Observed (histogram) and modelled profiles (lines) of the H30α. The red dashed line is the best profile obtained by using the Walmsley departure coefficients (with the input parameter values as given in Martín-Pintado et al. 2011), while the solid red line is the modelled profile obtained with the set of input parameters shown in Table 1 and by using the Storey & Hummer b_n coefficients. The derived amplification assuming the Walmsley coefficients is lower because of their lower negative β_mn values (see Fig. 2). The arrow indicates the wing hump at the blue-shifted velocities.