Stellar wobble caused by a nearby binary system: eccentric and inclined orbits

¹ Department of Physics, I3NUniversity of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
e-mail: helena.morais@ua.pt
² Astronomie et Systèmes Dynamiques, IMCCE-CNRS UMR 8028, 77 Avenue Denfert-Rochereau, 75014 Paris, France

Received: 16 April 2010
Accepted: 22 October 2010

Abstract

Most extrasolar planets currently known were discovered by means of an indirect method that measures the stellar wobble caused by the planet. We previously studied a triple system composed of a star and a nearby binary on circular coplanar orbits. We showed that although the effect of the binary on the star can be differentiated from the stellar wobble caused by a planet, because of observational limitations the two effects may often remain indistinguishable. Here, we develop a model that applies to eccentric and inclined orbits. We show that the binary’s effect is more likely to be mistaken by planet(s) in the case of coplanar motion observed equator-on. Moreover, when the orbits are eccentric, the magnitude of the binary’s effect may be larger than in the circular case. Additionally, an eccentric binary can mimic two planets with orbital periods in the ratio 2/1. However, when the star’s orbit around the binary’s center of mass has a high eccentricity and a reasonably well-constrained period, it should be easier to distinguish the binary’s effect from a planet.