Chemical Abundances of Red Giant Stars in the Globular Cluster M107 (NGC 6171)

TL;DR

This study analyzes chemical abundances in 13 red giant stars of the globular cluster M107, revealing moderate metallicity, slight star-to-star variation, and enrichment patterns in aluminum and r-process elements, using moderate-resolution spectroscopy.

Contribution

First detailed spectroscopic analysis of Al and neutron-capture elements in M107's red giants, refining cluster parameters and chemical abundance patterns.

Findings

M107 is moderately metal-poor with [Fe/H] ≈ -0.93.

Stars show consistent aluminum enhancement with [Al/Fe] ≈ +0.39.

Cluster exhibits moderate r-process enrichment with [Eu/La] ≈ +0.32.

Abstract

We present chemical abundances of Al and several Fe-Peak and neutron-capture elements for 13 red giant branch stars in the Galactic globular cluster NGC 6171 (M107). The abundances were determined using equivalent width and spectrum synthesis analyses of moderate resolution (R~15,000), moderate signal-to-noise ratio (<S/N>~80) spectra obtained with the WIYN telescope and Hydra multifiber spectrograph. A comparison between photometric and spectroscopic effective temperature estimates seems to indicate a reddening value of E(B-V)=0.46 may be more appropriate for this cluster than the more commonly used value of E(B-V)=0.33. Similarly, we found that a distance modulus of (m-M)V~13.7 provided reasonable surface gravity estimates for the stars in our sample. Our spectroscopic analysis finds M107 to be moderately metal-poor with <[Fe/H]>= -0.93 and also exhibits a small star-to-star metallicity dispersion (sigma=0.04). These results are consistent with previous photometric and spectroscopic studies. Aluminum appears to be moderately enhanced in all program stars (<[Al/Fe]>=+0.39, sigma=0.11). The relatively small star-to-star scatter in [Al/Fe] differs from the trend found in more metal-poor globular clusters, and is more similar to what is found in clusters with [Fe/H] greater than about -1. The cluster also appears to be moderately r-process enriched with <[Eu/La]>=+0.32 (sigma=0.17).