METALLICITY EFFECTS ON RR LYRAE VARIABLES

Since the seminal paper of Preston, the existence of a metal-rich comp onent among the RR Lyrae variable stars belonging to the solar neighbo rhood has become a well-known observational fact. In this investigatio n the effects of heavy-element abundance on theoretical observables is studied for both fundamental and first-overtonepulsators at fixed mas s (M/M.=0.53) and luminosity level [log (L/L.)=1.51]. In order to cove r the observed range of RR Lyrae metallicity, the nonlinear models hav e 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 f irst-overtone pulsators decreases as the metallicity increases, wherea s for fundamental pulsators the amplitude is positively correlated wit h the metal abundance.