ESPaDOnS spectrum of BD+40 4220 (red line) in the region of the three 4634 and 4640 Å N III and 4686 Å He II stellar wind emission lines. Superimposed is an average of the two spectra that have been previously observed by Rauw et al. (1999) for orbital phases 0.178 and 0.193 of the binary system. A Doppler shift of +216 km s⁻¹ has to be applied to match the ESPaDOnS data, a value in agreement with the average orbital phase of 0.185. The same Doppler shift will be applied to the two 9402.5 and 9424.5 Å N III stellar wind emission lines simulated in Fig. 6.