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We present our detailed spectroscopic analysis of the chemical composition offour red giant stars in the halo globular cluster NGC 6426. We obtainedhigh-resolution spectra using the Magellan2/MIKE spectrograph, from which wederived equivalent widths and subsequently computed abundances of 24 species of22 chemical elements. For the purpose of measuring equivalent widths, wedeveloped a new semi-automated tool, called EWCODE. We report a mean Fe contentof [Fe/H] = -2.34$\pm$0.05 dex (stat.) in accordance with previous studies. Ata mean $\alpha$-abundance of [(Mg,Si,Ca)/3 Fe] = 0.39$\pm$0.03 dex, NGC 6426falls on the trend drawn by the Milky Way halo and other globular clusters atcomparably low metallicities. The distribution of the lighter $\alpha$-elementsas well as the enhanced ratio [Zn/Fe] = 0.39 dex could originate from hypernovaenrichment of the pre-cluster medium. We find tentative evidence for a spreadin the elements Mg, Si, and Zn, indicating an enrichment scenario, where ejectaof evolved massive stars of a slightly older population polluted a newly bornyounger one. The heavy element abundances in this cluster fit well into thepicture of metal-poor globular clusters, which in that respect appear to beremarkably homogeneous. The pattern of the neutron-capture elements heavierthan Zn point towards an enrichment history governed by the r-process with onlylittle -if any- sign of s-process contributions. This finding is supported bythe striking similarity of our program stars to the metal-poor field star HD108317.

Insights into the chemical composition of the metal-poor Milky Way halo globular cluster NGC 6426