Metallicity effects on RR Lyrae variables

Since the seminal paper of Preston, the existence of a metal-rich component among the RR Lyrae variable stars belonging to the solar neighborhood has become a well-known observational fact. In this investigation the effects of heavy-element abundance on theoretical observables is studied for both fundamental and first-overtonepulsators at fixed mass (M/M.=0.53) and luminosity level [log (L/L.)=1.51]. In order to cover the observed range of RR Lyrae metallicity, the nonlinear models have been computed by adopting three different metal contents (Z=0.0001, 0.001, and 0.02). It has been found that the bolometric amplitude of first-overtone pulsators decreases as the metallicity increases, whereas for fundamental pulsators the amplitude is positively correlated with the metal abundance.