Predicted intensities for the lines involved in the spectral type criterion for late O stars in the LMC as a function of T_eff for ɛ_Si = 7.0 dex and three values of log g. The grey rectangle indicates the temperature range of our sample. The vertical arrows indicate the temperature at which the Si III λ4553/He II λ4542 ratio equals unity,which defines the O9.7 subtype at solar metallicity: t1 = 32.5 kK, log g = 4.2; t2 = 31.85 kK, log g = 4.0, and t3 = 30.9 kK, log g = 3.8. The values of v sin i, R, and v_mic are the same as in Fig. 6.