HD 217786
Binary star system in the constellation Pisces
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HD 217786 is a binary star[4] system in the equatorial constellation of Pisces. With an apparent visual magnitude of 7.78,[1] it requires binoculars or a small telescope to view. The system is located at a distance of 181 light-years from the Sun based on parallax, and is drifting further away with a radial velocity of +10 km/s.[1] Kinematically, the star system belongs to the thin disk population of the Milky Way.[7]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Pisces[1] |
| Right ascension | 23h 03m 08.20704s[2] |
| Declination | −00° 25′ 46.6777″[2] |
| Apparent magnitude (V) | 7.78[1] |
| Characteristics | |
| Spectral type | F8V[3] |
| B−V color index | 0.578±0.004[1] |
| Astrometry | |
| Radial velocity (Rv) | +10.00±0.02[1] km/s |
| Proper motion (μ) | RA: −89.933[2] mas/yr Dec.: −168.781[2] mas/yr |
| Parallax (π) | 17.9946±0.0793 mas[2] |
| Distance | 181.3 ± 0.8 ly (55.6 ± 0.2 pc) |
| Absolute magnitude (MV) | 4.09[1] + 11.02±0.13[4] |
| Details[5] | |
| A | |
| Mass | 1.02 M☉ |
| Radius | 1.32±0.06 R☉ |
| Luminosity | 1.93±0.04[6] L☉ |
| Surface gravity (log g) | 4.13±0.02 cgs |
| Temperature | 5,882±8[7] K |
| Metallicity | −0.19±0.01 |
| Rotational velocity (v sin i) | 1.18±0.05 km/s |
| Age | 9.40±0.22 Gyr |
| HD 217786 B | |
| Mass | 0.1622+0.0071 −0.0068[4] M☉ |
| Other designations | |
| BD−01°4382, HD 217786, HIP 113834, TYC 5242-591-1, GSC 05242-00591, 2MASS J23030822-0025465, Gaia DR2 2650902026099857920[8] | |
| Database references | |
| SIMBAD | data |
The primary is an F-type main-sequence star with a stellar classification of F8V. It is much older than Sun with an estimated age of 9.4 billion years and is spinning slowly with a projected rotational velocity of 1.2 km/s. The star has a lower proportion of heavy elements than the Sun, having 65% of solar abundance.[7] It has about the same mass as the Sun but a 32% larger radius.[5] The star is radiating nearly double[6] the luminosity of the Sun from its photosphere at an effective temperature of 5,882 K.[7]
A low-mass stellar companion at a projected separation of 155 AU was discovered in 2016.[4] The proper motion of this co-moving object suggests it is gravitationally-bound to the primary, and their orbit is being viewed edge-on. If the orbit is assumed to be circular, then the orbital period for the pair is ~6.2 Myr.[4] No other companion stars have been detected at separations from 2.74 to 76.80 AUs.[6]
The star system exhibits strong stellar flare activity in the ultraviolet.[9]
Planetary system
In 2010 one superjovian planet or brown dwarf on an eccentric orbit was discovered utilising the radial velocity method.[10] Designated component Ab, the high eccentricity of this object may have been caused by interaction with the secondary star.[4] In 2022, the inclination and true mass of HD 217786 Ab were measured via astrometry, and a second planet was discovered orbiting closer to the star.[11]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| c | ≥0.023±0.002 MJ | 0.038±0.002 | 2.5+0.00010 −0.00005 |
— | — | — |
| b | 13.852+1.267 −1.311 MJ |
2.446+0.109 −0.119 |
1,301.4+1.2 −0.5 |
0.311+0.002 −0.003 |
69.767+0.601 −0.386° |
— |