Fraction of initial spin–orbit orientations that end up aligned by a given age and with a given orbital period due to orbital evolution, assuming the frequency-dependent ﹩{Q}_{\star }^{{\prime} }﹩ given by Equation (2). The host star is 1 M_⊙ in all cases. The spin-down parameters are taken from (Irwin et al. 2007), and the three panels are for planet masses of 0.5, 1 and 3 M_Jup.