Chemical pattern across the young associations ONC and OB1b

The authors present a comprehensive differential abundance analysis, relative to the Sun, for alpha (Na, Al, Si) and Fe-peak (Ca, Ti, Fe, Ni) elements in a sample of low-mass stars (with Teff from 4000 to 6000 K) in the Orion Nebula Cluster (ONC) Ori OB1b using high-resolution FLAMES spectra. One ONC star, P1455, is marginally metal rich, but the mean [X/H] values for all elements in both groups are statisticlly consistent with solar metallicity. The two groups show homogeneous abundances, hence effective mixing in the formation stage, and no statistically significant difference in the mean abundances on the length scale of the separation, tens of parsecs. There is no evidence of self-enrichment, particularly for Ti and Si that could be supernova nucleosytnhetic products. The paper is a benchmark result for theories of triggered and sequential star formation and the search for young extrasolar planetary systems.