Comparison of different derived wind velocity profiles from the literature (Table 7). See text for more details of the models. These are mostly the solutions for the wind without accounting for the ionization of the neutron star, except in the case of two of the models by Sander et al. (2018) and, at the bottom, the velocity profile calculated by Watanabe et al. (2006) along the line connecting donor and neutron star. The range of possible distances covered by the neutron star on its eccentric orbit (Bildsten et al. 1997) and the orbital velocity range, mainly driven by the uncertainty in inclination, are indicated as well. In the upper left corner we indicate approximately how wind (shown as horizontal lines) and orbital velocity (vertical) would combine at the mean neutron star distance from HD 77581 for three of the reported velocity profiles. These differences have a strong effect on the expected accretion flow close to the neutron star (see Sect. 4.1).