W Cephei

W Cephei is a spectroscopic binary and variable star located in the constellation Cepheus. It is thought to be a member of the Cep OB1 stellar association at about 8,000 light years. The supergiant primary star, known as W Cephei A, is one of largest known stars and as well as one of most luminous red supergiants.
Discovery.
W Cephei was reported in 1896 as a red star varying from magnitude 7.3 to 8.3. It was catalogued as BD+57°2568 in the Bonner Durchmusterung published in 1903, and HD 214369 in the Henry Draper Catalogue.
In 1925, W Cep was included in a listing of Be stars. 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 star with a non-supergiant early B companion. The star has unusual emission lines including both permitted and forbidden FeII, produced by a circumstellar envelope containing dust and ionised gas. The two components have been resolved at 0.262" using Speckle interferometry. 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 lists it as a semiregular variable but attempts to find a period have shown only random variations.