Mean spectra in the O VI doublet region for the 2001 (dashed line) and 2003 (solid line) epochs. Fluxes are in ergs cm⁻² s⁻¹ Å⁻¹. The zero point has been adjusted for the 2001 spectrum by subtracting ﹩1.3\times 10^{-14}﹩ in order to match the continuum levels. The overall 2003 profile is higher in the central region, while the airglow and absorption features match well. H₂ absorbers can be identified from the model spectrum plotted in the bottom panel. The strongest airglow lines (including Lyβ at 1026 Å) have been edited out manually, but their positions are marked. Note the change in the position of the absorption feature near 1020–1021 Å.