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High-resolution near-infrared spectra of NGC 6624 and 6569


  • Data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The observatory was made possible for studies by the generous support of the W. M. Keck Foundation.



We present the first abundance analysis based on high-resolution infrared (IR) echelle spectra of NGC 6569 and 6624, two moderately reddened globular clusters located in the outer bulge of the Galaxy.

We find [Fe/H]=−0.79 ± 0.02 and −0.69 ± 0.02 dex for NGC 6569 and 6624, respectively, and an average α-element enhancement of ≈+0.43 ± 0.02 and +0.39 ± 0.02 dex, consistent with previous measurements on other metal-rich bulge clusters. We measure accurate radial velocities of vr〉=−47 ± 4 and +51 ± 3 km s−1 and velocity dispersions of ≈8 and 6 km s−1 for NGC 6569 and 6624, respectively.

Finally, we find very low 12C/13C isotopic ratio (≤7 in NGC 6624 and ≈5 in NGC 6569), confirming the presence of extramixing mechanisms during the red giant branch evolution phase.

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