Illustration of the radial brightness distribution (solid line) with auxiliary line (dotted line) used for the automatical gap detection. The corresponding simulated observation is shown in the upper right. The disk model has a scaling factor of k = 22 (outer disk radius 198 AU), a total disk mass of M = 2.67 × 10^-2 M_⊙, and a G type star (Sect. 3). We used the 8th ALMA configuration and a wavelength of 430 μm. A gap will be detected if the difference between the brightness profile and the auxiliary line at the local minimum of the brightness profile is three times larger than the standard deviation of the noise of the observation (noise: see Sect. 2.3 ).