Disentangled single-star spectra shifted to the presumed rest frame. The disentangled spectrum of the narrow-lined stripped star (dark blue) and the fast-rotating Be companion star (orange) are shown in selected wavelength ranges. Both component spectra have been rescaled assuming light ratios of 0.6 and 0.4 for the narrow-lined star and the broad-lined star, respectively (see Sect. 6.1.2). The rapid rotation of the Be companion is apparent, for example, in the He I line at 4471.5 Å (centre panel at bottom). The narrow lines in the spectrum of the Be star, including the one at 4300 Å, are spurious and arise from disentangling artefacts and telluric or interstellar absorption.