Radial velocity distribution for the most probable single stars in the ONC (solid lines) and OB1b (dashed lines) samples. The thick solid and dashed lines refer to this work. The thin solid line represents the Gaussian fit to the Biazzo et al. (2009) sample obtained for 96 ONC targets with a mean V_rad = 24.87 km s^-1 ( km s^-1). The thin dashed line represents the histogram obtained by Briceño et al. (2007) for 30 OB1b stars with mean V_rad = 30.1 ± 1.9 km s^-1.