Analysis of the temperature and column density distribution in the disk around IRAS 20126+4104. (a) PV diagram along the disk plane of the CH₃CN rotation temperature obtained by fitting the brightness temperature of selected transitions. The black solid squares mark the points used to derive T_rot as a function of radius (see text). (b) Same as panel a but for the CH₃CN column density. (c) Rotation temperature versus angular radius obtained from the points of the PV diagram marked by the black solid squares. The solid line is a linear fit to the data corresponding to the relation T_rot(K) = 107 [θ(arcsec)]^−0.32. The dashed line corresponds to half the synthesized beam. (d) Same as panel c but for the CH₃CN column density. The relationship obtained from the linear fit to the data is N_col(cm⁻²) = 1.1 × 10¹⁵ [θ(arcsec)]^−1.3.