Extracted CO spectra. The panels show extracted CO spectra (blue histograms) and the best-fit model presented in Sect. 6. The model was shifted using a systemic velocity of 7.4 km s⁻¹. From left to right, we present spectra extracted from apertures with diameters of 45, 90, 135, 180, and 240 mas. From top to bottom, the lines shown are CO v = 1,  J = 3 − 2, CO v = 0,  J = 2 − 1, CO v = 1,  J = 2 − 1, and ¹³CO v = 0,  J = 3 − 2.