The CORALIE survey for southern extra-solar planets. XIII. A pair of planets around HD 202206 or a circumbinary planet?

Long-term precise Doppler measurements with the CORALIE spectrograph reveal the presence of a second planet orbiting the solar-type star HD 202206. The radial-velocity combined fit yields companion masses of m₂sin i=17.4 M_Jup and 2.44 M_Jup, semi-major axes of a=0.83 AU and 2.55 AU, and eccentricities of e=0.43 and 0.27, respectively. A dynamical analysis of the system further shows a 5/1 mean motion resonance between the two planets. This system is of particular interest since the inner planet is within the brown-dwarf limits while the outer one is much less massive. Therefore, either the inner planet formed simultaneously in the protoplanetary disk as a superplanet, or the outer Jupiter-like planet formed in a circumbinary disk. We believe this singular planetary system will provide important constraints on planetary formation and migration scenarios.