Predicted flux density of the dust continuum at 1.3 mm (open circles) and 3.2 mm (filled triangles) as a function of the uv distance averaged every 25 kλ for different ALMA antenna configurations. The corresponding spectral index α is shown with the blue line. Values are given on the right y-axis. The dashed blue line indicates α values corrected for the central regions (average flux around 200 kλ removed).