HD 59686 is a binary star system in the northern constellation of Gemini. It is visible to the naked eye as a dim point of light with an apparent visual magnitude of +5.45. The distance to this system is approximately 288 light-years based on parallax, but it is drifting closer with a radial velocity of −33 km/s.
This is a single-lined spectroscopic binary system with an orbital period of 32.0 years and a high eccentricity of 0.73. The visible component is an aging giant star with a stellar classification of K2III. It is most likely fusing helium in its core in a position on the H-R diagram called the red clump. The stellar radius is very large: 11.2 times that of the Sun. The star is around 2.7 billion years old with 1.4 times the mass of the Sun. It is radiating 58 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,670 K.
The secondary component has a minimum mass 53% that of the Sun, which indicates it must be a star rather than a brown dwarf or a planet.
Planetary system
The giant star HD 59686 A has one known planet, the gas giant HD 59686 Ab; it was discovered by Doppler spectroscopy and first announced in 2003, but the discovery was not formally published until 2016. HD 59686, along with Nu Octantis, is one of the closest binary star systems known to host a planet orbiting a single star.
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination (°) |
Radius |
|---|---|---|---|---|---|---|
| b | ≥6.92+0.18 −0.24 MJ |
1.0860+0.0006 −0.0007 |
299.36+0.26 −0.31 |
0.05+0.03 −0.02 |
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