Disk-integrated spectral index α_{1 − 3 mm} vs. the cavity radius for two different kind of models: (1) dust evolution in a disk holding a 1 M_Jup located at different distances and created different cavity size (stars in the plot). For this case, the best linear fit to this model is also plotted (dashed line). (2) Models without considering dust evolution, but a dust-rich disk, assuming a power-law grain size distribution (n(a) ∝ a^− s), with a_min = 1 μm, a_max given by Eq. (3), three different values for s (s = 3.0, square points; s = 3.5 triangle points, and s = 4.0 circle points), and different truncated radii. The 1 and 2 σ regions from observations (Fig. 2) are also plotted.