  | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 21h 14m 47.4916s |
| Declination | +38° 02′ 43.141″ |
| Apparent magnitude (V) | 3.65 - 3.75[1](3.80 / 6.69[2]) |
| Characteristics | |
| Spectral type | F2 IV + G0 V |
| U−Bcolor index | +0.03 / +0.09 |
| B−Vcolor index | +0.38 / +0.60 |
| Variable type | δ Sct[1] |
| Astrometry | |
| Radial velocity (Rv) | -21.1 km/s |
| Proper motion (μ) | RA: 195.75mas/yr Dec.: 410.03mas/yr |
| Parallax (π) | 47.80±0.61 mas |
| Distance | 68.2 ± 0.9 ly (20.9 ± 0.3 pc) |
| Orbit[3] | |
| Period (P) | 49.5240 years |
| Semi-major axis (a) | 0.92224 arcseconds |
| Eccentricity (e) | 0.24535 |
| Inclination (i) | 133.242 degrees° |
| Longitude of the node (Ω) | 161.343 degrees° |
| Periastronepoch (T) | 1938.5919 |
| Argument of periastron (ω) (secondary) | 116.416 degrees° |
| Details | |
| τ Cyg A | |
| Mass | 1.65[2] M☉ |
| Radius | 2.48[2] R☉ |
| Surface gravity (log g) | 3.87[2] cgs |
| Temperature | 6,600[2] K |
| Metallicity [Fe/H] | 0.05[2] dex |
| τ Cyg B | |
| Mass | 1.03[2] M☉ |
| Radius | 0.93[2] R☉ |
| Surface gravity (log g) | 4.52[2] cgs |
| Temperature | 5,670[2] K |
| Other designations | |
| τ Cygni,65 Cygni,BD+37°4240,HD 202444,HIP 104887,HR 8130,SAO 71121, GC 29723, CCDM J21148+3803AB. | |
| Database references | |
| SIMBAD | data |
| A | |
| B | |
Tau Cygni, Latinised fromτ Cygni, is abinary star system in the constellationCygnus, approximately 69light years away fromEarth.[4] This visual binary system has a period of 49.6 years.[2]
The main star, 4th magnitude GJ 822.1 A, is a yellowish whitesubgiant star of thespectral type F2IV. It therefore has a surface temperature of 6,000 to 7,500kelvins and is larger, hotter, and several times as bright as theSun.[5] Its companion, 6th magnitude GJ 822.1 B, is a yellowmain sequence star of the spectral type G0V. It is similar to the Sun in size, surface temperature, and luminosity.[6]
Tau Cygni is classified as aδ Scuti variable. The magnitude range is given as 3.65 to 3.75, which is the combined magnitude for both components, although the variable component is A.[1]