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High-resolution CCD spectra of stars in globular clusters. IV - Carbon isotope ratios in red giants
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1989
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Cosmic AbundancePhotometryHigh-resolution Ccd SpectraCarbon Isotope RatiosStellar StructureAstrochemistryAstrophysical SimulationIsotope RatiosRed GiantsBarium StarAstrophysics
Carbon isotope ratios for stars in four globular clusters are derived by means of spectrum synthesis analysis of CN features in high-resolution spectra around 8000 A. In the strong-CN stars in the clusters M4, M22, Omega Cen, and 47 Tuc, the isotope ratios are generally quite low, approaching the equilibrium value in the CN cycle, namely 3-8; this includes a barium star and an S star in Omega Cen and a CH star in M22. (C-13)N is not detected in weak-CN stars, but the limits on the (C-12)/(C-13) ratios in these stars are not significant. Ratios as low as 3-8 are not predicted by standard evolution models of low-mass metal-poor stars.