Elemental abundances of low-mass stars in the young clusters 25 Orionis and λ Orionis

Aims. We aim to derive the chemical pattern of the young clusters 25 Orionis and lambda Orionis through homogeneous and accurate measurements of elemental abundances. Methods. We present FLAMES/UVEs observations of a sample of 14 K-type targets in the 25 Ori and lambda Ori clusters. We measured their radial velocities to confirm cluster membership. We derived stellar parameters and abundances of Fe, Na, Al, Si, Ca, Ti, and Ni using the code MOOG. Results. All 25 Ori stars are confirmed cluster members without evidence of binarity; in lambda Ori we identify one non member and one possible single- lined binary star. We find an average metallicity [Fe/H] = - 0.05 +/- 0.05 for 25 Ori, where the error is the 1s standard deviation from the average. The lambda Ori members have a mean Fe abundance value of 0.01 +/- 0.01. The other elements show close- tosolar ratios and no star- to- star dispersion. Conclusions. Our results, along with previous metallicity determinations in the Orion complex, show a small but detectable dispersion in the [Fe/H] distribution of the complex. This appears to be compatible with large- scale star formation episodes and initial nonuniformity in the precloud medium. We show that, as expected, the abundance distribution of star- forming regions is consistent with the chemical pattern of the Galactic thin disk.