Orbital motion of Ab (blue ellipse) around the system Aa (green ellipse). The size of the blue and green ellipses corresponds to the uncertainty of the astrometric position. The black solid ellipse corresponds to the orbital solution where both orbits are coplanar. The black dotted ellipse corresponds to the non-coplanar case. The red lines represent the periapsis, and the light-blue lines the distance from system Ab to the projected ellipses of the orbits.