Velocity profile as a function of radius for a set of 20 M_⊙ stellar models with different mass-loss rates (as in Fig. 1). The black continuous lines indicate models with Ṁ ≥ 5 × 10⁻⁶ M_⊙ yr⁻¹ (5, 10, 20, 30, 50 × 10⁻⁶), while the orange dot-dashed lines indicate models with Ṁ = 8 × 10⁻⁶ M_⊙ yr⁻¹ computed with plane parallel grey atmosphere. The green dashed line indicates the local isothermal sound speed.