Tau Cygni
Variable star in the constellation Cygnus
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Tau Cygni, Latinised from τ Cygni, also named Enduri Senggu (Manchu: ᡝᠨᡩᡠᡵᡳ ᠰᡝᠩᡤᡠ, Möllendorff: enduri senggu),[6] is a binary star system in the constellation Cygnus, approximately 69 light-years away from Earth.[4] This visual binary system has a period of 49.6 years.[3]
 | |
| Observation data Epoch J2000.0 Equinox ICRS | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 21h 14m 47.4925s[1] |
| Declination | +38° 02′ 43.144″[1] |
| Apparent magnitude (V) | 3.65 - 3.75[2] (3.80 / 6.69[3]) |
| Characteristics | |
| Spectral type | F2 IV[4] + G0 V[citation needed] |
| U−B color index | +0.03 / +0.09 |
| B−V color index | +0.38 / +0.60 |
| Variable type | δ Sct[2] |
| Astrometry | |
| Radial velocity (Rv) | −20.9[4] km/s |
| Proper motion (μ) | RA: +196.99 mas/yr[1] Dec.: +410.28 mas/yr[1] |
| Parallax (π) | 49.16±0.40 mas[1] |
| Distance | 66.3 ± 0.5 ly (20.3 ± 0.2 pc) |
| Absolute magnitude (MV) | 2.21 / 5.00[3] |
| Orbit[5] | |
| Period (P) | 49.5240 years |
| Semi-major axis (a) | 0.92224 |
| Eccentricity (e) | 0.24535 |
| Inclination (i) | 133.242° |
| Longitude of the node (Ω) | 161.343° |
| Periastron epoch (T) | 1938.5919 |
| Argument of periastron (ω) (secondary) | 116.416° |
| Details | |
| τ Cyg A | |
| Mass | 1.65[3] M☉ |
| Radius | 2.48[3] R☉ |
| Surface gravity (log g) | 3.87[3] cgs |
| Temperature | 6,600[3] K |
| Metallicity [Fe/H] | 0.05[3] dex |
| τ Cyg B | |
| Mass | 1.03[3] M☉ |
| Radius | 0.93[3] R☉ |
| Surface gravity (log g) | 4.52[3] cgs |
| Temperature | 5,670[3] K |
| Other designations | |
| Enduri Senggu, τ Cyg, 65 Cyg, BD+37°4240, GC 29723, GJ 822.1, GJ 9728, HD 202444, HIP 104887, HR 8130, SAO 71121, CCDM J21148+3803AB[4] | |
| Database references | |
| SIMBAD | data |
| A | |
| B | |
The main star, 4th magnitude GJ 822.1 A, is a yellowish white subgiant star of the spectral type F2IV. It therefore has a surface temperature of 6,000 to 7,500 kelvins and is larger, hotter, and several times as bright as the Sun.[7] Its companion, 6th magnitude GJ 822.1 B, is a yellow main sequence star of the spectral type G0V. It is similar to the Sun in size, surface temperature, and luminosity.[8]
Tau Cygni is classified as a δ 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.[2]
This star is part of the Manchu constellation Enduri Senggu, representing a hedgehog goddess.[10] The IAU Working Group on Star Names adopted the name Enduri Senggu for Tau Cygni A on 16 July 2026.[6]