Optical spectrum of CI Cam. Panel a: 4000–9000 Å spectrum of CI Cam, convolved with a Gaussian function to approximately match the resolution of those presented in Fig. 1 of Hynes et al. (2002) to allow for easy comparison. Panel b: original, un-binned line profiles of the stronger hydrogen and helium lines in velocity space, corrected for the systemic velocity of CI Cam, −51 ± 2 km s⁻¹ (Aret et al. 2016). Panel c: systemic redshift corrected 4545–4560 Å region, convolved with a boxcar function with width 13 pixels, corresponding 0.2 Å. Panel d: region around the He II 4686Å line, also redshift corrected and convolved with a boxcar function of width 13 pixels. Panel e: region around the Na D interstellar absorption components, convolved with a boxcar function and with no redshift correction applied.