Observations and modeling of DL Tau. Two models are plotted: the solid line is a model with R_c = 112 AU as observed in the dust and the dashed line as a model with R_c = 65, which fits the spatially resolved [C I] emission best. Further details can be found in the main text. 1σ error bars are indicated in gray for each spectrum. The data and models of the weak CO isotopologue J = 2−1 transitions have been multiplied by a factor of 5 for illustrative purposes.