HD 217786
HD 217786 is a binary star system in the equatorial constellation of Pisces. With an apparent visual magnitude of 7.78, 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. Kinematically, the star system belongs to the thin disk population of the Milky Way.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Pisces |
| Right ascension | 23h 03m 08.20704s |
| Declination | −00° 25′ 46.6777″ |
| Apparent magnitude (V) | 7.78 |
| Characteristics | |
| Spectral type | F8V |
| B−V color index | 0.578±0.004 |
| Astrometry | |
| Radial velocity (Rv) | +10.00±0.02 km/s |
| Proper motion (μ) | RA: −89.933 mas/yr Dec.: −168.781 mas/yr |
| Parallax (π) | 17.9946 ± 0.0793 mas |
| Distance | 181.3 ± 0.8 ly (55.6 ± 0.2 pc) |
| Absolute magnitude (MV) | 4.09 + 11.02±0.13 |
| Details | |
| A | |
| Mass | 1.02 M☉ |
| Radius | 1.32±0.06 R☉ |
| Luminosity | 1.93±0.04 L☉ |
| Surface gravity (log g) | 4.13±0.02 cgs |
| Temperature | 5,882±8 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 M☉ |
| Other designations | |
| 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. It has about the same mass as the Sun but a 32% larger radius. The star is radiating nearly double the luminosity of the Sun from its photosphere at an effective temperature of 5,882 K.
A low-mass stellar companion at a projected separation of 155 AU was discovered in 2016. 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. No other companion stars have been detected at separations from 2.74 to 76.80 AUs.
The star system exhibits strong stellar flare activity in the ultraviolet.