Light variations of massive stars ( α Cyg variables ) ?

Multi-colour photometry of four variable supergiants in the LMC and SMC, viz. R 85, R 110, R 42 and R 45, is searched for periods, studied and discussed. The suspected LBV R 85 is undoubtedly an active LBV, though not as spectacular as R 110. Their microvariations superimposed on the S Dor-activity are analyzed as well as those exhibited by R 42 and R 45. Often, a period search is difficult because of the very complicated micro-variability. We suggest that this is caused by an intricate multi-cyclic behaviour combined with stochastic processes. The length of the strongest cyclicity in the power spectrum of R 42 (128 d) is of the order of the rotation periods of BA-type supergiants. In connection with our findings described in the present paper and the previous ones, we discuss various competing theoretical models on the instability of α Cyg variables, including the LBVs.