sigma Ori GTC+INT spectroscopy

We complemented the information with Gaia DR2 astrometric data and other features of youth (mid-infrared excess, X-ray emission) compiled with Virtual Observatory tools and from the literature. Of the 168 observed targets, we determined for the first time spectral types of 39 stars and equivalent widths of LiI and H{alpha} of 34 and 12 stars, respectively. We identified 11 close ({rho}<~3-arcsec) binaries resolved by Gaia, of which three are new, 14 strong accretors, of which four are new and another four have H{alpha} emission shifted by over 120km/s, two juvenile star candidates in the sparse population of the Ori OB1b association, and one spectroscopic binary candidate.

Remarkably, we found 51 cluster non-members, 35 of which were previously considered as sigma Orionis members and taken into account in high-impact works on, e.g., disc frequency and initial mass function.