Photospheric micro-turbulence of the sample non-pulsating stars separated by SpT and LC (open circles – LC III/I; solid circles – LC V/IV) as a function of log g (left) and T_eff (right). In the top panels over-plotted are: the v_mic velocities of a sample of O stars in the SMC derived by means of the CMFGEN code (from Heap et al. 2006), and the theoretical T_eff and log g scales of O stars in the MW predicted by Martins et al. (2005a) (red solid (DWs) and dashed (SGs) vertical lines). In each plot, the representative error bars are also indicated. For more information, see Sect. 4.