The Mixing of Lithium

Abstract

The observational status of the problem of lithium abundances has been thoroughly detailed in the preceding papers in this symposium, and it is clear why we must consider how matter is mixed from outer convection zones to inner, hotter regions. The need for appropriate mixing mechanisms has also been nicely brought out by Herbig and Wolff, and Böhm has summarized the role of convective mixing. Conventional mixing-length models for the outer convection zones seem to give qualitatively reasonable results for the depletion during pre-main-sequence contraction but do not completely account for the observations, and it seems inescapable that main-sequence depletion of lithium must be considered. I shall therefore simplify the discussion of mixing by concentrating on main-sequence models in the following outline of some possible mixing processes, though most of the remarks to be made should apply generally to other phases. I shall also pretend that there is one principle mechanism (or combination of them) that must be found, though stars in different evolutionary phases, or with different masses, may deplete lithium quite differently. Further, I shall use the Sun as an illustration in general since we know some important details about it that are not always known for other stars.