Precession due to a close binary system: An alternative explanation for {\nu}-Octantis?

Abstract

We model the secular evolution of a star's orbit when it has a nearby binary system. We assume a hierarchical triple system where the inter-binary distance is small in comparison with the distance to the star. We show that the major secular effect is precession of the star's orbit around the binary system's centre of mass. We explain how we can obtain this precession rate from the star's radial velocity data, and thus infer the binary system's parameters. We show that the secular effect of a nearby binary system on the star's radial velocity can sometimes mimic a planet. We analyze the radial velocity data for {\nu}-octantis A which has a nearby companion ({\nu}-octantis B) and we obtain retrograde precession of (-0.86 \pm 0.02)\degree/yr. We show that if {\nu}-octantis B was itself a double star, it could mimic a signal with similarities to that previously identified as a planet of {\nu}-octantis A. Nevertheless, we need more observations in order to decide in favor of the double star hypothesis.