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

¹ Institut für Theoretische Physik und Astrophysik, Universität Kiel, Olshausenstraße 40, 24118 Kiel, Germany
² INAF–Osservatorio Astrofisico di Arcetri, Largo Fermi 5, 50125 Firenze, Italy
³ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany

Corresponding author: M. Hünsch, mhuensch@astrophysik.uni-kiel.de

Received: 19 June 2003
Accepted: 15 January 2004

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 ~ 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.