Variation of the observed excess feature as a function of the average hardness ratio (H − S)/(H + S) (see Sect. 2.5). Panels a–d: variations of the central wavelength of the G1 component described in Sect. 2.5, the total G1 + G2 normalization assuming unabsorbed Gaussian components, the total equivalent width, and total normalization assuming absorption. The vertical lines in (a), (b), and (d) show the fits with a constant model.