BI Cygni (BI Cyg, IRC +40408, BD+36 4025) is a

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 ...

in the constellation Cygnus. It is an irregular variable star with a maximum brightness of

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

8.4 and a minimum of magnitude 9.9. It is considered a member of the Cygnus OB1 stellar association, its distance is around of the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

. It is less than a degree south of another variable red supergiant, BC Cygni. BICygLightCurve

BI Cyg is a

slow irregular variable A slow irregular variable (ascribed the GCVS types L, LB and LC) is a variable star that exhibit no or very poorly defined periodicity in their slowly changing light emissions. These stars have often been little-studied, and once more is learnt a ...

star classified as type Lc, an irregular supergiant. Its brightness changes between extremes of

8.4 and 9.9. Frequency analysis of its

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

shows no significant periods. BI Cyg is one of the largest known stars with a radius around , measured by its

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the ''visual an ...

by the

CHARA array The CHARA (Center for High Angular Resolution Astronomy) array is an optical interferometer, located on Mount Wilson, California. The array consists of six telescopes operating as an astronomical interferometer. Construction was completed in ...

. It is about 90,000 times more luminous that the Sun and has a cool effective temperature of . Its mass is estimated at 17

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

es, and it took 12 million years to enter the

phase.

References

External links

INTEGRAL-OMC Catalogue of optically variable sources
{{Stars of Cygnus M-type supergiants Slow irregular variables Cygnus (constellation) Cygni, BI J20212192+3655555 IRAS catalogue objects Durchmusterung objects

See also

References

External links