Position of the primary (open square) and secondary (filled square) stars in the Hertzsprung-Russell diagram (upper panels) and the log g–log T_eff diagram (lower panels) along with evolutionary tracks for single massive stars at solar metallicity during the core-hydrogen burning phase (Ekström et al. 2012). In the left panels, the evolutionary tracks correspond to non-rotating stars, whilst the right panels yield the results for stars rotating at 0.4 ×. The dotted red lines correspond to isochrones of 3.2 and 6.3 million years for the left panels and of 4.0 and 8.0 million years for the right panels.