• methods: analytical;
  • techniques: radial velocities;
  • celestial mechanics;
  • planets and satellites: detection;
  • planets and satellites: dynamical evolution and stability;
  • binaries: spectroscopic


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 analyse the radial velocity data for ν-Octantis A which has a nearby companion (ν-Octantis B) and we obtain retrograde precession of −0bsl0006486 ± 0bsl0006402 yr−1. We show that if ν-Octantis B was itself a double star, it could mimic a signal with similarities to that previously identified as a planet of ν-Octantis A. Nevertheless, we need more observations in order to decide in favour of the double-star hypothesis.