The chemical composition of the Orion star forming region

Context. Recent accurate abundance analyses of B-type main sequence stars in the solar vicinity has shown that abundances derived from these stellar objects are more homogeneous and metal-rich than previously thought. Aims. We investigate whether the inhomogeneity of abundances previously found in B-type stars in the Ori OB1 association is real (hence a signature of enrichment of the newly formed stars in an induced star formation scenario) or a consequence of intrinsic errors induced by the use of photometric indices to establish the stellar parameters prior to the abundance analysis. Methods. We obtained a new (improved) spectroscopic data set comprising 13 B-type stars in the various Ori OB1 associations, and performed a detailed, self-consistent spectroscopic abundance analysis by means of the modern stellar atmosphere code fastwin