Dynamical analysis and constraints for the HD 196885 system

¹ Department of Physics, I3NUniversity of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
e-mail: cristian@ua.pt
² Astronomie et Systèmes Dynamiques, IMCCE-CNRS UMR8028, 77 av. Denfert-Rochereau, 75014 Paris, France
³ Centro de Astrofísica, Universidade do Porto, rua das Estrelas, 4150-762 Porto, Portugal

Received: 28 October 2011
Accepted: 23 March 2012

Abstract

The HD 196885 system is composed of a binary star and a planet orbiting the primary. The orbit of the binary is fully constrained by astrometry, but for the planet the inclination with respect to the plane of the sky and the longitude of the node are unknown. Here we perform a full analysis of the HD 196885 system by exploring the two free parameters of the planet and choosing different sets of angular variables. We find that the most likely configurations for the planet are either nearly coplanar orbits (prograde and retrograde), or highly inclined orbits near the Lidov-Kozai equilibrium points, i = 44° or i = 137°. Among coplanar orbits, the retrograde ones appear to be less chaotic, while for the orbits near the Lidov-Kozai equilibria, those around ω = 270° are more reliable, where ${\mathit{\omega }}_{}$ is the argument of pericenter of the planet’s orbit with respect to the binary’s orbit . From the observer’s point of view (plane of the sky) stable areas are restricted to (I₁,Ω₁) ~ (65°,80°), (65°,260°), (115°,80°), and (115°,260°), where I₁ is the inclination of the planet and Ω₁ is the longitude of ascending node.