AN RR LYRAE PERIOD SHIFT IN TERMS OF THE FOURIER PARAMETER ϕ31

The Fourier phase parameter ϕ31 has been determined for RRc stars in five globular clusters NGC 6171, M5, M3, M53, and M15. The results indicate that the RRc stars in a given cluster show a sequence of ϕ31 Increasing with period, and that the higher the cluster metallicity, the higher the sequence lies in a plot of ϕ31 with period. The ϕ31 values for the stars In NGC 6171 and M5 presented here are based on observations made with the University of Toronto 0.61 m telescope at Las Campanas, Chile, while those for M3, M53, and M15 are based on published data. A bootstrap procedure has been used to establish the uncertainties in the Fourier parameters. The physical significance of the relationship among ϕ31 period, and metallicity is not yet understood. It will need to be tested with hydrodynamic pulsation models computed with new opacities