出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：A recent survey of a large sample of massive Galactic asymptotic giant branch (AGB) stars shows
that significant overabundances of rubidium (up to 100 times solar) are present in these stars. Zirconium,
on the other hand, is not enriched compared to the solar abundance. These observations
can set constraints on our theoretical notion of the slow neutron capture process (the s process)
in AGB stars, as well as on the rates of the neutron capture reactions involved in the production
of Rb and Zr. Li abundances are also reported for these stars. Li is made via proton captures at
the base of the convective envelope (hot bottom burning; HBB) in AGB models of mass higher
than ≈ 5 M⊙. We present predictions of Rb, Zr, and Li abundances for AGB stars of masses 5,
6, and 6.5 M⊙. We find increasing Rb overabundances with increasing stellar mass, as observed,
but we are far from matching the highest observed Rb enhancements, unless the third dredge up
efficiency remains as high as before the onset of the superwind phase during the final few pulses
of a massive AGB star. We predict large variations in the Li abundances, which are observed.
Finally, we show that the Rb production increases with a decrease in the stellar metallicity, at a
given mass. This result may be useful to constrain the source of abundance anomalies observed
in Globular Cluster Stars.
