Modeled line ratio for the Herbig disk model (top), where the absence of a dusty inner disk (left), the PAH abundance with respect to the ISM (middle), and the fraction of large grains (right) are compared to the fiducial Herbig disk model with a 0.01 times drop in gas density inside 30 AU (blue). The bottom row shows the temperature at the τ = 1 surface for the ¹³CO J = 6−5 (solid) and J = 2−1 (dotted) transitions. Both ¹³CO lines are (moderately) optically thin inside the gas cavities of these models. Therefore, the midplane temperature is shown in this region. We note the difference in the temperature axes.