2004 , pp. 467 - 472
Copyright
Copyright © Astronomical Society of the Pacific 2004 

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