Epsilon Swan

Epsilon Cygni ( lat. Υ Cygni ) - a star in the northern constellation Cygni . Available for observation with the naked eye, the apparent magnitude is 4.43. ^[2] Based on the measured value of the annual parallax equal to 5.08 msd , ^{[1] an} estimate of the distance to the object is obtained - approximately 640 light years from the Sun.

Epsilon Swan is the star of the main sequence of the spectral class B2 Vne. ^[5] The index 'e' indicates that the object is a Be-star ; the star rotates rapidly and is surrounded by a rotating gas disk. The star has a high projection of the rotation speed - about 230 km / s, ^[3] as a result of which the lines in the spectrum have a blurred form, reflected in the classification by the index 'n'. The radiation region in the disk possesses a radius of 0.20 ± 0.04 au . ^[7] The star itself is observed almost from the pole, since absorption lines from the disk are almost not observed. ^[ten]

Epsilon Cygnus has a mass of 9.3 ^{[6] the} mass of the Sun and a radius of 4.7 ^{[7] of the} radius of the Sun. A quick rotation gives the star a flattened shape, the radius of the equator of the star is 18% more than the polar radius. ^[11] Luminosity exceeds solar by 7305 ^[6] times, effective temperature of the external atmosphere is 22000 K. ^[6]

The star exhibits luminosity variability, including short-period pulsations with periods of 2.95 and 2.6 peaks per day, as well as random flashes that occur every few years. Such outbreaks may be associated with moments of mass loss. The star may be a spectral binary , but the second component was not detected by speckle interferometry . Radial velocity variations can result from a companion object with a circulation period of about 11.4 years. ^[eleven]