Comparison between the synthetic spectrum of the M = 60M_⊙ star classified as O9.5Ib (red dot-dashed line) and the observed spectrum of HD 167263 a O9.5III giant (left panel), HD 36486 a O9.5II bright giant (middle panel), and HD 188209 a O9.5Iab supergiant (right panel). The synthetic spectrum has been convolved with Vsini-v_mac equal to 80–100 km s^-1 (left), 130−160 km s^-1 (middle) and 55−70 km s^-1 (right).