Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...308..773d&link_type=abstract
Astronomy and Astrophysics, v.308, p.773-784
Astronomy and Astrophysics
Astrophysics
90
Stars: Abundances, Stars: Evolution, Diffusion, Stars: Interiors, Globular Clusters: General
Scientific paper
Additional mixing between the hydrogen burning shell and the base of the convective envelope in stars on their first ascent of the red giant branch is traditionally considered as a possible cause for the star-to-star abundance variations in globular clusters. In the present paper we model this deep mixing by diffusion. Nuclear kinetics equations coupled with diffusion terms are solved to follow the evolution of stellar surface abundances for isotopes taking part in reactions of the pp-chains, CNO-, NeNa- and MgAl-cycles. Our task is to reproduce the "global anticorrelation" of [O/Fe] versus [Na/Fe] found recently in globular cluster and halo giants by Kraft et al. (1993) and the correlation of [C/Fe] with M_V_ observed in M92 (Langer et al. 1986). It is shown that both correlations can be accounted for by deep diffusive mixing with parameters for mixing depth and rate adjusted individually for each correlation. The deep mixing in red giants with solar metallicity is demonstrated to allow the interpretation of anomalous ^17^O/^16^O and ^18^O/^16^O isotope ratios in S and C asymptotic giant branch stars. In the conclusion we propose an observational test for the discussed deep mixing.
Denissenkov Pavel A.
Weiss Alexander
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