Chemical composition of the young open clusters IC 2602 and IC 2391 ^*,**

¹ Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 2, Firenze, Italy e-mail: vdorazi@arcetri.astro.it
² INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, Firenze, Italy

Received: 23 December 2008
Accepted: 21 April 2009

Abstract

Context. Galactic open clusters have been long recognized as one of the best tools to investigate the chemical content of Galactic disk and its time evolution. In the last decade, many efforts have been directed to chemically characterize the old and intermediate age population; surprisingly, the chemical content of the younger and close counterpart remains largely undetermined.

Aims. In this paper we present the abundance analysis of a sample of 15 G/K members of the young pre-main sequence clusters IC 2602 and IC 2391. Along with IC 4665, these are the first pre-main sequence clusters for which a detailed abundance determination has been carried out so far.

Methods. We analyzed high-resolution, high spectra acquired with different instruments (UVES and CASPEC at ESO, and the echelle spectrograph at CTIO), using MOOG and equivalent width measurements. Along with metallicity ([Fe/H]), we measured Na i, Si i, Ca i, Ti i and Ti ii, and Ni i abundances. Stars cooler than ~5500 show lower Ca i, Ti i, and Na i than warmer stars. By determining Ti ii abundances, we show that, at least for Ti, this effect is due to NLTE and over-ionization.

Results. We find average metallicities [Fe/H] = 0 ± 0.01 and [Fe/H] = -0.01 ± 0.02 for IC 2602 and IC 2391, respectively. All the [X/Fe] ratios show a solar composition; the accurate measurements allow us to exclude the presence of star-to-star scatter among the members.