Detection of the evolutionary stages of variables in M3

J. Jurcsik, J. M. Benko, G. Á Bakos, B. Szeidl, R. Szabó

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The large number of variables in M3 provides a unique opportunity to study an extensive sample of variables with the same apparent distance modulus. Recent, high-accuracy CCD time series of the variables show that according to their mean magnitudes and light-curve shapes, the variables belong to four separate groups. Comparing the properties of these groups (magnitudes and periods) with horizontal-branch evolutionary models, we conclude that these samples can be unambiguously identified with different stages of the horizontal-branch stellar evolution. Stars close to the zero-age horizontal branch show Oosterhoff I (Oo I) type properties, while the brightest stars have Oo II type statistics regarding their mean periods and RRab/RRc number ratios. This finding strengthens the earlier suggestion of Lee, Demarque, & Zinn, connecting the Oo dichotomy to evolutionary effects; however, it is unexpected to find large samples of both of the Oo types within a single cluster, which is, moreover, the prototype of the Oo I class globular clusters. The very slight difference between the Fourier parameters of the stars (at a given period) in the three fainter samples spanning over about 0.15 mag range in Mv points to the limitations of any empirical methods that aim to determine accurate absolute magnitudes of RR Lyrae stars solely from the Fourier parameters of the light curves.

Original languageEnglish (US)
Pages (from-to)L49-L52
JournalAstrophysical Journal
Issue number1 II
StatePublished - Nov 1 2003
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Globular clusters: individual (M3)
  • Stars: Population II
  • Stars: evolution
  • Stars: horizontal-branch
  • Stars: variables: other


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