Epsilon Cygni
| 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 | |
| Evolutionary stage | Horizontal branch |
| 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) | 53.693+0.321 −0.328 yr |
| Semi-major axis (a) | 15.8±0.2 AU |
| Eccentricity (e) | 0.9295±0.0003 |
| Argument of periastron (ω) (primary) | 275.30±0.06° |
| Semi-amplitude (K1) (primary) | 4.6 km/s |
| Details | |
| A | |
| Mass | 1.103±0.042 M☉ |
| Radius | 11.13 R☉ |
| Luminosity | 56.4±0.6 L☉ |
| Surface gravity (log g) | 2.79±0.23 cgs |
| Temperature | 4,699 K |
| Metallicity [Fe/H] | −0.126 dex |
| Rotation | 0.67 years |
| Rotational velocity (v sin i) | 2.3 ± 0.2 km/s |
| Age | 9.62±0.12 Gyr |
| B | |
| Mass | ≥0.265±0.007 M☉ |
| Other designations | |
| Aljanah, Gienah, ε Cyg, 53 Cygni, BD+33°4018, FK5 780, GCTP 4959.00, Gl 806.1, HD 197989, HIP 102488, HR 7949, LHS 5358, SAO 70474, WDS 20462+3358 | |
| Database references | |
| SIMBAD | data |
Epsilon Cygni (ε Cygni, abbreviated Epsilon Cyg, ε Cyg) is a binary star in the constellation of Cygnus. With an apparent visual magnitude of 2.48, it is readily visible to the naked eye at night, and is the third-brightest star in the constellation. Based upon parallax measurement, Epsilon Cygni is about 73 light-years distant.
The system has two confirmed constituents, Epsilon Cygni Aa (officially named Aljanah /ˈældʒənə/) and Ab. Additionally, a visual companion (Epsilon Cygni C) is likely bound to the system.