Upsilon Cygni
Star in the constellation Cygnus
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Upsilon Cygni is a star in the northern constellation of Cygnus. Its name is a Bayer designation that is Latinized from υ Cygni, and abbreviated Upsilon Cyg or υ Cyg. It is visible to the naked eye, having an apparent visual magnitude of 4.43. Based upon an annual parallax shift of 5.0 mas, it lies at a distance of roughly 650 light years from the Sun.
  | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Cygnus |
| Right ascension | 21h 17m 55.08585s[1] |
| Declination | +34° 53′ 48.7255″[1] |
| Apparent magnitude (V) | 4.43[2] |
| Characteristics | |
| Spectral type | B2 Vne[3] |
| U−B color index | −0.82[2] |
| B−V color index | −0.11[2] |
| Astrometry | |
| Radial velocity (Rv) | −1.93±0.59[4] km/s |
| Proper motion (μ) | RA: +5.667[1] mas/yr Dec.: −5.601[1] mas/yr |
| Parallax (π) | 5.0120±0.1891 mas[1] |
| Distance | 650 ± 20 ly (200 ± 8 pc) |
| Absolute magnitude (MV) | −2.03[5] |
| Details | |
| Mass | 9.25±0.52[6] M☉ |
| Radius | 4.7[7] R☉ |
| Luminosity (bolometric) | 7,305[6] L☉ |
| Surface gravity (log g) | 3.30±0.10[8] cgs |
| Temperature | 22,000[6] K |
| Metallicity [Fe/H] | −0.36[5] dex |
| Rotational velocity (v sin i) | 230±24[4] km/s |
| Age | 17.0±2.8[9] Myr |
| Other designations | |
| υ Cyg, 66 Cygni, BD+34°4371, FK5 1559, HD 202904, HIP 105138, HR 8146, SAO 71173[10] | |
| Database references | |
| SIMBAD | data |
This is a B-type main sequence star with a stellar classification of B2 Vne.[3] The 'e' suffix indicates this is a Be star, which means it is a rapidly rotating star surrounded by an orbiting gaseous disk. It has a high projected rotational velocity of about 230 km/s,[4] which accounts for the nebulous appearance of its lines as indicated by the 'n' suffix. The emission region of its disk has a radius of 0.20±0.04 AU.[7] The star itself is being viewed generally "pole-on", as ascertained by the lack of absorption features from the disk.[13]
Upsilon Cygni holds 9.3[6] times the mass of the Sun and is 4.7[7] times the Sun's radius. The rapid rotation is giving the star an oblate shape with an equatorial bulge that is 18% wider than the polar radius.[8] It is radiating 7,305[6] times the solar luminosity from its outer atmosphere at an effective temperature of 22,000 K.[6]
The star shows variations in luminosity, including short term non-radial pulsations with periods of 2.95 and 2.6 per day, as well as random outbursts occurring up to every few years. The latter may be associated with mass-loss episodes. There is suspicion this is a spectroscopic binary, but no companion has been detected via speckle interferometry. Measured variations in radial velocity may be caused by a companion having an orbital period of about 11.4 years.[8] Several stars appear close to it in the sky, but they are likely optical companions.[14]