Polar brightness maps of the systems n-i-M2 (same as in Fig. B.1a) and n-o-M4 at a wavelength of 2 µm (radius 400 au). The white asterisk denotes the position of the central star and defines the center of the coordinate system. The white crosses trace five lines of constant brightness (isophotes) and are drawn every 7.5°. The colored ellipses have been fitted to the respective isophotes using Eq. (4) with the central star in one of the focal points. The dashed lines give the direction from the focal point to the periapse, that is, ϕ + π, and are drawn in the same color as their corresponding ellipse.