Metallicity dependence of the Blazhko effect

Abstract

The microlensing surveys, such as OGLE or MACHO, have led to the discovery of thousands of RR Lyrae stars in the Galactic Bulge and in the Magellanic Clouds, allowing for detailed investigation of these stars, specially the still mysterious Blazhko phenomenon. Higher incidence rate of Blazhko (BL) variables in the more metal-rich Galactic Bulge than in the LMC, suggests that occurance of Blazhko effect correlates with metallicity (Moskalik and Poretti 2003). To investigate this problem, we calibrate the photometric method of determining the metallicity of the RRab star (Kovacs and Zsoldos 1995) to the I-band and apply it to the OGLE Galactic Bulge and LMC data. In both systems, metallicities of non Blazhko and Blazhko variables are close to each other. The LMC Blazhko pulsators prefer slightly lower metallicities. The different metallicities of the Galactic Bulge and the LMC, can't explain the observed incidence rates. As a by-product of our metallicity estimates, we investigate the luminosity-metallicity relation, finding a steep dependence of the luminosity on [Fe/H]