Upper panel: two-dimensional a posteriori distribution of the argument of periastron ω vs. the eccentricity e as obtained with the MCMC method. The yellow filled circle corresponds to the best-fit orbital solution of Johnson et al. (2011), while the green circle indicates our best-fit values of the parameters. The orange level lines enclose 68.2, 95, and 99.7 per cent of the distribution, respectively. Individual points of the MCMC have been plotted after applying a thinning factor of 100 to the chain for clarity. Middle panel: as upper panel, but for the radial velocity semi-amplitude K and the eccentricity e. Lower panel: as upper panel, but for the argument of periastron ω and the radial velocity semi-amplitude K.