Green curve: the O₂ transmittance computed by TAPAS and convoluted for the appropriate resolution of 44 000, in a narrow spectral interval where O₂ lines are present (right scale). Black curve (left scale): the star spectrum showing absorption lines due to telluric O₂, shifted from the TAPAS transmission, because the FEROS wavelength calibration put the star spectrum in the barycentric solar system reference. Dark purple curve: star spectrum divided by the convoluted transmittance, after proper wavelength shift (left scale, but vertically displaced for clarity). A conspicuous line remaining corresponds to an O₂ line absent from the HITRAN 2008 database. Other small wiggles correspond to weak H₂O lines, as indicated by the light blue curve (H₂O only TAPAS transmittance, left scale).