A Pair of Giant Planets around the Evolved Intermediate-mass Star HD 47366: Multiple Circular Orbits or a Mutually Retrograde Configuration
Abstract
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 M⊙, a radius of 7.30 ± 0.33 R⊙, and solar metallicity. The planetary system is composed of two giant planets with minimum masses of {1.75}-0.17+0.20\quad {M}{{J}} and {1.86}-0.15+0.16\quad {M}{{J}}, orbital periods of {363.3}-2.4+2.5 days and {684.7}-4.9+5.0 days, and eccentricities of {0.089}-0.060+0.079 and {0.278}-0.094+0.067, 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°.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- March 2016
- DOI:
- 10.3847/0004-637X/819/1/59
- arXiv:
- arXiv:1601.04417
- Bibcode:
- 2016ApJ...819...59S
- Keywords:
-
- planetary systems;
- stars: individual: HD 47366;
- techniques: radial velocities;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- 11 pages, 9 figures, accepted for publication in ApJ