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In page Luminous blue variable:

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Variable star types are usually named after the first member discovered to be variable, for example δ Sct variables named after the star δ Sct. The first luminous blue variable to be identified as a variable star was P Cygni, and these stars have been referred to as P Cygni type variables. The General Catalogue of Variable Stars decided there was a possibility of confusion with P Cygni profiles, which also occur in other types of stars, and chose the acronym SDOR for "variables of the S Doradus type".[5] The term "S Doradus variable" was used to describe P Cygni, S Doradus, η Carinae, and the Hubble-Sandage variables as a group in 1974.[6]