Fitted iSHELL line profiles for the CO υ = 1−0, υ = 2−1, υ = 3−2, and the CO υ = 1−0 transitions. The median line profile is shown in black, whereas the fitted line profile is shown in green. For the ¹²CO transitions, we have indicated the narrow and broad components in, respectively, blue and red. The faint, grey line profiles visible in the background correspond to the individual line profiles used in creating the weighted−averaged, normalised line profile.