AN RR LYRAE PERIOD SHIFT IN TERMS OF THE FOURIER PARAMETER PHI-31

The Fourier phase parameter phi-31 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 phi-31 increasing with period, and that the higher the cluster metallicity, the higher the sequence lies in a Plot Of phi-31 with period. The phi-31 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 phi-31, period, and metallicity is not yet understood. It will need to be tested with hydrodynamic pulsation models computed with new opacities.