KY Cygni is a red supergiant of spectral class M3.5Ia located in the constellation Cygnus. It is approximately 5,000

light-years 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 101 ...

away.

Observations

KY Cyg lies near the bright

open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

NGC 6913 Messier 29 or M29, also known as NGC 6913, is a quite small, bright open cluster of stars just south of the central bright star Gamma Cygni of a northerly zone of the sky, Cygnus. It was discovered by Charles Messier in 1764, and can be seen ...

, but is not thought to be a member. The location is close to the bright star γ Cygni. It was identified as a variable star in 1930, and later named as KY Cygni. The spectrum was given the MK classification of M3 Ia, with only minor adjustments since. KY Cygni is heavily reddened due to interstellar extinction, losing an estimated 7.75 magnitudes at visual wavelengths. It would be a naked eye star if no light was lost.

Properties

KY Cygni is classified as a luminous red supergiant with a strong stellar wind. It is losing mass at around and has been described as a cool

hypergiant A hypergiant (luminosity class 0 or Ia+) is a very rare type of star that has an extremely high luminosity, mass, size and mass loss because of its extreme stellar winds. The term ''hypergiant'' is defined as luminosity class 0 (zero) in the MKK ...

. Its properties are uncertain, but the temperature is around 3,500 K. A model fit based on K-band infrared brightness gives a luminosity of , corresponding to a radius of . Another model based on visual brightness gives an unexpectedly large luminosity of , with the difference due mainly to the assumptions about the level of extinction. The radius corresponding to the higher luminosity would be . These parameters are larger and more luminous than expected for any red supergiant, making them doubtful. More recently, integration of the

spectral energy distribution A spectral energy distribution (SED) is a plot of energy versus frequency or wavelength of light (not to be confused with a 'spectrum' of flux density vs frequency or wavelength). It is used in many branches of astronomy to characterize astron ...

s across a full range of wavelengths from U band to the 60 micron microwave flux gives an even lower luminosity of , and calculation of the bolometric luminosity based on its Gaia Data Release 2 parallax gives a luminosity below with a corresponding radius of . KYCygLightCurve

KY Cygni is a variable star with a large amplitude but no clear periodicity. At times, it varies rapidly, at others it is fairly constant for long periods. The photographic magnitude range is given as 13.5 - 15.5, while a visual range is 10.60 - 11.74.

References

External links

* http://jumk.de/astronomie/big-stars/ky-cygni.shtml * http://www.astronomy.com/asy/default.aspx?c=a&id=2772
List of Largest Stars Gets 3 New Chart Toppers
Robert Roy Britt, space.com, 10 January 2005. Accessed on line November 12, 2010. {{Stars of Cygnus M-type supergiants Cygnus (constellation) Slow irregular variables Cygni, KY J20255805+3821076 IRAS catalogue objects M-type hypergiants