Lithium in the Coma Berenices open cluster

Lithium abundances, radial velocities, and rotational velocities are report ed for 20 candidate F, G and E;stars of the sparse Coma Berenices opt rt cl uster. All the stars are proper-motion selected, and our radial velocities support the membership credentials of at least 12 of the candidates. Combin ing our data with that in the literature, we haw a close-to-complete census of Li abundances for late-type stars with M-V < 5.8. These data show that the Li-depletion pattern in Coma Ber is similar, but not identical, to that in the Hyades cluster, which has a similar age but higher metallicity. Sev eral Coma Ber F stars have suffered significantly more Li depletion than th eir counterparts in the Hyades. The G and early-it stars of Coma Ber have u ndergone less Li depletion than those of the Hyades, Gut much more than tha t predicted by standard evolutionary models featuring only convective mixin g, This provides strong evidence for additional mixing and Li depletion ope rating in these stars during their first 400 Myr on the main sequence, amou nting to 0.3 dex at 6000 Ii and rising to 0.8-1.2 dex at 5400 Ii. We find t hat ii of the radial-velocity non-members are among a small number of low-m ass stars which were previously reported as part of an extra-tidal moving g roup associated with the Coma Eel cluster. As a result, we now find that th e luminosity function of this moving group is indistinguishable from that o f the central cluster. It is uncertain whether there may be a significant n umber of stars with even lower masses among the moving group.