IS THERE A CLASSICAL HYADES LITHIUM PROBLEM

The distribution of surface lithium abundances in the Hyades cluster, as a function of effective temperature, has resisted a satisfactory theoretical explanation for more than two decades. Trends in the historically recomputed values of stellar opacity have stimulated us to investigate systematically the effects that larger opacities would have on lithium depletion during the pre-main-sequence evolution of low-mass stars. We show that the calculated depletion depends quite strongly on the opacities employed, and that both surface and interior opacities play an important role. By performing standard evolutionary calculations with parameterized increments in the opacities, we are able to produce the observed Hyades (Li, Teff) relation for G and K dwarfs (i.e., for Teff ≤ 6300 K) in a manner consistent with the other observational constraints. The solution presented herein requires an increase in interior opacities at ∼4 × 106 K over older values by ≤37%. Such a change is not incompatible with the historical trends in opacity computations and suggests that the resolution of this problem lies solely in the opacities, without recourse to other physical mechanisms such as turbulent diffusion or "extra mixing.".