On the extrasolar multi-planet system around HD160691
  We re-analyze the precision radial velocity (RV) observations of HD160691 (mu Ara) by the Anglo-Australian Planet Search Team. The star is supposed to host two Jovian companions (HD160691b, HD160691c) in long-period orbits about 630 days and about 2500 days, respectively) and a hot-Neptune (HD160691d) in about 9 days orbit. We perform a global search for the best fits in the orbital parameters 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, yet unconfirmed, Jupiter-like planet HD160691e in about 307 days orbit. Overall, the global architecture of four-planet configuration recalls the Solar system. All companions of mu 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 about 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. 
Krzysztof Gozdziewski, Andrzej J. Maciejewski and Cezary Migaszewski