Chemical abundances of late-type pre-main sequence stars in the σ Orionis cluster

¹ Observatoire de Paris-Meudon, GEPI, 5 place Jules Janssen, 92195 Meudon Cedex, France e-mail: Jonay.Gonzalez-Hernandez@obspm.fr
² Cosmological Impact of the First STars (CIFIST) Marie Curie Excellence Team, France
³ Dpto. de Astrofísica y Ciencias de la Atmósfera, Facultad de Física, Universidad Complutense de Madrid, 28040 Madrid, Spain
⁴ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁵ Consejo Superior de Investigaciones Científicas, Spain
⁶ Laboratorio de Astrofísica Espacial y Física Fundamental, INTA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain 


Received: 16 June 2008
Accepted: 23 August 2008

Abstract

Context. The young σ Orionis cluster is an important location for studying the formation and evolution of stars, brown dwarfs, and planetary-mass objects. Its metallicity, although it is a fundamental parameter, has not been well determined yet.

Aims. We present the first determination of the metallicity of nine young late-type stars in σ Orionis.

Methods. Using the optical and near-infrared broadband photometry available in the literature we derive the effective temperatures for these nine cluster stars, which lie in the interval 4300–6500 K (1–3 ). These parameters are employed to compute a grid of synthetic spectra based on the code MOOG and Kurucz model atmospheres. We employ a -minimization procedure to derive the stellar surface gravity and atmospheric abundances of Al, Ca, Si, Fe, Ni and Li, using multi-object optical spectroscopy taken with WYFFOS+AF2 at the William Herschel Telescope ().

Results. The average metallicity of the σ Orionis cluster is (random and systematic errors). The abundances of the other elements, except lithium, seem to be consistent with solar values. Lithium abundances are in agreement with the “cosmic” ⁷Li abundance, except for two stars which show a in the range 3.6–3.7 (although almost consistent within the error bars). There are also other two stars with . We derived an average radial velocity of the σ Orionis cluster of  .

Conclusions. The σ Orionis metallicity is roughly solar.