EDP Sciences
Free Access
Volume 372, Number 3, June IV 2001
Page(s) 862 - 878
Section Galactic structure, stellar clusters and populations
DOI https://doi.org/10.1051/0004-6361:20010339
Published online 15 June 2001

A&A 372, 862-878 (2001)
DOI: 10.1051/0004-6361:20010339

Membership, lithium, and metallicity in the young open clusters IC 2602 and IC 2391 : Enlarging the sample

S. Randich1, R. Pallavicini2, G. Meola2, J. R. Stauffer3 and S. C. Balachandran4

1  Osservatorio Astrofisico di Arcetri, Largo Fermi 5, 50125 Firenze, Italy
    e-mail: randich@arcetri.astro.it
2  Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
3  Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
4  Department of Astronomy, University of Maryland, College Park, MD 20740, USA

(Received 24 January 2000 / Accepted 2 March 2001)

We present lithium abundances for ~50 X-ray selected candidate members of the 30-50 Myr old open clusters IC 2602 and IC 2391. These data enlarge and extend to cooler temperatures previous Li surveys of these clusters by Stauffer et al. (1989) and Randich et al. (1997). We also give for the first time an estimate of the metallicity of the two clusters which turns out to be close to solar. Radial velocity measurements together with H$\alpha$ chromospheric emission and the presence/absence of other spectroscopic features are used to ascertain the membership status for the sample stars not yet confirmed as cluster members; rotational velocities have also been determined for all sample stars. Stars more massive than ~1 $M_{\odot}$ in both clusters show no sign of significant Li depletion, while lower mass stars are all lithium depleted, with the amount of Li depletion increasing to cooler temperatures. We confirm that the late-G and early-K stars in IC 2602 present a star-to-star scatter in Li abundances similar to, but not as large as the one in the Pleiades . A scatter is also seen among late-K and M dwarfs. Unlike in the Pleiades and clusters, the scatter among early-K stars in IC 2602 shows only marginal correlation with rotation. Our data suggest that the drop-off of lithium towards lower masses may start at an earlier color in IC 2391 than in IC 2602, but larger cluster samples are needed to confirm this result. In addition, whereas G and early K stars in the two clusters are, on average, more Li rich than their counterparts in the Pleiades, a fraction of the coolest stars, in particular in IC 2391, are as depleted as the lowest-Li Pleiades stars of the same mass. If they continue depleting Li on their way to the main sequence, they are expected to be more Li depleted than the Pleiades at the age of the latter cluster.

Key words: open clusters and associations: individual: IC 2602 -- open clusters and associations: individual: IC 2391 -- stars: abundances -- stars: interiors

Offprint request: S. Randich, randich@arcetri.astro.it

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