THE AGE-MASS RELATION FOR CHROMOSPHERICALLY ACTIVE BINARIES .2. LITHIUM DEPLETION IN DWARF COMPONENTS

We present an extensive study of lithium abundances in dwarf component s of chromospherically active binary stars (CABS). Since most of these binaries have known radii, masses and ages, this kind of data is espe cially useful for comparisons with theoretical models which try to exp lain the Li depletion phenomenon. We show that a significant part of t hese stars have clear Li overabundances with respect to the typical va lues for stars of the same mass and evolutionary stage. These excesses are evident when comparing our sample of CABS with binary and single stars belonging to open clusters of different ages, namely Pleiades, H yades, NGC752, M67 and NGC188, which have ages ranging from 7x10(7) to 10(10) yr. The Li excesses are more conspicuous for masses in the ran ge 0.75-0.95 M., indicating that the rate of Li depletion has been les s pronounced in CABS than in single stars. This phenomenon is interpre ted in the context of transport of angular momentum from the orbit to the stellar rotation due to tidal effects. This angular momentum trans fer would avoid the radial differential rotation and the associated tu rbulent mixing of material in the stellar interior. Other explanations , however, can not be ruled out. This is the case of transport of mate rial induced by internal gravity waves, which could be inhibited due t o the presence of strong magnetic fields associated with the effective dynamo in CABS. The confirmed existence of a relation between Li abun dances and the fluxes in Ca II H&K lines can also be accommodated with in both scenarios.