χ² as function of a and e for orbit models that are coplanar with the circumbinary disk (Sect. 3.1). The cross at a = 34   AU, e = 0.28 marks the minimum, the contour line around it encircles the 99.7% confidence region (corresponding to 3σ in the case of normally distributed errors). The areas in various shades of gray are within the 5σ confidence region, i.e. orbit models in the white area can be excluded with 5σ confidence.