| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Pisces[1] |
| Right ascension | 22h 58m 15.5408s[2] |
| Declination | −02° 23′ 43.383″[2] |
| Apparent magnitude (V) | +6.17[1] |
| Characteristics | |
| Evolutionary stage | subgiant[2] |
| Spectral type | G8 IV-V[1] |
| B−Vcolor index | 0.744±0.006[1] |
| Astrometry | |
| Radial velocity (Rv) | −13.4±0.1[1] km/s |
| Proper motion (μ) | RA: −6.819(25)mas/yr[2] Dec.: −15.040(23)mas/yr[2] |
| Parallax (π) | 49.7846±0.0263 mas[2] |
| Distance | 65.51 ± 0.03 ly (20.09 ± 0.01 pc) |
| Absolute magnitude (MV) | 4.68[1] |
| Details | |
| Mass | 1.045+0.018 −0.023[3] M☉ |
| Radius | 1.2245±0.0173[3] R☉ |
| Luminosity | 1.20[4] L☉ |
| Temperature | 5391±40[5] K |
| Metallicity | 0.31[5] |
| Rotation | 39.0 days[6] |
| Rotational velocity (v sin i) | 0.97[7] km/s |
| Age | 7.13[4] Gyr |
| Other designations | |
| 6 G. Piscium,BD−03°5539,FK5 3836,HD 217107,HIP 113421,HR 8734,SAO 146412,CCDM J22583-0224AB[8] | |
| Database references | |
| SIMBAD | data |
HD 217107 (6 G. Piscium) is ayellow subgiantstar approximately 65light-years away from Earth in theconstellation ofPisces (theFish). Its mass is very similar to theSun's, although it is considerably older. Two planets have been discovered orbiting the star: one is extremely close and completes an orbit every seven days, while the other is much more distant, taking fourteen years to complete an orbit.
HD 217107 is fairly close to the Sun: theGaiaastrometric satellite measured itsparallax as 49.7846milliarcseconds, which corresponds to a distance of 65.51light years.[2] Itsapparent magnitude is 6.17, making it just barely visible to thenaked eye under favourable conditions.
Spectroscopic observations show that itsspectral type is G7 or G8, which means its temperature is about5,400 K.[9] Its mass is roughly the same as the Sun's, although its estimated age of 7.1 billion years is somewhat older than the Sun's 4.6 billion years and it is thought to be evolving away from themain sequence, having consumed almost all thehydrogen in its core innuclear fusion reactions.[4][10][2]
A study of theradial 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 aplanetary companion in orbit around the star, with a minimum mass slightly greater than that ofJupiter.[9] The companion planet was designatedHD 217107 b.
While most planets with orbital periods of less than 10 days have almost circular orbits, HD 217107 b has a somewhateccentric 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 severalastronomical units (AU).[11] 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 ofJupiter in a very eccentric orbit with asemimajor axis of about 4.3 AU.[12] The second planet was designatedHD 217107 c.[13]
In 2025, the use ofastrometry allowed the inclinations and true masses of the planets to be found. The inclinations are nearly edge-on, so the minimum masses are close to the real ones.[3]
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | 1.446+0.180 −0.067 MJ | 0.07359+0.00042 −0.00053 | 7.12687±0 | 0.1284+0.0015 −0.0014 | 93+25 −26° | — |
| c | 4.37+0.13 −0.10 MJ | 5.922+0.035 −0.044 | 5,138±11 | 0.3918+0.0064 −0.0067 | 88+14 −12° | — |
