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The Oosterhoff period groups and the age of globular clusters. II - Properties of RR Lyrae stars in six clusters - The P-L-A relation
Sandage, A.
AA(Mount Wilson and Las Campanas Observatoires, Pasadena, CA)
Astrophysical Journal, Part 1, vol. 248, Aug. 15, 1981, p. 161-176. (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Blue Stars, Giant Stars, Globular Clusters, Light Curve, Stellar Evolution, Stellar Oscillations, Variable Stars, Abundance, Line Spectra, Lyra Constellation, Stellar Magnitude, Stellar Mass, Stellar Models, Stellar Temperature
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Data for RR Lyrae stars in six clusters are used to test the conclusion of Paper I that, at every temperature, period shifts exist between variables in one cluster relative to those in another of a different Oosterhoff group. Variables in M3, M4, M15, NGC 6171, NGC 6891, and omegaCen have the same shifts in the period-temperature as in the period-amplitude relations; no shifts occur in the temperature- amplitude relation.

The period residuals, Delta log P, determined for individual stars in M3 and in omega Cen, correlate with their observed apparent magnitudes; hence, the observed spread in LRR is real. Brighter variables than others in the same cluster have longer periods at fixed Te or A. The data are consistent with DeltaMbol = 3Delta log P expected from P <rho>1/2 = constant at fixed mass.

Combining the period deviations at fixed amplitude with the observed magnitude variations leads to a period-luminosity- amplitude relation for equal metallicity ab RR Lyrae variables of the form Mbol = Mbol(M315.52) -3(log P+0.l29AB +0.088), where Mbol(M3l5.52) is the absolute magnitude of RR Lyrae stars in M3 that have Mbol = 15.52. The coefficient of the period-amplitude term will be -4.2 rather than -3 if mass is a function of metallicity as predicted by the models.

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