9 Cygni
9 Cygni is a binary star system in the northern constellation of Cygnus. 9 Cygni is its Flamsteed designation. The two stars have a combined magnitude of 5.39, so it can be seen with the naked eye under good viewing conditions. Parallax measurements made by Gaia put the star at a distance of around 590 light-years (182 parsecs) away.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 19h 34m 50.9285s |
| Declination | +29° 27′ 46.697″ |
| Apparent magnitude (V) | 5.39 (5.9 + 6.4) |
| Characteristics | |
| Evolutionary stage | Red clump + main sequence |
| Spectral type | G8 IIIa + A2 V |
| B−V color index | 0.581 |
| Astrometry | |
| Radial velocity (Rv) | 20.09±1.98 km/s |
| Proper motion (μ) | RA: +14.822 mas/yr Dec.: +13.554 mas/yr |
| Parallax (π) | 5.4904 ± 0.0892 mas |
| Distance | 594 ± 10 ly (182 ± 3 pc) |
| Absolute magnitude (MV) | −0.70 |
| Orbit | |
| Period (P) | 4.56 yr |
| Semi-major axis (a) | 0.030″ |
| Eccentricity (e) | 0.82 |
| Inclination (i) | 114.6° |
| Longitude of the node (Ω) | 29.3° |
| Periastron epoch (T) | 1985.56 |
| Argument of periastron (ω) (secondary) | 45.5° |
| Details | |
| 9 Cyg A | |
| Mass | 2.9±0.4 M☉ |
| Radius | 18.2 R☉ |
| Surface gravity (log g) | 3.040±0.370 cgs |
| Temperature | 5,047 K |
| Metallicity [Fe/H] | −0.260±0.090 dex |
| 9 Cyg B | |
| Mass | 2.7±0.4 M☉ |
| Radius | 3.5 R☉ |
| Temperature | 9,247 K |
| Age | 437.1 Myr |
| Other designations | |
| 9 Cyg A: HD 184759 | |
| 9 Cyg B: HD 184760 | |
| Database references | |
| SIMBAD | data |
The two stars of 9 Cygni are a G-type giant and an A-type star. Both stars are over twice as massive as the Sun. They orbit once every 4.56 years, separated with a semi-major axis of 0.030 arcseconds. However, the eccentricity is high, at 0.82. The primary is a red clump giant, a star on the cool end of the horizontal branch fusing helium in its core. The secondary star has begun to evolve off the main sequence; it is sometimes classified as a giant star and sometimes as a main-sequence star.