The prototype of these stars, Deneb (α Cygni), exhibits fluctuations in brightness between magnitudes +1.21 and +1.29. Small amplitude rapid variations have been known in many early supergiant stars, but they were not formally grouped into a class until the 4th edition of the General Catalogue of Variable Stars was published in 1985.
Deneb (α Cygni), which serves as the prototype for these stars, displays brightness fluctuations ranging from +1.21 to +1.29. Small amplitude rapid variations have been observed in many early supergiant stars but were not formally classified into a group until the 4th edition of the General Catalogue of Variable Stars was published in 1985.