The parameters provided by the best model, obtained by fitting an elliptical Gaussian distribution to MIDI visibilities, as a function of wavelength: a) the FWHM of the major axis; b) the flattening (ratio of the FWHM of the minor axis to that of the major axis); c) the projection of the major axis (θ) on the sky plane; and d) the χ² for each wavelength. The dashed lines indicate the errors for each parameter as a function of the wavelength. The vertical solid lines represent the atmospheric ozone band.