Variability type ACYG (from B/gcvs/vartype.txt)

ACYG   Variables of the Alpha Cygni type, which are nonradially pulsating
       supergiants of Bep-AepIa spectral types. The light changes with
       amplitudes of the order of 0.1 mag often seem irregular, being
       caused by the superposition of many oscillations with close
       periods. Cycles from several days to several weeks are observed.