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), serving as an example, shows brightness fluctuations between magnitudes +1.21 and +1.29. Small amplitude rapid variations have been observed in 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.