KY Cygni is a variable

red supergiant Red supergiants (RSGs) are stars with a supergiant luminosity class ( Yerkes class I) and a stellar classification K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive or luminous. Betelg ...

spectral class 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 the ...

M3Ia located in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The first constellati ...

Cygnus. It is approximately 4,700

light-years A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by the International Astro ...

away.

Observations

KY Cyg lies near the bright

open cluster An open cluster is a type of star cluster made of tens 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, but is not thought to be a member. The location is close to the bright star

γ Cygni Gamma Cygni is a star in the northern constellation of Cygnus, forming the intersection of an asterism of five stars called the Northern Cross. It is officially named Sadr , gamma Cygni is its Bayer designation, which that is Latiniz ...

. 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 In astronomy, extinction is the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer. Interstellar extinction was first documented as such in 1930 by Robert Julius Trump ...

, 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 A stellar wind is a flow of gas ejected from the stellar atmosphere, upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spheri ...

. 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 MK ...

. 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 a 2020 paper published a luminosity of , which give a smaller radius of using 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 3,535K. 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.

Notes

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 Population I stars

Observations

Properties

See also

Notes

References

External links