Orbital solutions to the HD160691 (mu Arae) Doppler signal

Abstract

We perform a dynamical analysis of the recently updated set of the radial velocity (RV) measurements of the HD160691 (mu Arae). The kinematic, 2-Keplerian model of the measurements leads to the best-fit solution in which the eccentricity of the outer planet is about 0.7 and its semi-major axis is about 4AU. The parameters of the inner planet are well determined. The eccentricity is about 0.3 and the semi-major axis is about 1.65AU. The best 2-Keplerian model leads to a catastrophically unstable configuration, self disrupting in less than 20,000yr. To derive dynamically stable configurations which are simultaneously consistent with the RV data, we use the so called GAMP (Genetic Algorithm with MEGNO Penalty). Using this method, we derive meaningful limits on the parameters of the outer planet which provide a stable behavior of the system. The best-fit solutions are located in a shallow valley of Chi^2, in the (a_c,e_c)-plane, extending over 2AU (for the formal 1sigma confidence interval of the best fit). We find two equally good best-fit solutions leading to the qualitatively different orbital configurations. One of them corresponds to the center of the 5:1 mean motion resonance (MMR) and the second one describes a configuration between the 6:1 and 17:2MMRs. The mu Arae system can be found in the zone confined to other low-order MMRs of the type p:1 with p>5. Our results support the classification of the mu Arae as a hierarchical planetary system, dynamically similar to other known multi-planet systems around HD12661 and HD169830. The results of the GAMP on the extended data set are fully consistent with our previous conclusions concerning a much shorter observational window.