Fig. 4. The spectral difference between ¹²CO₂ and ¹³CO₂. Top : pure ¹²CO₂  T=800 K, N=10 cm^-2; Bottom : pure ¹³CO₂  T=800 K, N=10 cm^-2; middle : the observed continuum subtracted spectrum of EP Aqr. All spectra are normalized to the maximum intensity and are hence only illustrative for the different band positions, not the band intensities. The insets show blow-ups of the 15.4 and 16.2 regions.