Dynamical analysis of the 5:1 mean-motion resonance of the HD 202206 system

Abstract

The HD 202206 system, which features two substellar companions with a 5:1 period ratio around a solar-type star, offers a rare opportunity to study high-order mean-motion resonances and provides new insights into the formation and evolution of substellar companions in extrasolar planetary systems. We revisited the HD 202206 system, aiming to conduct a more comprehensive analysis of orbital inclinations, companion masses, resonance dynamics, and potential formation mechanisms. Our analysis of the astrometric jitter around the best fit in the Gaia DR3 catalog and the proper motion anomalies between Hipparcos and Gaia places robust constraints on the orbital inclinations. We performed a new dynamical fit to all available radial velocity data from the CORALIE and HARPS spectrographs. We assessed the dynamical configuration and long-term stability of the system using samples generated by nested sampling. Our analysis shows that the orbital inclinations are strongly constrained to about $51^{\circ }$. Consequently, the best-fit dynamical solution, assuming a coplanar and inclined ($i=51^{\circ }$) configuration, yields an inner brown dwarf of $21.56M_{\mathrm{J}}$ and an outer giant planet of $3.12M_{\mathrm{J}}$. The corresponding orbital periods are 256.26 days and 1298.87 days, with eccentricities of 0.426 and 0.180. An investigation of the five relevant resonance angles shows that only one is librating with a large amplitude. Our stability analysis confirms that the system is dynamically stable. Our results provide new constraints on the masses and inclination of the system, challenging earlier claims of a face-on configuration and shedding light on the formation and evolution of substellar companions in extrasolar planetary systems.

10 pages, 8 figures. Published in A&A

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