  More than 10% of extra-solar planets (EPs) orbit in a binary or multiple
stellar system. We investigated the motion of planets revolving in binary
systems in the frame of the particular case of the three body problem. We
carried out an analysis of the motion an EP revolving in a binary system by
following conditions; a) a planet in a binary system revolves around one of the
components (parent star), b) the distance between the star`s components is
greater than between the parent star and the orbiting planet (ratio of the
semi-major axes is a small parameter), c) the mass of the planet is smaller
than the mass of the stars, but is not negligible. The Hamiltonian of the
system without short periodic terms was used. We expanded the Hamiltonian in
terms of Legendre polynomial and truncated after the second order term
depending on only one angular variable. In this case the solution of this
system was obtained and the qualitative analysis of motion was produced. We
have applied this theory to real EPs and compared to the numerical integration.
Analyses of the possible regions of motion are presented. It is shown that the
case of the stable and unstable motion of the EPs are possible. We applied our
calculations to two binary systems hosting an EP and calculated the possible
values for their unknown orbital elements.
