T Cygni
T Cygni is a binary star system in the northern constellation of Cygnus. It is a faint system but visible to the naked eye with a combined apparent visual magnitude of 4.93. Based upon an annual Parallax shift of 8.4 mas, it is located 387 light years away. It is moving closer to the Earth with a heliocentric radial velocity of −24 km/s.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 20h 47m 10.75239s |
| Declination | +34° 22′ 26.8374″ |
| Apparent magnitude (V) | 4.93 + 10.03 |
| Characteristics | |
| Spectral type | K3 III |
| B−V color index | 1.294±0.003 |
| Variable type | Lb: |
| Astrometry | |
| Radial velocity (Rv) | −23.9±0.3 km/s |
| Proper motion (μ) | RA: +39.637 mas/yr Dec.: +8.068 mas/yr |
| Parallax (π) | 8.4327 ± 0.1348 mas |
| Distance | 387 ± 6 ly (119 ± 2 pc) |
| Absolute magnitude (MV) | −0.74 |
| Details | |
| A | |
| Radius | 28.19+0.67 −0.86 R☉ |
| Luminosity | 241.4±4.5 L☉ |
| Surface gravity (log g) | 2.12 cgs |
| Temperature | 4,285+50 −67 K |
| Metallicity [Fe/H] | −0.12 dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
The primary, component A, is a variable star, most likely of the slow irregular type, which ranges in magnitude from 4.91 down to 4.96. It is a giant star with a stellar classification of K3 III, which indicates it has exhausted the hydrogen at its core and evolved away from the main sequence. The star has expanded to 28 times the radius of the Sun. It is radiating 241 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,285 K.
The secondary companion, component B, is a magnitude 10.03 star located at an angular separation of 8.10″ along a position angle of 120°, as of 2012. In 1877 it was separated by 10.0″ with nearly the same position angle (121°).