Mixing on the main sequence: Lithium and beryllium in old open clusters

Abstract

Lithium surveys of very young clusters indicate that solar-type stars undergo very little (if any) Li depletion during the pre-main sequence phases (e.g., [8]); on the other hand, according to standard models of stellar evolution (those including convection only), solar-type stars should not destroy Li while on the main sequence (MS), since the base of their convective zones does not extend deep enough to reach the layers where Li has been burnt. Yet, the Sun has a very low Li abundance, a factor of ∼ 100 lower than the meteoritic value, which is representative of the original solar Li content. This evidence of MS Li depletion has motivated theoreticians to introduce non-standard processes in the models (see [4], [15] and references therein); at the same time, a large amount of observational effort has been devoted to Li (and, to some extent, to Be) surveys with the goal of placing empirical constraints on proposed mechanisms. In this paper I will review the current empirical scenario, focusing on the results from old open clusters (ages ≥ 600 Myr). © 2006 Springer-Verlag Berlin Heidelberg.