Relative variation of Lyα and metal line spectra for various values of α_V and α_D. The x-axis shows the frequency in velocity units where the zero point is set at the resonance of the line (for doublets, the line with the shortest wavelength is used) and denoted by a dotted grey line. Note that the normalised intensity in the main panels is in log scale to highlight both emission and absorption features. In each panel, the inset zooms on the absorption region on the blue side of the resonance (y-axis now in linear scale). The values for the fixed wind parameters are V_max = 400 km s⁻¹, b = 20 km s⁻¹, and τ_d = 0. For Lyα, the H I column density is N_HI = 10¹⁸ cm⁻². The Mg⁺, Fe⁺, Si⁺ column densities are fixed to N = 10¹⁴ cm⁻² whereas we take N = 10¹⁵ cm⁻² for C⁺, owing to the fact that carbon is roughly ten times more abundant than the other elements according to solar values.