The conjectured S-type retrograde planet in ν Octantis: more evidence including four years of iodine-cell radial velocities

Ramm, D. J. and Nelson, B. E. and Endl, M. and Hearnshaw, J. B. and Wittenmyer, R. A. and Gunn, F. and Bergmann, C. and Kilmartin, P. and Brogt, E. (2016) The conjectured S-type retrograde planet in ν Octantis: more evidence including four years of iodine-cell radial velocities. Monthly Notices of the Royal Astronomical Society, 460 (4). pp. 3706-3719. ISSN 0035-8711

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We report 1212 radial-velocity (RV) measurements obtained in the years 2009–2013 using an iodine cell for the spectroscopic binary ν Octantis (K1 III/IV). This system (abin ∼ 2.6 au, P ∼ 1050 d) is conjectured to have a Jovian planet with a semimajor axis half that of the
binary host. The extreme geometry only permits long-term stability if the planet is in a retrograde orbit. Whilst the reality of the planet (P ∼ 415 d) remains uncertain, other scenarios (stellar variability or apsidal motion caused by a yet unobserved third star) continue to appear
substantially less credible based on cross-correlation function bisectors, line-depth ratios and many other independent details. If this evidence is validated but the planet is disproved, the claims of other planets using RVs will be seriously challenged. We also describe a significant revision to the previously published RVs and the full set of 1437 RVs now encompasses nearly 13 yr. The sensitive orbital dynamics allow us to constrain the 3D architecture with a broad prior probability distribution on the mutual inclination, which with posterior samples obtained from an N-body Markov chain Monte Carlo is found to be 152. ◦ 5±0.7 0.6. None of these samples are dynamically stable beyond 106 yr. However, a grid search around the best-fitting solution
finds a region that has many models stable for 107 yr, and includes one model within 1σ that is stable for at least 108 yr. The planet’s exceptional nature demands robust independent verification and makes the theoretical understanding of its formation a worthy challenge.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to Published version allowed due to publisher copyright policy.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 16 Mar 2017 04:34
Last Modified: 16 Mar 2017 04:38
Uncontrolled Keywords: radial velocities; planets and satellites; dynamical evolution and stability; binaries; stars; ν Octantis.
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.1093/mnras/stw1106

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