Snapshot of the radial velocity and the surface density transforming wave in the case of a B0-type star isothermal constant viscosity model (see Fig. 5), the time t_dyn ≈ 40 yr. The wave propagation velocity is denoted as D. In the model, the ratio Σ₁/ Σ₀ (surface densities behind and in front of the wavefront) is about one order of magnitude and slightly increases with the distance.