Upper left panel: comparison between the separated IUE spectra (black) of the primary and secondary stars around the He ii λ 1640 line and the corresponding synthetic spectra (red). The primary spectrum is shifted upwards by 0.5 for clarity. The other three panels display a comparison between the SWP03008 (upper right), SWP54350 (lower left) and SWP02755 (lower right) IUE spectra taken at phases 0.0, 0.25 and 0.75 in black and the synthetic binary spectra obtained through combination of CMFGEN primary and secondary spectra at given phases in red.