摘要：We present evidence for a new two-planet system around the giant star HD202696 (=HIP 105056, BD +26 4118). The discovery is based on public HIRES radial velocity (RV) measurements taken at Keck Observatory between 2007 July and 2014 September. We estimate a stellar mass of - + M 1.91 0.14 0.09 for HD202696, which is located close to the base of the red giant branch. A two-planet self-consistent dynamical modeling MCMC scheme of the RV data followed by a long-term stability test suggests planetary orbital periods of P b = - + 517.8 3.9 8.9 and P c = - + 946.6 20.9 20.7 days, eccentricities of e b = - + 0.011 0.011 0.078 and e c = - + 0.028 0.012 0.065 , and minimum dynamical masses of m b = - + 2.00 0.10 0.22 and m c = - + 1.86 0.23 0.18 M Jup , respectively. Our stable MCMC samples are consistent with orbital configurations predominantly in a mean period ratio of 11:6 and its close-by high-order mean-motion commensurabilities with low eccentricities. For the majority of the stable configurations, we find an aligned or anti-aligned apsidal libration (i.e., Δω librating around 0° or 180°), suggesting that the HD 202696 system is likely dominated by secular perturbations near the high-order 11:6 mean-motion resonance. The HD 202696 system is yet another Jovian-mass pair around an intermediate-mass star with a period ratio below the 2:1 mean-motion resonance. Therefore, the HD 202696 system is an important discovery that may shed light on the primordial disk–planet properties needed for giant planets to break the strong 2:1 mean-motion resonance and settle in more compact orbits.
关键词：planetary systems;planets and satellites: detection;planets and satellites: dynamical evolution and stability;techniques: radial velocities
