68 Cygni
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 21h 18m 27.18622s |
| Declination | +43° 56′ 45.3992″ |
| Apparent magnitude (V) | 5.00 |
| Characteristics | |
| Spectral type | O7.5IIIn((f)) |
| U−B color index | −0.94 |
| B−V color index | −0.01 |
| Variable type | ELL |
| Astrometry | |
| Radial velocity (Rv) | 1 ± 5 km/s |
| Proper motion (μ) | RA: +4.632 mas/yr Dec.: −8.487 mas/yr |
| Parallax (π) | 1.4498±0.1152 mas |
| Distance | 2,200 ± 200 ly (690 ± 50 pc) |
| Absolute magnitude (MV) | −7.9 |
| Details | |
| Mass | 23 – 36+14 −10 M☉ |
| Radius | 15.7+2.3 −2.0 R☉ |
| Luminosity | 316,000+110,000 −82,000 L☉ |
| Surface gravity (log g) | 3.6+0.09 −0.08 cgs |
| Temperature | 34,000 K |
| Rotational velocity (v sin i) | 399 km/s |
| Other designations | |
| V1809 Cygni, A Cygni, HD 203064, HR 8154, BD+43 3877, HIP 105186, WDS J21185+4357 | |
| Database references | |
| SIMBAD | data |
68 Cygni is the Flamsteed designation for a star in the constellation Cygnus. Located approximately 690 parsecs (2,300 ly) distant, the star is a hot blue giant of spectral type O7.5IIIn((f)), a massive star that is likely currently expanding to become a supergiant. The star is surrounded by a ring-shaped nebula (likely a Strömgren sphere) named Sharpless 2-119 (Clamshell nebula).
68 Cygni is currently classified as a rotating ellipsoidal variable, varying between apparent magnitudes 4.98 and 5.09, although the classification as a rotating ellipsoidal variable is subject to controversy. Barely visible to the naked eye, the star is likely to have a mass of around 26 solar masses and a temperature of approximately 34,000 kelvins, although many of the star's physical parameters are subject to uncertainties due to the unclear nature of the system.