W Cephei is a

spectroscopic binary A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

and

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

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 ...

Cepheus Cepheus (Ancient Greek: Κηφεύς ''Kepheús'') may refer to: In Greek mythology * Cepheus (father of Andromeda), and King of Aethiopia * Cepheus (son of Aleus), a king of Tegea, Arcadia In astronomy * Cepheus (constellation), one of the 88 m ...

. It is thought to be a member of the Cep OB1

stellar association A stellar association is a very loose star cluster, looser than both open clusters and globular clusters. Stellar associations will normally contain from 10 to 100 or more visible stars. An association is primarily identified by commonalities in i ...

at about 8,000 light years. The supergiant primary star is one of the largest known stars and as well as one of the most luminous red supergiants.

Discovery

W Cephei was catalogued as BD+57°2568 in the

Bonner Durchmusterung In astronomy, Durchmusterung or Bonner Durchmusterung (BD) is an astrometric star catalogue of the whole sky, published by the Bonn Observatory in Germany from 1859 to 1863, with an extension published in Bonn in 1886. The name comes from ('run-t ...

published in 1903, and HD 214369 in the

Henry Draper Catalogue The ''Henry Draper Catalogue'' (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the ''Henry Draper Extension'' (HDE), published between 192 ...

. It was discovered to be a variable star by

T. H. E. C. Espin The Reverend Thomas Henry Espinell Compton Espin or T. H. E. C. Espin (28 May 1858 – 2 December 1934) was a British astronomer. His father Thomas Espin was Chancellor of the Diocese of Chester and his mother was Elizabeth (née Jessop). He ...

, in 1885. It was described in 1896 as a red star varying from magnitude 7.3 to 8.3. In 1925, W Cep was included in a listing of

Be star Be stars are a heterogeneous set of stars with B spectral types and emission lines. A narrower definition, sometimes referred to as ''classical Be stars'', is a non-supergiant B star whose spectrum has, or had at some time, one or more Balmer ...

s. It was recognised as a cool star with spectral type Mep. It was classified as K0ep Ia from a 1949 spectrum, but also recognised to have a small hot companion, plus an unusual infrared excess. Ultraviolet spectra allowed absorption lines from the companion to be studied and it was given a spectral type of B0-1.

System

The W Cephei system contains a luminous

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 ...

star with a non-supergiant early B companion. The star has unusual

emission lines A spectral line is a weaker or stronger region in an otherwise uniform and continuous spectrum. It may result from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used ...

including both permitted and forbidden Fe_II, produced by a circumstellar envelope containing dust and ionised gas. The two components have been resolved at using

speckle interferometry Speckle imaging comprises a range of high-resolution Astrophotography, astronomical imaging techniques based on the analysis of large numbers of short Exposure (photography), exposures that freeze the variation of Astronomical seeing, atmospheri ...

. An orbital period of 2,090 days has been proposed.

Variability

W Cephei varies in brightness from 7th to 9th magnitude. The

General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars in the Milky Way Galaxy. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR, edited by and Pavel Parenago. Second a ...

lists it as a

semiregular variable In astronomy, a semiregular variable star, a type of variable star, is a Red giant, giant or supergiant of intermediate and late (cooler) spectral type. It shows considerable periodicity in its light changes, accompanied or sometimes interrupted b ...

with a period of 370 days, but later attempts to find a period have shown only random variations. It has also been proposed that eclipses occur.

References

External links

AAVSO The American Association of Variable Star Observers (AAVSO) is an international nonprofit organization. Founded in 1911, the organization focuses on coordinating, analyzing, publishing, and archiving variable star observations made largely by amat ...

br>chart of comparison stars for W Cephei
*

British Astronomical Association The British Astronomical Association (BAA) was formed in 1890 as a national body to support the UK's amateur astronomers. Throughout its history, the BAA has encouraged observers to make scientifically valuable observations, often in collaborat ...

br>VSS light curves
{{DEFAULTSORT:W Cephei Cephei, W Cepheus (constellation) Spectroscopic binaries Emission-line stars K-type supergiants M-type supergiants B-type main-sequence stars Semiregular variable stars BD+57 2568 214369 111592