Mu Cygni
μ Cygni, Latinised as Mu Cygni, is a binary star system in the northern constellation of Cygnus. It is visible to the naked eye as a faint point of light with a combined apparent visual magnitude of 4.49. The system is located 72 light years distant from the Sun, based on parallax, and is drifting further away with a radial velocity of +17 km/s.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 21h 44m 08.57767s |
| Declination | 28° 44′ 33.4567″ |
| Apparent magnitude (V) | 4.49 |
| Characteristics | |
| Spectral type | F6V + G2V |
| B−V color index | +0.512±0.007 |
| Astrometry | |
| Radial velocity (Rv) | +16.95 km/s |
| Proper motion (μ) | RA: +257.012 mas/yr Dec.: −239.009 mas/yr |
| Parallax (π) | 45.2207 ± 0.2383 mas |
| Distance | 72.1 ± 0.4 ly (22.1 ± 0.1 pc) |
| Absolute magnitude (MV) | 2.75 |
| μ1 Cyg | |
| Absolute magnitude (MV) | 2.77 |
| Absolute bolometric magnitude (Mbol) | 2.91±0.06 |
| μ2 Cyg | |
| Absolute magnitude (MV) | 4.38 |
| Absolute bolometric magnitude (Mbol) | 4.32±0.06 |
| Orbit | |
| Period (P) | 789 yr |
| Semi-major axis (a) | 5.32″ |
| Eccentricity (e) | 0.66 |
| Inclination (i) | 75.5° |
| Longitude of the node (Ω) | 110.1° |
| Periastron epoch (T) | 1958.0 |
| Argument of periastron (ω) (secondary) | 145.7° |
| Details | |
| μ1 Cyg | |
| Mass | 1.31 M☉ |
| Radius | 1.88±0.07 R☉ |
| Luminosity | 6.0 L☉ |
| Surface gravity (log g) | 3.93 cgs |
| Temperature | 6,354 K |
| Metallicity [Fe/H] | −0.16 dex |
| Rotational velocity (v sin i) | 11.6 km/s |
| Age | 3.46 Gyr |
| μ2 Cyg | |
| Mass | 0.99 M☉ |
| Radius | 1.08±0.05 R☉ |
| Luminosity | 1.4 L☉ |
| Surface gravity (log g) | 4.33 cgs |
| Temperature | 5.998 K |
| Metallicity [Fe/H] | −0.24 dex |
| Rotational velocity (v sin i) | 6.4 km/s |
| Age | 7.11 Gyr |
| Other designations | |
| μ1 Cyg: HD 206826, HR 8309, SAO 89940 | |
| μ2 Cyg: HD 206827, HR 8310, SAO 89939 | |
| Database references | |
| SIMBAD | μ Cyg |
| μ1 Cyg | |
| μ2 Cyg | |
The pair have an orbital period of around 800 years, with a semimajor axis of 5″ and an eccentricity around 0.6. The primary, with an apparent magnitude of 4.69, is an F-type main-sequence star with a stellar classification of F6V. It has 35% more mass than the Sun and 188% of the Sun's radius. The star is spinning with a projected rotational velocity of 9.6 km/s. The secondary companion, with an apparent magnitude of 6.12, is a G-type main-sequence star with a class of G2V. It has a similar radius as the Sun and slightly more mass.
Two reported additional components, C (apparent magnitude 12.93) and D (apparent magnitude 6.94), are believed to be optical doubles rather than part of the Mu Cygni system. Component D is the more distant spectroscopic binary HD 206874 (HIP 107326), consisting of two early F-type subgiants.