On Metallicity And RR Lyrae Light Curves

Fourier decompositions are performed for the light curves of six RRab and 3 RRc field stars. These are added to previous work to form a sample of 61 RRab and 12 RRc pulsators. The RRab stars are divided into two groups-a short-period (SP) group with P \u3c 0d.575 and a long-period (LP) group with P \u3e 0d.575. The Fourier phase parameter ϕ21 is found to fall off very regularly with decreasing metallicity among the SP stars, but this relationship disappears abruptly when one enters the LP group. A small sample of RRab stars from the globular cluster Ѡ Cen shows hints of a similar ϕ21 -metallicity relation. No trend of ϕ21 with metallicity is found for the RRc field stars. We look for a kinematic difference between the SP and LP RRab samples, but none is apparent. Finally, we use published one-zone models and new linear nonadiabatic pulsation calculations to tentatively identify the ϕ21-metallicity relation as an opacity effect. However, no explanation is found for the absence of such a relation among the long-period RRab stars