An Rr Lyrae Period Shift in Terms of the Fourier Parameter Ïł31
نویسندگان
چکیده
The Fourier phase parameter ¢31 has been determined for RRc stars in five globular clusters NGC 6171 !"I 5, M.3, M?3, an~ M15. The results. indicate that the RRc. s!ars in a.given cluster show a seq~ence of ¢3: In~reasIn~ wIth penod, and that the hIgher !he cluster metalhclty, the higher the sequence lies in a plot of ¢31 wIth penod. The ¢31 values for the stars In NGC 6171 and M5 presented here are based on observations made with the Universit!' of Toronto 0.61 m telescope at Las Campanas, Chile, while those fqr M3, M53, and M15 are based on published data. A bootstrap procedure has been used to establish the uncertainties in the Fourier paramet~rs. The physical significance of the relationship among ¢31' period, and metallicity is not yet understood. It wIll need to be tested with hydrodynamic pulsation models computed with new opacities. Subject headings: globular clusters: general stars: oscillation stars: variables: others .
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