Iron-abundance distribution of members of the Orion complex (ONC, OB1b, OB1a, σ Ori, 25 Ori, and λ Ori) taken from the most recent literature (González-Hernández et al. 2008; Biazzo et al. 2011) and this work. Symbols with different sizes denote three different metallicity bins: [Fe/H]  ≤  −0.10, −0.09  ≤  [Fe/H]  ≤  0.00, and [Fe/H]  >  0.00, from the smallest to the largest sizes. The central bin corresponds to the average metallicity of the Orion complex  ± 1σ. The mean metallicity of each subgroup is written in parenthesis. The circle outlines the Briceño et al. (2005) boundary of the Orion OB subgroups.