1998A&A...337..393V

Multi-colour photometry of four variable supergiants in the LMC and SMC, viz. R85, R110, R42 and R45, is searched for periods, studied and discussed. The suspected LBV R85 is undoubtedly an active LBV, though not as spectacular as R110. Their microvariations superimposed on the S Dor-activity are analyzed as well as those exhibited by R42 and R45. 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 R42 (128d) 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.