O₂ forbidden – transition band B (1–0) at 6880 Å. The same background correction as in Fig. 10 has been applied (see text). Upper plot: the solid line represents the altitude information extracted from the SOPHIE data, while the dotted line is the model calculation, in which O₂ absorption is included from 6856 Å upwards. The narrow atmospheric signatures due to the O₂ absorption are clearly seen. The sharp peaks perfectly match the model with respect to spectral positions, while their heights could be quite different. Lower plot: the thick solid line again represents the evaluated altitude for the 0.0003 zero level correction, while the thin dash-dotted lines show the extreme possible variations of the estimated levels due to the 0.0002 (lower evaluations in the peaks and higher ones in the continuum) and 0.0004 (higher evaluations in the peaks and lower ones in the continuum) zero level corrections.