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The Oosterhoff period groups and the age of globular clusters. I Photometry of cluster variables in M15
Sandage, A.; Katem, B.; Sandage, M.
AA(Mount Wilson and Las Campanas Observatoires, Pasadena, CA), AB(Mount Wilson and Las Campanas Observatoires, Pasadena, CA), AC(Mount Wilson and Las Campanas Observatoires, Pasadena, CA)
Astrophysical Journal Supplement Series, vol. 46, May 1981, p. 41-74. (ApJS Homepage)
Publication Date:
NASA/STI Keywords:
Abundance, Globular Clusters, Stellar Evolution, Stellar Spectrophotometry, Variable Stars, Color, Helium, Horizontal Branch Stars, Light Curve, Main Sequence Stars, Metallic Stars, Stellar Luminosity, Tables (Data)
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Three-color photometry is used to study distributions of color, amplitudes, light-curve shapes, and periods within the instability strip of 60 RR Lyrae stars in M15. Period-amplitude, period-rise time, period-color, and color-amplitude relations are compared with data for M3, and correlations of parameters involving period are shifted by delta log P = 0.055 to longer periods in M15. An M15 horizontal branch brighter than that in M3 by delta log L(HB) = 0.090 is found to be the only explanation consistent with the Ritter condition. The abundance is shown to differ between the clusters by delta Y(M15 minus M3) = +0.05 + or - 0.02 using zero-age horizontal branch models, and the ages of M3 and M15 are shown the same within 0.5 sigma of the combined error. The mean age is found using Iben-Rood and Yale models, and HB luminosity and metallicity is found to be the same as required for main-sequence turnoff luminosity for two clusters of same age and different metallicities.

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