Planetary System
In 2000, analysis of radial velocity measurements of the star revealed the existence of a substellar companion (designated HD 202206 b) with at least 17 times the mass of Jupiter around the star in an eccentric orbit with a period of around 256 days. This mass exceeds the 13 Jupiter mass limit above which an object can undergo deuterium fusion in its core, which some take to be the dividing line between planets and brown dwarfs, a definition which is supported by the IAU. However, some authors have suggested that the core accretion process (the traditional model for planet formation) can form objects above this limit, up to around 25–30 Jupiter masses. The classification of HD 202206 b as a brown dwarf or "superplanet" is currently unclear.
Even after HD 202206 b was accounted for, the star still showed a drift in the radial velocity measurements, indicating another companion in a longer-period orbit. In 2004 after further observations, the parameters of a companion was announced. This companion is about Jupiter's size, has a planetary mass at least 2.44 times that of Jupiter, and has an eccentric orbit taking around 1384 days to complete. The planet is located in a 5:1 orbital resonance with the inner companion.
The formation history of this planetary system is interesting: depending on the method of formation of the inner companion, the system can either be regarded as consisting of a superplanet and a planet, or alternatively a planet revolving in a circumbinary orbit.
| Companion |
Mass | Semimajor axis |
Orbital period |
Eccentricity | Radius |
|---|---|---|---|---|---|
| b | >17.4 MJ | 0.83 | 255.87 ± 0.06 | 0.435 ± 0.001 | — |
| c | >2.44 MJ | 2.55 | 1383.4 ± 18.4 | 0.267 ± 0.021 | — |
Read more about this topic: HD 202206
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