A pair of Jovian planets at HD 202696

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A pair of Jovian planets at HD 202696

Post by Sirius_Alpha on 7th January 2019, 9:48 pm

Two Jovian planets around the giant star HD202696. A growing population of packed massive planetary pairs around massive stars?

We present evidence for a new two-planet system around the giant star HD\,202696 (= HIP\,105056, BD\,+26 4118). The discovery is based on public HIRES radial velocity measurements taken at Keck Observatory between July 2007 and September 2014. We estimate a stellar mass of 1.91+0.09−0.14M⊙ for HD\,202696, which is located close to the base of the red giant branch. A two-planet self-consistent dynamical modeling MCMC scheme of the radial velocity data followed by a long-term stability test suggests planetary orbital periods of Pb = 517.8+8.9−3.9 days and Pc = 946.6+20.7−20.9 days, eccentricities of eb = 0.011+0.078−0.011 and ec = 0.028+0.065−0.012 , and minimum dynamical masses of mb = 2.00+0.22−0.10\,MJup and mc = 1.86+0.18−0.23,MJup, 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, which 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.

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