Hot Bottom Burning And S-Process Nucleosynthesis In Massive Agb Stars At The Beginning Of The Thermally-Pulsing Phase

Garcia-Hernandez, D. A.
Zamora, O.
Yague, A.
Uttenthaler, S.
Karakas, A. I.
Lugaro, M.
Ventura, P.
Lambert, D. L.
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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 epsilon (Li) similar to 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 Ne-22 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 Ne-22 neutron source dominates the s-process nucleosynthesis.

García-Hernández, D. A., Olga Zamora, A. Yagüe, Stefan Uttenthaler, A. I. Karakas, Maria Lugaro, Paolo Ventura, and D. L. Lambert. >Hot bottom burning and s-process nucleosynthesis in massive AGB stars at the beginning of the thermally-pulsing phase.> Astronomy & Astrophysics, Vol, 555 (Jul., 2013): L3.