2003A&A...399..773D

We use high angular and spectral resolution (∼1" & 0.1km/s) images in ¹²CO, ¹³CO J=2->1, J=1->0 and C¹⁸O J=2->1 coming from the IRAM interferometer to probe the vertical temperature distribution in the disk of DM Tau. We investigate here a new method based on the different opacities of the CO isotopomers to sample the temperature disk structure at various vertical scales inside the disk. Typically, the ¹²CO transitions are sampling at 2-4 scale heights, while the ¹³CO data are more likely tracing 1 scale height for the J=2-1, and the disk mid-plane for the J=1-0 line. At the disk scale at which the IRAM observations are sensitive (R≥50-60 AU), the analysis reveals a vertical temperature gradient. The outer layers where τ(¹²CO J=2-> 1) ≃1 are warmer (∼30K) than the inner layers probed by ¹³CO and C¹⁸O data (∼13-20K). These findings are consistent with the structure expected for flared irradiated disks around TTauri stars. We also observe that the outer radius of the disk is smaller in ¹³CO and C¹⁸O than in ¹²CO. These differences in truncation radius are in agreement with photodissociation effects. We also note that the dynamical mass determination from CO is weakly affected by the temperature gradient.