Projected rotational velocity vs. amplitude of the radial velocity variations in the primary stars sample (114 stars). The shaded regions show approximately where we expect tidal synchronization to play a role during the main sequence evolution for a primary mass of 20 and 60 M_⊙ (with R = 8 and 10 R_⊙, respectively). Here we varied the mass ratios q from 0.25 and 1 and periods P_orb from 0.25 to 10 days. The labels on the top and right hand axes show the corresponding orbital and spin period for a typical circular binary system assuming a 20 M_⊙  primary and a mass ratio of 0.5.