Sample objects located in the spectroscopic HRD, spectroscopic luminosity versus log-scale effective temperature, with 1σ error bars. Stellar evolution tracks (Ekström et al. 2012, for v_rot = 0.4v_crit and Z = 0.014) ranging in ZAMS-masses from 9 to 32 M_⊙ are indicated in alternating colours of blue and black. The dashed lines depict the corresponding tracks for non-rotating models. Numbers denote the internal sample star IDs.