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Precession due to a close binary system: an alternative explanation for ν-Octantis?

Authors

  • M. H. M. Morais,

    Corresponding author
    1. Department of Physics, I3N, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
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  • A. C. M. Correia

    Corresponding author
    1. Department of Physics, I3N, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
    2. Astronomie et Systèmes Dynamiques, IMCCE-CNRS UMR 8028, 77 Avenue Denfert-Rochereau, 75014 Paris, France
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E-mail: helena.morais@ua.pt (MHMM); correia@ua.pt (ACMC)

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 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.

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