Dynamical Stability and Habitability of γ Cephei Binary-Planetary System

It has been suggested that the long-lived residual radial velocity variations observed in the precision radial velocity measurements of the primary of γ Cephei (HR8974, HD222404, HIP116727) are likely due to a Jupiter-like planet around this star (Hatzes et al. 2003). In this paper, the orbital dynamics of this plant is studied and also the possibility of the existence of a hypothetical Earth-like planet in the habitable zone of its central star is discussed. Simulations, which have been carried out for different values of the eccentricity and semimajor axis of the binary, as well as the orbital inclination of its Jupiter-like planet, expand on previous studies of this system and indicate that, for the values of the binary eccentricity smaller than 0.5, and for all values of the orbital inclination of the Jupiter-like planet ranging from 0◦ to 40◦, the orbit of this planet is stable. For larger values of the binary eccentricity, the system becomes gradually unstable. Integrations also indicate that, within this range of orbital parameters, a hypothetical Earth-like planet can have a long-term stable orbit only at distances of 0.3 to 0.8 AU from the primary star. The habitable zone of the primary, at a range of approximately 3.1 to 3.8 AU, is, however, unstable. Subject headings: binaries: close — celestial mechanics — planetary systems — planets and satellites: general — solar system: general