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

摘要

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 ingestion of the unprocessed envelope material into the hot He-flash convection zone below. If the temperature is sufficiently large and the C-12 abundance high enough (e.g. T-8 > 0.8, X(C-12), similar or equal to 0.4 and X(H) similar 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 ppI 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 present at about the previously mentioned level of 3He. Its further fate is determined 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 turn is finally destroyed by B-11(alpha, n)N-14. The details of this mechanism of light element production in real stars is expected to be fairly dependent on the description of mixing. [References: 12]