1997A&A...326..640S

Differential Stroemgren uvby photometry of ζ¹ Sco collected during the time interval 1982-1995 is analysed together with new VBLUW photometry with a complementary discussion of unpublished JHKLM data. We report the discovery of a ∼1750-2200d regular oscillation of amplitude ∼0.01mag in all bands, and pulsation-like oscillations with at least one frequency f₁=0.03155 (P∼32days) and a possible second frequency f₂∼5/4 f₁ ∼0.03891 (P∼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 the historic light curve of ζ¹ Sco which shows that two centuries ago the star was about 2 magnitudes brighter, while a millenium ago it was only 1 magnitude brighter than today, an indication that ζ¹ Sco should be regarded as a candidate Luminous Blue Variable.