Mass ratio M_Sb/M_Sa as a function of the period of the T Tau N-S orbit model. These are the results of 150 runs of a Levenberg-Marquardt fit starting with different initial estimates for the parameters (see Sect. 3.2). The quantized appearance is caused by the grid-based fit method for the mass ratio. The large cross indicates the 68% confidence intervals for the period and mass ratio (see Tables 3 and 4). The models plotted encompass a wider range in period than the 68% confidence interval of the best solution.