Correlated cyanogen and sodium anomalies in the globular clusters 47 TUC and NGC 6752

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Abstract

Spectroscopic analyses have been made of echelle plates of pairs of CN-strong and CN-weak giants in the globular clusters 47 Tuc and NGC 6752. Differential analysis reveals that in NGC 6752 sodium and aluminum are enhanced in the CN-strong stars by approximately 0.5 dex and 0.2 dex, respectively. All other elements studied (Mg, Si, Ca, Fe, and Ba) appear to have identical abundances in the two groups of stars. In 47 Tuc, only sodium shows any enhancement (by about 0.4 dex) in the CN-strong stars. Since sodium and aluminum are not produced during the evolution of low-mass stars, these abundance enhancements in the CN-strong stars cannot be due to mixing. They must be primordial in origin and indicate that each protocluster gas cloud was not homogeneous during the epoch of low-mass star formation. A process by which both the sodium and cyanogen anomalies might be produced is described.

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