* Astronomy

Title: Bayesian evidence for two companions orbiting HIP 5158
Authors: F. Feroz (Cambridge), S. T. Balan (Cambridge), M. P. Hobson (Cambridge)

We present results of a Bayesian analysis of radial velocity (RV) 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 e^{48} 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 d 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 ±0.14 M_{J}, 0.89 ±0.01 AU) and (15.04 ±10.55 M_{J}, 7.70 ±1.88 AU) respectively. Owing to 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. We also analysed a three-companion model, but found it to be e^{8} times less probable than the two-companion model.

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