Upsilon Cygni

Not to be confused with Y Cygni.

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.

Upsilon Cygni

A light curve for Upsilon Cygni. The main figure, plotted from Hipparcos data,[1] shows the long-term variability, and the inset figure, plotted from TESS data,[2] shows the short-term variability.
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Cygnus
Right ascension	21h 17m 55.08585s[3]
Declination	+34° 53′ 48.7255″[3]
Apparent magnitude (V)	4.43[4]
Characteristics
Spectral type	B2 Vne[5]
U−B color index	−0.82[4]
B−V color index	−0.11[4]
Astrometry
Radial velocity (Rv)	−1.93±0.59[6] km/s
Proper motion (μ)	RA: +5.667[3] mas/yr Dec.: −5.601[3] mas/yr
Parallax (π)	5.0120±0.1891 mas[3]
Distance	650 ± 20 ly (200 ± 8 pc)
Absolute magnitude (MV)	−2.03[7]
Details
Mass	9.25±0.52[8] M☉
Radius	4.7[9] R☉
Luminosity (bolometric)	7,305[8] L☉
Surface gravity (log g)	3.30±0.10[10] cgs
Temperature	22,000[8] K
Metallicity [Fe/H]	−0.36[7] dex
Rotational velocity (v sin i)	230±24[6] km/s
Age	17.0±2.8[11] Myr
Other designations
υ Cyg, 66 Cygni, BD+34°4371, FK5 1559, HD 202904, HIP 105138, HR 8146, SAO 71173[12]
Database references
SIMBAD	data

This is a B-type main sequence star with a stellar classification of B2 Vne.^[5] 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,^[6] 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.^[9] 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^[8] times the mass of the Sun and is 4.7^[9] 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.^[10] It is radiating 7,305^[8] times the solar luminosity from its outer atmosphere at an effective temperature of 22,000 K.^[8]

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.^[10] Several stars appear close to it in the sky, but they are likely optical companions.^[14]