Best-fitting orbit model if the orbit is constrained to be coplanar with the circumbinary disk (Sect. 3.1). The observed positions are marked by their error ellipses and lines connecting the observed and calculated position at the time of the observations. The new observations with NACO are marked by crosses. Their errors are too small to be discernible. The dash-dotted line indicates the line of nodes, the dashed line the periastron, and the arrow shows the direction of the orbital motion.