The Blazhko Effect in Galactic Bulge Fundamental Mode RR Lyrae Stars

The Blazhko effect is a common feature of the fundamental mode RR Lyrae stars. The large number of these stars in the Galactic bulge observed by the Optical Gravitational Lensing Experiment (OGLE) represents a great opportunity to study the Blazhko effect in a statistical manner. We investigated modulation periods, envelope shapes, and amplitudes in connection with pulsation periods, amplitudes, and shapes of the light curves in a sample of more than 3000 modulated stars. We found no simple monotonic dependence between any two parameters. There are only systematic limits. It seems that the modulation amplitude is suppressed towards longer pulsation periods. We identified 6 morphological types of the modulation and two populations of stars with different length of the modulation periods (48 and 186 days). We found that 25 % of the stars show multiple modulation. In this brief report, we also summarize other important results.