Top panel: sky distribution of the sources belonging to group B_5, b (brown empty squares), group B₅ (brown dots), and all the sources in the Belt region defined in the text (grey dots). The orange stars mark the position of σ Ori, ζ Ori, ϵ Ori, η Ori, and δ Ori. Bottom panels: distribution in 3D galactic co-ordinates of group B_5, b (brown squares), and of all the sources belonging to the Belt region (grey dots).