Response of the line Hu₁₄ to the mass-loss rate. Top panel: As the mass-loss increases, the line changes from an absorption profile to a single-peaked emission. The mass-loss interval goes from 1.5 × 10⁻⁷ M_⊙ yr⁻¹ to 4 × 10⁻⁷ M_⊙ yr⁻¹, in a step of 0.5 × 10⁻⁷ M_⊙ yr⁻¹. The maximum intensity of the single-peaked emission is achieved when Ṁ = 3.5 × 10⁻⁷ M_⊙ yr⁻¹ (solid blue line), and then the intensity decreases (solid green line). Bottom panel: Synthetic double-peaked-profiles were obtained from 4.5 × 10⁻⁷ M_⊙ yr⁻¹ to 7 × 10⁻⁷ M_⊙ yr⁻¹. The behaviour is non-monotonic. Then, as the mass loss increases, the profile turns to a P Cygni one (for Ṁ > 7.5 × 10⁻⁷ M_⊙ yr⁻¹).