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Paper: ν Octantis: A Close Binary with a Possible Planet
Volume: 435, Binaries – Key to Comprehension of the Universe
Page: 435
Authors: Ramm, D. J.; Hearnshaw, J. B.
Abstract: A new astrometric-spectroscopic orbital solution for the single-lined K-giant binary ν Octantis (P = 2.9 yr, e = 0.2358±0.0003) has been derived based on 221 high-precision differential spectroscopic radial velocities (RVs) from 222 CCD spectra obtained with the Hercules spectrograph at Mt John and from Hipparcos astrometry. An inclination of i = 70.8 ± 0.9° has been derived, based on a spectroscopic solution and the Hipparcos astrometry. We have discovered low-amplitude periodic behaviour in the residuals of the orbital solution, with a semi-amplitude of 50 ms-1 and a 417-d period, which is coherent over several years. The RV curve of the perturbation is apparently in a 5:2 resonance with that of the binary. The possible causes of such a perturbation are pulsations, rotational modulation of a surface phenomenon or an orbiting body. We have carefully assessed these alternatives and conclude that both pulsation and a rotational modulation appear unlikely explanations. The data imply that a planetary mass is a realistic cause. The putative planet (M ∼2.5MJup) would have an orbit (e∼0.1, a3∼1.2 AU) about mid-way between the stars. This orbit, supposedly in resonance with the binary system, appears to be highly unlikely based on current planet formation and orbit-stability expectations. More observations and theoretical modeling are needed to confirm a planet.
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