Measured EW(Hα) of our sample of stars as a function of adopted spectral type. The black dashed line shows the curve fitting from K0 to L0 of the EWs used in Barrado y Navascués & Martín (2003) as an empirical criterion for identifying classical T Tauri stars. The black dotted line shows the coarse extrapolation of the Barrado y Navascués & Martín (2003) criterion to spectral types earlier than K0 (EW(Hα) = –3.9 Å). Big and small red filled circles indicate cluster member stars and brown dwarfs with EWs above and below the black lines, respectively. Big and small blue crosses show non-cluster-member stars with EWs above and below the black lines, respectively. The early K-type σ Orionis star with strong emission is Mayrit 871071 (Haro 5-27, V510 Ori), the driving source of the jet HH 444 (Reipurth et al. 1998; López-Martín et al. 2001).