Predicted behavior of the evolutionary tracks computed by Ekström et al. (2012, left panels) and Brott et al. (2011, right panels) in the Oeq-log (L/L_⊙) diagram. From top to bottom, the sections of the evolutionary tracks, which are located within the three regions (“a”, “b”, and “c”, respectively) indicated in Fig. 8 and described in Sect. 3.5, are highlighted with blue and green thicker lines. In addition, the gray thick part of the evolutionary tracks indicates that the corresponding section of the track lies inside the region of the sHRD close to the ZAMS where no O stars are detected. The stars in the observed sample that populate the three considered regions of the sHRD are also included in each panel, separately, for comparison (this time using v sin i values instead of v_eq). As in other figures, we indicate three v sin i values of interest (50, 150, and 300 km s⁻¹) with vertical lines. Size represents log q value.