Planetary System
A study of the radial velocity of HD 217107 carried out in 1998 revealed that its motion along the line of sight varied over a 7.1-day cycle. The period and amplitude of this variation indicated that it was caused by a planetary companion in orbit around the star, with a minimum mass slightly greater than that of Jupiter. The companion planet was designated HD 217107 b.
While most planets with orbital periods of less than 10 days have almost circular orbits, HD 217107 b has a somewhat eccentric orbit, and its discoverers hypothesized that this could be due to the gravitational influence of a second planet in the system at a distance of several astronomical units (AU). Confirmation of the existence of a second planet followed in 2005, when long term observations of the star's radial velocity variations revealed a variation on a period of about eight years, caused by a planet with a mass at least twice that of Jupiter in a very eccentric orbit with a semimajor axis of about 4.3 AU. The second planet was designated HD 217107 c.
| Companion |
Mass | Semimajor axis |
Orbital period |
Eccentricity | Radius |
|---|---|---|---|---|---|
| b | ≥ 1.39 ± 0.11 MJ | 0.0748 ± 0.0043 | 7.126816 ± 0.000039 | 0.1267 ± 0.0052 | — |
| c | ≥ 2.60 ± 0.15 MJ | 4.32 ± 0.38 | 3270 ± 220 | 0.517 ± 0.033 | — |
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