Measured altitude, velocity, and brightness temperature of the CO layers as a function of radius: ¹²CO (blue), ¹³CO (red), and C¹⁸O (green). Data points were extracted for all channel maps and binned according to distance. The error bars represent the dispersion within the bins added quadratically to the uncertainty resulting from inclination (48 ± 3°). Left: solid lines display a broken power-law fit (below and above r = 300 au) for the ¹²CO and ¹³CO. Centre: black solid line represents the Keplerian velocity for a 1 M_⊙ central star, derived from the C¹⁸O position-velocity diagram (Appendix A). The shaded area represents an uncertainty of 0.1 M_⊙. The red and blue dashed lines show the expected Keplerian velocities taking into account the altitude of the ¹²CO and ¹³CO layers. The red and blue solid lines display the velocity of the ¹²CO and ¹³CO layers taking into account the altitude and the pressure gradient term, as derived from our MCFOST model. Right: circles and triangles represent the temperature measured on the upper and lower surfaces, respectively. The brightness temperatures are similar on the upper and lower surfaces for ¹³CO and C¹⁸O; for clarity, only the upper surface is plotted.