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

TL;DR

This study provides the first high-resolution IR spectral analysis of two bulge globular clusters, determining their metallicities, alpha-element enhancements, radial velocities, and evidence of extra-mixing in stellar evolution.

Contribution

It presents novel high-resolution IR spectra-based abundance analyses for NGC 6569 and NGC 6624, expanding knowledge of their chemical compositions and stellar dynamics.

Findings

Metallicities: [Fe/H]=-0.79 and -0.69 dex.

Alpha-element enhancement: +0.43 and +0.39 dex.

Radial velocities: -47 and +51 km/s.

Abstract

We present the first abundances analysis based on high-resolution infrared (IR) echelle spectra of NGC 6569 and NGC 6624, two moderately reddened globular clusters located in the outer bulge of the Galaxy. We find [Fe/H]=-0.79$\pm$0.02 dex and [Fe/H]=-0.69$\pm$0.02 dex for NGC 6569 and NGC 6624, respectively and an average $\alpha$-elements enhancement of $\approx$+0.43$\pm$0.02 dex and +0.39$\pm$0.02 dex, consistent with previous measurements on other metal-rich Bulge clusters. We measure accurate radial velocities of $\rm <v_r>=-47\pm 4 km s^{-1}$ and $\rm <v_r>=+51\pm 3 km s^{-1}$ and velocity dispersions of $\rm \approx 8 km s^{-1}$ and $\rm \approx6 km s^{-1}$ for NGC 6569 and NGC 6624, respectively. Finally, we find very low $^{12}C/^{13}C$ isotopics ratio ($\leq$7 in NGC 6624 and $\approx$5 in NGC 6569), confirming the presence extra-mixing mechanisms during the red giant branch evolution phase.