The solar Lithium problem: is the explanation due solely to mixing or also to the e−-capture decay rate of ⁷Be?

¹ Department of Physics and Geology, University of Perugia, Via A. Pascoli, 06123, Perugia, Italy
² I.N.F.N., Section of Perugia, Via A. Pascoli, 06123 Perugia, Italy

^* e-mail: diegontt92@gmail.com

Published online: 30 December 2017

Abstract

The nucleosynthesis of ⁷Li is one of the most crucial problems in nuclear as- trophysics, as its observations in several sites are hard to be explained. Concerning the Sun, the most common interpretations of the low Li abundance invoke either burning in early stages or non-convective mixing below the envelope. Here we apply a diffusive mechanism of mixing, together with a recent estimate of the rate for e−-captures on ⁷Be, to establish whether the solar Li destruction should be attributed to purely pre-Main Se- quence (MS) nuclear processes or if the coupling of mixing and nucleosynthesis on the MS can account for it. Our preliminary results indicate that, whether Li survives the pre- MS phase, the changes of the ⁷Be e⁻-capture rate do not affect its production/destruction. The low Li abundance should then depend only on diffusion processes from the bottom of the convective envelope to the lowerlying tachocline zone. We suggest that, if diffusive processes occurred over the age of the Sun, they required diffusive mass transfers of a few 10⁻¹³ M_⊙/yr to explain the Li drop. This is a high estimate: future works will tell us if it is realistic or not. In this second case, pre-MS burning would remain the only alternative.