Lithium in the Coma Berenices open cluster

Free access article

Issue		A&A Volume 369, Number 3, April III 2001


Page(s)		871 - 881
Section		Stellar clusters and associations
DOI		http://dx.doi.org/10.1051/0004-6361:20010235

A&A 369, 871-881 (2001)
DOI: 10.1051/0004-6361:20010235

Lithium in the Coma Berenices open cluster

A. Ford¹, R. D. Jeffries¹, D. J. James² and J. R. Barnes²

¹ Department of Physics, Keele University, Keele, Staffordshire ST5 5BG, UK
e-mail: rdj@astro.keele.ac.uk
² School of Physics and Astronomy, University of St. Andrews, North Haugh, St Andrews, Fife, KY16 9SS, UK
e-mail: djj@st-andrews.ac.uk

(Received 14 August 2000 / Accepted 12 February 2001 )

Abstract
Lithium abundances, radial velocities, and rotational velocities are reported for 20 candidate F, G and K stars of the sparse Coma Berenices open cluster. All the stars are proper-motion selected, and our radial velocities support the membership credentials of at least 12 of the candidates. Combining our data with that in the literature, we have 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. Several Coma Ber F stars have suffered significantly more Li depletion than their counterparts in the Hyades. The G and early-K stars of Coma Ber have undergone less Li depletion than those of the Hyades, but much more than that predicted by standard evolutionary models featuring only convective mixing. This provides strong evidence for additional mixing and Li depletion operating in these stars during their first 400 Myr on the main sequence, amounting to 0.3 dex at 6000 K and rising to 0.8-1.2 dex at 5400 K. We find that 4 of the radial-velocity non-members are among a small number of low-mass stars which were previously reported as part of an extra-tidal moving group associated with the Coma Ber cluster. As a result, we now find that the luminosity function of this moving group is indistinguishable from that of the central cluster. It is uncertain whether there may be a significant number of stars with even lower masses among the moving group.

Key words: stars: abundances -- stars: late type -- stars: interiors -- open clusters and associations: individual: Coma Berenices

Offprint request: A. Ford, af@astro.keele.ac.uk

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