Different analysis steps of the simulated observations. Panel a: raw synthetic observation (number of photons as a function of wavelength and phase). Panel b: data after the telluric correction, as described in the text. Panel c: data of panel b after subtracting the total wavelength and phase mean, and normalising each column byits standard deviation, to suppress noisy wavelength regions. This is data set A. Panel d: same as panel c, but with the signal of all contaminant line absorbers removed, making the lines originating from ¹³C¹⁶O visible. Thisis data set B.