Synthetic flux spectra (top) and visibility amplitude (bottom) based on the model parameters from Sec. 5.1 The simulation compares four different sets of dust shell parameters where only the optical depth of the silicate dust shell varies. The optical depth of an Al₂O₃ dust shell τ_V (Al₂O₃) is set to 3.0 and the optical depth of a silicate dust shell τ_V (silicate) is set to 0.0 (red), 0.7 (green), 1.5 (blue) and 3.0 (light blue). The full set of parameters can be found in the text.