Orbital Solutions to the HD 160691 (μ Arae) Doppler Signal

Abstract

We perform a dynamical analysis of the recently updated set of the radial velocity (RV) measurements of HD 160691 (μ Arae). The kinematic, double-Keplerian model of the measurements leads to a best-fit solution that is unstable and self-disrupting in less than 20,000 yr. In order to derive dynamically stable configurations that 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 that also provide a stable behavior of the system. The best-fit solutions are located in a shallow valley of (Χv 22)1/2 in the (ac, ec)-plane, extending over 2 AU (for the formal 1 σ confidence interval of the best fit). We find two equally good best-fit solutions leading to 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 11:2 and 17:3 MMRs. If the formal best-fit errors of the orbital parameters are taken into account, the HD 160691 system can likely be found in the zone of the phase space filled with low-order MMRs of the type p:1, with 5 < p < 15. Our results support the classification of μ Ara as a hierarchical planetary system, dynamically similar to other known multiplanet systems around HD 12661 and HD 169830. The results of the GAMP analysis on the extended data set are fully consistent with our previous conclusions concerning a much shorter observational window. This constitutes a valuable confirmation that the applied method is well suited for the analysis of RV data series that only partially cover the longest orbital period. © 2005. The American Astronomical Society. All rights reserved.