Best-fit LTE model for the HCN 2ν₂ overtone band and the interloping H₂O lines at 7 μm for f_bg = 1. The pink shaded area indicates the spectral region used in the fit. A simultaneously fit H₂O model is also shown. The HCN overtone lines are labelled, and the residuals are shown in the bottom panel. A fiducial model of the HCN 3ν₂−ν₂ band, with N(HCN) = 2 × 10¹⁸ cm⁻², T_vib = 330 K, T_rot = 50 K, and f_bg = 1 is shown in purple. The grey shaded area in the bottom panel indicates the 68% interval of the residuals.