Metallicity of low-mass stars in Orion

Context. Determining the metal content of low-mass members of young associations provides a tool that addresses different issues, such as triggered star formation or the link between the metal-rich nature of planet-host stars and the early phases of planet formation. The Orion complex is a well known example of possible triggered star formation and is known to host a rich variety of proto-planetary disks around its low-mass stars. Available metallicity measurements yield discrepant results. Aims. We analyzed FLAMES/UVES and Giraffe spectra of low-mass members of three groups/clusters belonging to the Orion association. Our goal is the homogeneous determination of the metallicity of the sample stars, which allows us to look for [Fe/H] differences between the three regions and for the possible presence of metal-rich stars. Methods. Nine members of the ONC and one star each in the lambda Ori cluster and OB1b subgroup were analyzed. After the veiling determination, we retrieved the metallicity by means of equivalent widths and/or spectral synthesis using MOOG. Results. We obtain an average metallicity for the ONC [Fe/H] = -0.01 +/- 0.04. No metal-rich stars were detected and the dispersion within our sample is consistent with measurement uncertainties. The metallicity of the lambda Ori member is also solar, while the OB1b star has an [Fe/H] significantly below the ONC average. If confirmed by additional [Fe/H] determinations in the OB1b subgroup, this result would support the triggered star formation and the self-enrichment scenario for the Orion complex.