log (g) − log (T_eff) diagram (left) and evolution of the abundance ratio N/H (right) for the 7 (blue), 15 (red), and 32 M_⊙ (green) rotating models. The track of the non-rotating 15 M_⊙ is indicated with the red dotted line. Observational points from O- and B-type stars are plotted, with empty symbols for luminosity class (LC) V-III (triangles: Morel et al. 2008; squares: Villamariz et al. 2002, Villamariz & Herrero 2005; circles: Przybilla et al. 2010) and filled symbols for LC I (triangles: Takeda & Takada-Hidai 2000; squares: Crowther et al. 2006; hexagons: Searle et al. 2008; circles: Przybilla et al. 2010).