Squared visibility amplitudes as a function of wavelength of IRAS 13479-5436, IRAS 14086-6907, and IRAS 17020-5254 (from top to bottom). The blue dashed lines show the best-fit of a single component uniform disk model. The red solid lines indicate the best-fit two-component model consisting of a uniform disk describing the central source and a Gaussian disk describing the circumstellar dust shell. The fit parameters of the two-component model are indicated in Table 3.