Membership, rotation, and lithium abundances in the open clusters NGC 2451 A and B

Abstract

High-resolution spectra of 30 late-type and 9 early-type candidate members of the young (∼50-80 Myr) open clusters NGC 2451 A and B have been analyzed in order to complement our previous photometric and X-ray study. Cluster membership of these X-ray selected stars has been confirmed or rejected on the basis of radial velocity and Hα chromospheric emission. The metallicity of both clusters seems to be about solar - contrary to previous investigations. Lithium abundances have been determined by two different methods, namely curve-of-growth techniques and spectrum synthesis, yielding quite consistent results. The pattern of Li abundances versus effective temperature resembles that of the equally-old Alpha Per cluster, i.e., little Li depletion is seen for solar-type and earlier-type stars, while towards cooler stars Li is more and more depleted, possibly showing a star-to-star scatter below ∼5200 K. The hottest star in our sample shows a Li abundance ∼0.5 dex higher than the meteoritic value. Rotational velocities have been determined in order to investigate the supposed dependence of activity and Li depletion on rotation.