Hot bottom burning and s-process nucleosynthesis in massive AGB stars at the beginning of the thermally-pulsing phase

García-Hernández, D. A.; Zamora, O.; Yagüe, A.; Uttenthaler, S.; Karakas, A. I.; Lugaro, M.; Ventura, P.; Lambert, D. L.
Bibliographical reference

Astronomy and Astrophysics, Volume 555, id.L3, 6 pp.

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7
2013
Number of authors
8
IAC number of authors
3
Citations
68
Refereed citations
50
Description
We report the first spectroscopic identification of massive Galactic asymptotic giant branch (AGB) stars at the beginning of the thermal pulse (TP) phase. These stars are the most Li-rich massive AGBs found to date, super Li-rich AGBs with log ɛ (Li) ~ 3-4. The high Li overabundances are accompanied by weak or no s-process element (i.e. Rb and Zr) enhancements. A comparison of our observations with the most recent hot bottom burning (HBB) and s-process nucleosynthesis models confirms that HBB is strongly activated during the first TPs but the 22Ne neutron source needs many more TP and third dredge-up episodes to produce enough Rb at the stellar surface. We also show that the short-lived element Tc, usually used as an indicator of AGB genuineness, is not detected in massive AGBs, which is in agreement with the theoretical predictions when the 22Ne neutron source dominates the s-process nucleosynthesis. Appendix A is available in electronic form at http://www.aanda.org
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Nucleosynthesis and molecular processes in the late stages of Stellar Evolution
Low- to intermediate-mass (M < 8 solar masses, Ms) stars represent the majority of stars in the Cosmos. They finish their lives on the Asymptotic Giant Branch (AGB) - just before they form planetary nebulae (PNe) - where they experience complex nucleosynthetic and molecular processes. AGB stars are important contributors to the enrichment of the
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García Hernández