A pair of giant planets around the evolved intermediate-mass star hd 47366: multiple circular orbits or a mutually retrograde configuration

Sato, Bun’ei and Wang, Liang and Liu, Yu-Juan and Zhao, Gang and Omiya, Masashi and Harakawa, Hiroki and Nagasawa, Makiko and Wittenmyer, Robert A. and Butler, Paul and Song, Nan and He, Wei and Zhao, Fei and Kambe, Eiji and Noguchi, Kunio and Ando, Hiroyasu and Izumiura, Hideyuki and Okada, Norio and Yoshida, Michitoshi and Takeda, Yoichi and Itoh, Yoichi and Kokubo, Eiichiro and Ida, Shigeru (2016) A pair of giant planets around the evolved intermediate-mass star hd 47366: multiple circular orbits or a mutually retrograde configuration. The Astrophysical Journal, 819 (1). ISSN 0004-637X

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We report the detection of a double planetary system around the evolved intermediate-mass star HD 47366 from precise radial-velocity measurements at the Okayama Astrophysical Observatory, Xinglong Station, and Australian Astronomical Observatory. The star is a K1 giant with a mass of 1.81 ± 0.13 Me, a radius of 7.30 ± 0.33 Re, and
solar metallicity. The planetary system is composed of two giant planets with minimum masses of

1.75 +0.20 to -0.17 MJ

1.86 +0.16 to -0.15 MJ,

orbital periods of 363.3 +2.5 to -2.4 days

and 684.7 +5.0 to -4.9 days

and eccentricities of 0.089 +0.079 to -0.060

and 0.278 +0.067 to -0.094,

respectively, which are derived by a double Keplerian orbital fit to the radial-velocity data. The system adds to the population of multi-giant-planet systems with relatively small orbital separations, which are preferentially found around evolved intermediate-mass stars. Dynamical stability analysis for the system revealed, however, that the best-fit orbits are unstable in the case of a prograde configuration. The system could be stable if the planets were in 2:1 mean-motion resonance, but this is less likely, considering the observed period ratio and eccentricity. A present possible scenario for the system is that both of the planets have nearly circular orbits, namely the eccentricity of the outer planet is less than ∼0.15, which is just within 1.4σ of the best-fit value, or the planets are in a mutually retrograde configuration with a mutual orbital inclination larger than 160°.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Published version made accessible, in accordance with the copyright policy of the publisher.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 20 Mar 2017 07:01
Last Modified: 24 Mar 2017 02:51
Uncontrolled Keywords: stars; HD 47366; techniques; radial velocities
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: 10.3847/0004-637X/819/1/59
URI: http://eprints.usq.edu.au/id/eprint/30649

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