Radial Variables as Tracers of Stellar Populations

Abstract

Since Baade’s identification of two different stellar populations in the Milky Way, variable stars have been representing a fundamental tool for tracing the properties of both Pop. I and Pop. II stars. The prototypes of Pop. II and Pop. I variables are RR Lyrae and classical Cepheids respectively. As for RR Lyrae, the long term survey (more than ten year long) by Suntzeff et al. (1991) provided us with a complete mapping of the metallicity gradient fions the outer halo down to the Galactic center, finding that the nature of the metallicity of the Galactic halo changes at the solar circle. In fact, according to these authors, the average metallicity outside the solar circle is < [Fe/H] >_ §1.65 with a dispersion of 0.30 dex, whereas inside the solar circle the metallicity gradient is -0.06 dex Kpc