Simulated stellar wind of GJ 504. The star is at the centre and its rotation axis lies along the positive z_★. The x_★−y_★ plane is coloured by the total wind velocity. The Alfvén surface is the region of space where the local wind speed matches the Alfvén wave speed, ${\mathrm{v}}_{\mathrm{A}}{\mathrm{B}}_{\mathrm{w}}/\sqrt{4\pi {\rho }_{\mathrm{w}}}$ (in cgs units), and is depicted as a translucent surface with two lobes, as expected for stars with dominant dipolar large-scale field configurations. The colour bar indicates the total wind velocity (u_tot).