χ² as function of period and eccentricity for the orbit of T Tau S around T Tau N. The cross marks the location of the best-fitting orbit solution (see Table 4). Contour lines show the 68.3% and 99.7% confidence regions (equivalent to 1σ and 3σ for a normal distribution). The innermost contour line is at . This has no particular significance, but demonstrates how flat χ² is around the minimum.