Bayesian evidence for two companions orbiting HIP 5158

We present results of a Bayesian analysis of radial velocity data for the star HIP 5158, confirming the presence of two companions and also constraining their orbital parameters. Assuming Keplerian orbits, the two-companion model is found to be e⁴⁸ times more probable than the one-planet model, although the orbital parameters of the second companion are only weakly constrained. The derived orbital periods are 345.6 ± 2.0 and 9017.8 ± 3180.7 d, respectively, and the corresponding eccentricities are 0.54 ± 0.04 and 0.14 ± 0.10. The limits on planetary mass (m sin i) and semimajor axis are (1.44 ± 0.14M_J, 0.89 ± 0.01 au) and (15.04 ± 10.55M_J, 7.70 ± 1.88 au), respectively. Owing to the large uncertainty on the mass of the second companion, we are unable to determine whether it is a planet or a brown dwarf. The remaining 'noise' (stellar jitter) unaccounted for by the model is 2.28 ± 0.31 m s^-1. We also analysed a three-companion model, but found it to be e⁸ times less probable than the two-companion model.