On the Extrasolar Multiplanet System around HD 160691

We reanalyze the precision radial velocity (RV) observations of HD 160691 (μ Ara) by the Anglo-Australian Planet Search Team. The star is supposed to host two Jovian companions (HD 160691b, HD 160691c) in long-period orbits (~630 days and ~2500 days, respectively) and a hot Neptune (HD 160691d) in ~9 day orbit. We perform a global search for the best fits in the orbital parameter space with a hybrid code employing the genetic algorithm and simplex method. The stability of Keplerian fits is verified with the N-body model of the RV signal that takes into account the dynamical constraints (so called GAMP method). Our analysis reveals a signature of the fourth, as yet unconfirmed, Jupiter-like planet HD 160691e in ~307 day orbit. Overall, the global architecture of four-planet configuration recalls the solar system. All companions of μ Ara move in quasi-circular orbits. The orbits of two inner Jovian planets are close to the 2 : 1 mean motion resonance. The alternative three-planet system involves two Jovian planets in eccentric orbits (e ~ 0.3), close to the 4 : 1 MMR, but it yields a significantly worse fit to the data. We also verify a hypothesis of the 1 : 1 MMR in the subsystem of two inner Jovian planets in the four-planet model.

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