Upsilon Cygni, Latinized from υ Cygni, is a

star A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...

in the northern constellation of Cygnus. It is visible to the naked eye, having an apparent visual magnitude of 4.43. Based upon an annual parallax shift of , it lies at a distance of roughly 650

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s from the Sun. This is a B-type main sequence star with a

stellar classification In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting t ...

of B2 Vne. 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 Stellar rotation is the angular motion of a star about its axis. The rate of rotation can be measured from the spectrum of the star, or by timing the movements of active features on the surface. The rotation of a star produces an equatorial bulge ...

of about 230 km/s, 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 . The star itself is being viewed generally "pole-on", as ascertained by the lack of absorption features from the disk. Upsilon Cygni holds 9.3 times the

mass of the Sun The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass of ...

and is 4.7 times the Sun's radius. The rapid rotation is giving the star an

oblate In Christianity (especially in the Roman Catholic, Orthodox, Anglican and Methodist traditions), an oblate is a person who is specifically dedicated to God or to God's service. Oblates are individuals, either laypersons or clergy, normally li ...

shape with an

equatorial bulge An equatorial bulge is a difference between the equatorial and polar diameters of a planet, due to the centrifugal force exerted by the rotation about the body's axis. A rotating body tends to form an oblate spheroid rather than a sphere. On Ear ...

that is 18% wider than the polar radius. It is radiating 7,305 times the

solar luminosity The solar luminosity (), is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nomin ...

from its outer atmosphere at an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 22,000 K. 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 The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

may be caused by a companion having an

orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...

of about 11.4 years. Several stars appear close to it in the sky, but they are likely optical companions.

References

{{Stars of Cygnus, state=collapsed B-type main-sequence stars Be stars Cygnus (constellation) Cygni, Upsilon Cygni, 66 Durchmusterung objects 202904 105138 8146