Clumping influence on the spectral lines. The figures show the influence a change in f_cl has on the line profile of on one hand the H α recombination line and on the other hand the Si IV 1400 resonance doublet. Both model spectra are using almost the same input, they only differ in mass-loss rate and clumping. The blue line both has Ṁ = 8 · 10⁻⁸ M_⊙/yr, and is highly clumped (f_cl = 40). The orange line is a smooth outflow but has a significantly higher mass-loss rate (Ṁ = 5 · 10⁻⁷ M_⊙/yr); the product $\sqrt{f_{\mathrm{cl}}}\dot{M}$ is thus the same for both lines. If we assume an optically thin clumping over the complete line forming region, the 2 H α lines would show perfect agreement. However, this is not the case as we use models that relax the optically thin assumption and are only clumped above a fitted onset-velocity.