The Creation of Lithium in Giant Stars

Extract

A time-dependent “convective diffusion” algorithm for convective transport in the mixing-length framework has been coupled for the first time with a self-consistent full evolutionary computation, in order to investigate theoretically the creation of superrich lithium stars on the asymptotic giant branch. For intermediate mass stars in the mass range from 4 to 7 M_⊙ with both Population I and II compositions, hot bottom burning in the convective envelope was found, with maximum temperatures T_ce at the base of the convective envelope ranging from 20 to 100 million K, depending on stellar mass and mass loss rates. For T_ce ≥ 40 million K, lithium-rich giants were produced (with log ε(⁷Li) ≳ 1, i.e., above the normal observed range in giants). For T_ce ≥ 50 million K, superrich lithium giants were created, with log ε(⁷Li) ≳ 3 (i.e., larger than the present cosmic⁷Li abundance).