The Chemical Composition of Red Giant Branch Stars in the Galactic Globular Clusters NGC 6342 and NGC 6366

TL;DR

This study analyzes the chemical compositions and radial velocities of red giant stars in two Galactic bulge globular clusters, NGC 6342 and NGC 6366, revealing their metallicities, element abundance patterns, and potential O-Na anti-correlations.

Contribution

It provides high-resolution spectroscopic data on these clusters, highlighting their chemical similarities and differences with other inner Galaxy clusters and field stars.

Findings

Both clusters have similar metallicities (~ -0.55)

NGC 6366 shows evidence of O-Na anti-correlation

Clusters have larger [Na/Fe] spreads and enhanced [La/Fe] ratios

Abstract

We present radial velocities and chemical abundances for red giant branch stars in the Galactic bulge globular clusters NGC 6342 and NGC 6366. The velocities and abundances are based on measurements of high resolution (R > 20,000) spectra obtained with the MMT-Hectochelle and WIYN-Hydra spectrographs. We find that NGC 6342 has a heliocentric radial velocity of +112.5 km/s (sigma = 8.6 km/s), NGC 6366 has a heliocentric radial velocity of -122.3 km/s (sigma = 1.5 km/s), and that both clusters have nearly identical metallicities ([Fe/H] ~ -0.55). NGC 6366 shows evidence of a moderately extended O-Na anti-correlation, but more data are needed for NGC 6342 to determine if this cluster also exhibits the typical O-Na relation likely found in all other Galactic globular clusters. The two clusters are distinguished from similar metallicity field stars as having larger [Na/Fe] spreads and enhanced [La/Fe] ratios, but we find that NGC 6342 and NGC 6366 display alpha and Fe-peak element abundance patterns that are typical of other metal-rich ([Fe/H] > -1) inner Galaxy clusters. However, the median [La/Fe] abundance may vary from cluster-to-cluster.