Convective proton and He-3 ingestion into helium burning: Nucleosynthesis during a post-AGB thermal pulse

A thermal pulse during the post-AGE phase of stellar evolution may lead to a unique mode of light element nucleosynthesis. The stage is set by the ing estion of the unprocessed envelope material into the hot He-flash convectio n zone below. If the temperature is sufficiently large and the C-12 abundan ce high enough (e.g. T-8 > 0.8, X(C-12), similar or equal to 0.4 and X(H) s imilar or equal to 1 . 10(-3)) protons react faster with C-12 and form C-13 than destroying Be-7. The latter forms by alpha -capture of He-3 after an initial reduction of the He-3 abundance to about 3 . 10(-5)X(He-4) by the p pI reaction He-3(He-3,2p)He-4 (for T-8 similar or equal to 1). All He-3 is burned within minutes to weeks depending on the temperature. 7Be is now pre sent at about the previously mentioned level of 3He. Its further fate is de termined by the reactions Be-7(e(-),v)Li-7 and the alpha -capture reactions of Be-7 and Li-7. These captures lead to the production of B-11 which in t urn is finally destroyed by B-11(alpha, n)N-14. The details of this mechani sm of light element production in real stars is expected to be fairly depen dent on the description of mixing.