I_E vs. I_E – J_E colour–magnitude diagram for the σ Orionis part of the FoV. The black points are all the Euclid sources that remain after applying all the cuts. Benchmark objects are denoted with red circles. New objects near the cluster sequence are denoted with blue squares and labelled with capital letters. Known sources other than the benchmarks in the σ Orionis cluster are denoted with green circles. An ATMO CEQ isochrone (see Phillips et al. 2020) for an age of 3 Myr and a distance of 402.74 pc is shown. Theoretical masses are labelled on the isochrone.