Metal‐rich RR Lyrae Variables. II. The Pulsational Scenario

We present a theoretical investigation on the pulsational behavior ofmetal-rich RR Lyrae variables over the range of evolutionary parameterssuitable for stars with metallicities Z= 0.006, 0.01 and 0.02. With theaddition of similar results for metal-poor pulsators we discuss the theoreticalpulsational scenario covering the metallicity range from Z=0.0001 to 0.02. Wefind that the distribution of field ab-type RR Lyrae stars in theperiod-metallicity plane can be easily understood within the framework of thepresent theoretical scenario, suggesting that the Oosterhoff dichotomy alsoaffects field variables. Theoretical predictions concerning theamplitude-period diagram are discussed and compared with observational data. Wefind a general agreement for metal-poor ([Fe/H]<-1.4) RR Lyrae stars, whereasmore metal-rich variables show amplitudes smaller than those predicted forpulsators originated from old, low-mass evolving stars. Alternatively, theagreement between theory and observations would require that a substantialfraction of metal-rich RR Lyrae variables in the Galactic field were youngerthan approximately 2 Gyr. The comparison between the pulsational behavior of RRLyrae either in the Galactic field or in the Galactic bulge discloses theevidence that, at least as far as RR Lyrae variables are concerned, themetal-rich components of the bulge and of the field population appear quitesimilar.Comment: 21 pages, 19 ps figures, 5 ps tables, uses aaspp4.sty and tighten.sty, accepted for publication in Ap