Long Term Stability of Planetary Orbits in the HD 59686 Eccentric Binary System

Abstract

Despite the large number of extrasolar planets discovered to date, only a few have been found in binary star systems. HD 59686 is special due to the detection of a planet orbiting the primary star of a close and highly eccentric binary system. The binary has orbital semimajor axis of 13.6 AU and eccentricity of 0.73, while the planet with a minimum mass of 7.0 Jupiter mass orbits the primary at 1.1 AU (Ortiz et al. 2016). According to the empirical stability criterion of Holman & Wiegert (1999), the planet may not be stable, if it is in a coplanar prograde orbit. We have explored the stability regions of planetary orbits using numerical orbit integrations of test particles in this binary system. For coplanar prograde orbits, there are extra stable regions beyond the circular stability boundary, if the planetary orbit is eccentric. They are stabilized by alignment with the binary orbit. Some of these stable regions are close to the orbit of the observed planet. For coplanar retrograde orbits, the circular stability boundary extends well beyond the orbit of the observed planet, but there are also extra stable regions due to alignment with the binary orbit.