χ² as function of P and e for the orbit of BC around A. The cross at P = 44.4 yr, e = 0.52 marks the minimum. The contour lines encircle the 68% confidence region (which is a series of mostly unconnected patches), the 95%, and the 99.7% confidence region (corresponding to 1σ, 2σ, and 3σ in the case of normally distributed errors). The dashed line marks the stability limit for the system, only orbits below this line are long-term stable (see Sect. 5.1).