Gas temperature of our model for a T Tauri star and a PAH abundance of 0.001 with respect to the ISM (left), the fiducial Herbig model with a PAH abundance of 0.001 with respect to the ISM, and a Herbig model with a high PAH abundance of 0.1 with respect to the ISM (right). All models have a factor of 100 drop in gas density inside 30 AU. The cyan and orange contours indicate the τ = 1 surface of the ¹³CO J = 6−5 and J = 2−1 lines, respectively. The ¹³CO J = 2−1 transition is optically thin inside the dust cavity, and the J = 6−5 is optically thin inside the gas cavity, and hence these lines trace the midplane at these radii. We note that the dust cavity starts from 50 AU inward and the gas cavity from 30 AU. Only the regions with a gas density above 10⁷ cm⁻³ are shown.