On the Extrasolar Multiplanet System around HD 160691

We reanalyze the precision radial velocity (RV) observations of HD 160691 (k 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 (6630 days and 62500 days, respectively) and a hot Neptune (HD 160691d) in 69 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 6307 day orbit. Overall, the global architecture of four-planet configuration recalls the solar system. All companions of k 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 6 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.