True value of the ratio as a function of r/R_⋆ for a typical O type star (relevant parameters are color-coded and listed above and in the body of each panel). This ratio controls the wind emission due to recombination of ionized hydrogen, i.e., the higher its value, the greater the emission. We used Eq. (2) with the different values of V_cl (color-coded in the body of each figure) to calculate f_cl.