Lithium abundances in AGB stars and a new estimate for the⁷Be life-time

Abstract

Abstract. In most cases RGB and AGB stars with M≤ 2M destroy Li (which is instead synthesized trough electron-captures on 7 Be). This occurs through the combined operation of mixing processes and proton captures, when H-burning operates close to the envelope. Observed Li abundances are however difficult to explain, as they cover a wide spread. Various uncertainties affect model attempts, but so far the largest one concerns the processes of bound and free ecaptures on 7 Be, hence its life-time, whose known estimates are valid only for solar conditions. RGB and AGB stages have temperatures and densities below the envelope covering a wide range and differing from solar by up to a factor of five for T and up to five orders of magnitudes for ρ, hence extrapolations are unreliable. Recently, we presented an estimate of the 7 Be half-life based on a fully quantistic method that goes beyond the Debye-Hückel approximation. Here we discuss its consequences on Li nucleosynthesis in low mass AGB stars.

Theoretical Estimate of the Half-life for the Radioactive 134Cs and 135Cs in Astrophysical Scenarios

“…Furthermore, despite these transitions being quark-level processes, they also strongly depend on extra-nuclear factors, such as temperature and electron density, which significantly vary in the layers of evolved stars outside the degenerate core. Indeed, these parameters may affect the ionization degree of the atomic systems where the decay occurs, which in turn modifies the discrete-to-continuum transition ratio (Simonucci et al 2013;Palmerini et al 2016;Vescovi et al 2019).…”