Properties of variable mean mag OGLE RR Lyrae

Hitherto this phenomenon was not studied, as it was generally assumed to be related to problems with the photometry. We investigate whether the mean magnitude variability of RR Lyrae variables is due to genuine astrophysical phenomena.

We make use of the extended, and in many cases overlapping, light curves from multiple microlensing surveys, to study RR Lyrae stars with apparent mean-magnitude variations. A modified Fourier-series based fitting method is introduced to analyze the light curves showing mean-magnitude variations. Data from infrared surveys are also used to construct spectral energy distributions (SEDs). 72 stars are presented where the mean-magnitude variations are most probably of genuine astrophysical origin, and not the result of problems with the photometry.