The Rotational History of Solar-Type Stars: Does It Affect Lithium Abundances?

Abstract

Recent studies of lithium abundances in solar-type stars suggest that second order effects, such as rotation and/or mass-loss, might affect the rate at which lithium is depleted at the surface of cool stars. This conclusion mainly stems from the dispersion of lithium abundances observed in late-type stars with otherwise similar mass and age. The dispersion of lithium abundances is relatively small in pre-main sequence (PMS) stars [1], reaches a maximum of about 2 dex in ZAMS stars (Soderblom, this volume), and decreases later during main sequence evolution, although significant dispersion may still be present by the age of the Sun [2], and perhaps even during the giant stage (Balachandran, this volume).Such a pattern of lithium dispersion is difficult to understand in the framework of conventional models in which lithium burning occurs at the base of the convective zone of non-rotating, non-mass losing stars. That two stars of the same age and mass can exhibit different lithium content strongly suggests that other, so far neglected, mechanisms play a role in lithium depletion.In this context, it may be relevant to stress that the pattern of lithium dispersion varies with age in much a similar way than does the dispersion of stellar rotation, namely: the dispersion in both rotation rates and lithium abundances is relatively small in the PMS stage, then strongly increases from the PMS to the ZAMS, and subsequently decreases on the main sequence. The parallel evolution of the range of lithium abundances and of rotation rates observed in solar-type stars is strongly suggestive of a physical link between rotation and lithium depletion.