Synthetic spectral energy distribution (SED) derived for the extended disc case, for two different spectral types for the primary: F5V (upper panel) and A3V (lower panel). For each case, two different e_b values, 0.3 and 0.75, are considered. The companion’s semi-major axis is given by the condition that the orbital stability limit is at a_crit = 4 AU, which leads to a_b = 16AU for the e_b = 0.3 run and a_b = 50AU for the e_b = 0.75 one. The respective contributions from r < a_crit and r > a_crit (“unstable”) grains are plotted. For the A3 case, we also plot the SED expected for a reference unperturbed annulus located at r = a_crit.