Illustration of the impact of a binary companion on the velocity field. Given the simulations shown in Fig. 9 (El Mellah et al. 2020), the dotted black line represents the 1D isotropic radial velocity profile (w.r.t. the star). The dotted blue line is the radial velocity profile in the direction of the secondary, and the dotted red line is the radial velocity profile in the direction opposite to the secondary. For comparison, the dashed black curve illustrates the β-velocity law (Eq. (4)) for β​ = ​5 representing the single-star situation. For better comparison with the observed velocity profiles (Sect. 5.2), the same figure but with a linear x-axis is shown in Fig. A.1. See text for more details.