Probability density of the inclination of the stellar spin-axis of τ Boo A i_A (derived from v sin i, R_* and P_rot, see Table 1), the orbital inclination angle of τ Boo Ab i_Ab (determined via the planetary radial velocity signal by Brogi et al. 2012) and the orbital inclination angle of τ Boo B i_AB (determined from our MCMC analysis). The similarity of the three inclination angles suggests a coplanar, aligned system.