log  g_c vs. log  T_eff (upper panel) and spectroscopic Hertzsprung-Russell (lower panel) diagrams of the O-type giants, bright giants, and supergiants, where (see Sect. 4.2). Symbols and colors have the same meaning as in Fig. 5. Evolutionary tracks and isochrones are for models that have an initial rotational velocity of approximately 200 kms^-1 (Brott et al. 2011; Köhler et al. 2015). In the lower panel, the right-hand axis gives the classical Eddington factor Γ_e for the opacity of free electrons in a fully ionized plasma with solar helium abundance (cf. Langer & Kudritzki 2014). The horizontal line at log  L/ L_⊙ = 4.6 indicates the location of the corresponding Eddington limit. The dashed straight lines are lines of constant log  g as indicated. Lower opacities of the green and blue symbols and the numbers in parentheses in the legend have the same meaning as in Fig. 1.