CYCLICITIES IN THE LIGHT VARIATIONS OF LBVS .1. THE MULTI-PERIODIC BEHAVIOR OF THE LBV CANDIDATE ZETA(1) SCO

Differential Stromgren uvby photometry of zeta' Sco collected during t he time interval 1982-1995 is analysed together with new VBLUW photome try with a complementary discussion of unpublished JHKLM data. We repo rt the discovery of a similar to 1750-2200 d regular oscillation of am plitude similar to 0.(m)01 in all bands, and pulsation-like oscillatio ns with at least one frequency f(1) = 0.03155 (P similar to 32 days) a nd a possible second frequency f(2) similar to 5/4f(1) similar to 0.03 891(P similar to 25.7 days). Most likely, all such stars exhibit multi -periodic light variability. A strong noise component remaining in the prewhitened signal leads us to postulate that the driver for LBV-like eruptions is stochastic resonance. This hypothesis is supported by th e historic light curve of zeta' Sco which shows that two centuries ago the star was about 2 magnitudes brighter, while a millenium ago it wa s only 1 magnitude brighter than today, an indication that zeta' Sco s hould be regarded as a candidate Luminous Blue Variable.