Model fit to the calibrated closure phases of the HD 90823 (binary) system. Top: closure phases of HD 90823 inferred from the central component in frame 25 (out of 49 frames) in the Hn5 filter. The closure phases of HD 90700 (point source) are averaged over all frames. Middle: calibrated observation, obtained by subtracting the closure phases of the point source from the closure phases of the binary. The best-fit model that was found is overplotted, with the corresponding χ² value reported in the legend. Bottom: residuals left after subtracting the model from the observation.