Epsilon Cygni
Epsilon Cygni (ε Cygni, abbreviated Epsilon Cyg, ε Cyg) is multiple star system in the constellation of Cygnus. With an apparent visual magnitude of 2.48, it is readily visible to the naked eye at night as one of the brighter members of Cygnus. Based upon parallax measurement, Epsilon Cygni is about 73 light-years from the Sun.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h 46m 12.68236s |
| Declination | +33° 58′ 12.9250″ |
| Apparent magnitude (V) | 2.480 |
| Characteristics | |
| Spectral type | K0 III |
| U−B color index | +0.860 |
| B−V color index | +1.030 |
| Astrometry | |
| Radial velocity (Rv) | –12.41 km/s |
| Proper motion (μ) | RA: 355.66 mas/yr Dec.: 330.60 mas/yr |
| Parallax (π) | 44.86 ± 0.12 mas |
| Distance | 72.7 ± 0.2 ly (22.29 ± 0.06 pc) |
| Absolute magnitude (MV) | +0.74 ± 0.02 |
| Orbit | |
| Primary | ε Cyg Aa |
| Companion | ε Cyg Ab |
| Period (P) | 55.1 yr |
| Eccentricity (e) | 0.9 |
| Periastron epoch (T) | B2016.00 |
| Argument of periastron (ω) (primary) | 300° |
| Semi-amplitude (K1) (primary) | 4.0 km/s |
| Details | |
| Mass | ~2 M☉ |
| Radius | 10.82 ± 0.14 R☉ |
| Luminosity | 62 ± 3 L☉ |
| Surface gravity (log g) | 2.8 cgs |
| Temperature | 4,710 K |
| Metallicity [Fe/H] | –0.27 dex |
| Rotation | 0.67 years |
| Rotational velocity (v sin i) | 2.3 ± 0.2 km/s |
| Age | ~1.5 Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The system has three constituents: a spectroscopic binary (designated Epsilon Cygni A); an optical companion (B) and a single star (C). A's two components are themselves designated Epsilon Cygni Aa (officially named Aljanah /ˈældʒənə/) and Ab.
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