Properties of the reference models. Top panel: dust surface density. The dust surface densities of model 1 and model 2 are the same. Middle panel: radial profile of the maximum grain size of model 1 (red line) and model 2 (blue line). The horizontal dashed line marks the 0.4 mm boundary defined in Fig. 1. Bottom panel: optical depth at the wavelength of 1.3 mm. The color coding is identical to that in the middle panel. The τ_1.3mm = 1 condition is indicated with the horizontal dashed line.