Properties of the supposed youngest stars in the sample. Left: sHRD highlighting a subsample of 118 LS O-type stars with log g > 3.7 dex. The symbol size depends on the value of the ratio v sin i/v_crit, as indicated. Right: υ sin i/v_crit distributions (as normalized histograms) for the indicated subsample, separating those stars located above (upper panel) and below (lower panel) the 32 M_⊙ track. The vertical dashed lines mark several values of interest for the v sin i/v_crit ratio (see text for explanation). The vertical dotted line at v sin i/v_crit = 0.06 marks the approximate limit below which the v sin i determination can be affected by methodological limitations in those stars located above the 32 M₀ track).