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Upsilon Cygni

Star in the constellation Cygnus From Wikipedia, the free encyclopedia

Upsilon Cygni
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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.

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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]

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