N. Haghighipour (Inst. Astronomy/Univ. Hawaii)
Current models of planet formation explain how planets are formed around single stars. However, binary stars are the most common outcome of the star formation process. The discovery of extrasolar planets during the past decade has also provided strong evidence of planets in binary systems. Approximately 25% of all currently known extrasolar planet-hosting stars are members of binaries. Although almost all these binaries are wide with separations ranging from several hundreds to a thousand AU, there is considerable evidence for protoplanetary disks in young multiple star systems with smaller separations, and observations also show that initial conditions for planet formation exist in close binary systems, as well. Gamma cephei is a member of such binaries. A K1 IV subgiant, this star has a stellar companion at approximately 19 AU, and is orbited by a Jupiter-like planet with a semimajor axis of 2.13 AU. At such binary separations, the gravitational perturbation of the companion can have considerable effects on the structure of the circumstellar disk, formation of planetesimals and protoplanets, and ultimately on the formation of habitable planets around the planet-hosting star. In this paper, I will present the results of an extensive study of the dynamical stability of the gamma cephei binary-planetary system, and will review the issues regarding formation of planets in this binary. I will also discuss habitability in binary star systems, and will present the results of a large survey of the parameter space of gamma cephei in search of regions where habitable planets can have long-term stable orbits. Within the context of habitability, I will also discuss the effects of the companion on the formation of Earth-like planets in the habitable zone of gamma cephei system, and will also comment on the mechanisms of delivery of water to such planets.
This work is supported by the NASA Astrobiology Institute under the cooperative agreement NNA04CC08A at the Institute for Astronomy at the University of Hawaii.
Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.