Normalised spectrum of five relevant spectroscopic epochs. They are offset vertically by 0.25 (0.3 in the right panel) for visualisation purposes; the colours correspond to their X-ray state, as defined in Fig. 1. The identified transitions in this wavelength range are marked with dotted lines: black for H, red for He I, blue for He II, and green for other metallic lines (Bowen blend at ∼ 4640 Å). Telluric bands and interstellar features are shown as grey and yellow shadowed regions, respectively. The E20 spectrum was smoothed through convolution with a Gaussian for visualisation purposes.