| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h 06m 21.76743s[2] |
| Declination | +35° 58′ 20.8875″[2] |
| Apparent magnitude (V) | 5.38[3] |
| Characteristics | |
| Evolutionary stage | subgiant[4] |
| Spectral type | G8.5 IVa[5] |
| B−Vcolor index | +0.85[3] |
| Variable type | RS CVn[6] |
| Astrometry | |
| Radial velocity (Rv) | −32.98±0.09[7] km/s |
| Proper motion (μ) | RA: −225.032[2]mas/yr Dec.: −440.042[2]mas/yr |
| Parallax (π) | 41.7718±0.0845 mas[2] |
| Distance | 78.1 ± 0.2 ly (23.94 ± 0.05 pc) |
| Absolute magnitude (MV) | 3.48[3] |
| Details[7] | |
| Mass | 1.26±0.03 M☉ |
| Radius | 2.51±0.05 R☉ |
| Luminosity | 4.07+0.50 −0.44 L☉ |
| Surface gravity (log g) | 3.74±0.07 cgs |
| Temperature | 5,108±26 K |
| Metallicity[Fe/H] | −0.02±0.05 dex |
| Rotational velocity (v sin i) | 1.78±0.23 km/s |
| Age | 4.34±0.40 Gyr |
| Other designations | |
| b1 Cygni,27 Cygni,V2008 Cygni,BD+35°3959,HD 191026,HIP 99031,HR 7689,SAO 69413,WDS J20064+3558A[8] | |
| Database references | |
| SIMBAD | data |
27 Cygni is asubgiantstar in the northernconstellation ofCygnus. It is faintly visible to thenaked eye with anapparent visual magnitude of 5.38.[3] The distance to this system, as estimated from its annualparallax shift of41.77 mas,[2] is 78.1 light-years. At that distance, the visual magnitude is diminished by anextinction of 0.05 due tointerstellar dust.[7] It is moving closer to the Earth with a heliocentricradial velocity of −33 km/s,[7] and has a relatively highproper motion, traversing thecelestial sphere at the rate of0.495″ per year.[9]
27 Cygni is aG-type subgiant with astellar classification of G8.5 IVa,[5] a star that has used up its corehydrogen and is starting to expand. It was found to be slightly variable by Percy et al. (1986), changing by up to 0.05 in visual magnitude with a characteristic time scale of 50–60 days.[10] Further observations suggested a possible rotation period of around 42 days.[11] Samus et al. (2017) classify it as a suspectedRS Canum Venaticorum variable, meaning that it is a close binary star whose components havestar-spots that causerotationally-modulated variations in brightness. It has been given thevariable star designation V2008 Cygni.[6]
27 Cygni is listed inmultiple star catalogues with three faint companions within onearc-minute.[12] The two closer ones are unrelated background objects, while the third has a similar distance and space motion and is described as a common proper motion companion.[13]
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