Light variations of massive stars (alpha Cyg variables). XVI. The LMC supergiants R 85 (LBV) and R 110 (LBV) and the SMC supergiants R 42 and R 45

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 alpha Cyg variables, including the LBVs. Based on observations obtained at the European Southern Observatory at La Silla, Chile (observing proposals 55D-0317, 56D-0249, 57D-0133 and 58D-0118)