Chemical abundances in the metal-intermediate GC NGC 6723

Abstract

We have performed a detailed spectral analysis of the inner halo Galactic globular cluster (GC) NGC 6723 using high-resolution (R ≈ 22 000–48 000) spectra for for 11 red giant branch stars collected with MIKE (Magellan) and FEROS (MPG/ESO). This globular is located at the minimum of the bimodal metallicity distribution of GCs, which suggests that it might be an excellent transitional system between metal-intermediate and metal-rich GCs. In spite of its metal-intermediate status, it is characterized by an extended horizontal branch and by a large number of RR Lyrae stars. We investigated abundances of a variety of species, including light, α-, Fe-peak, and neutron-capture elements. We found a mean metallicity [Fe/H] = −0.93 ± 0.05 dex and typical α-enrichment ([α/Fe] ≈ 0.39) that follows the trend of metal-poor and metal-intermediate GCs. The same outcome applies for light metals (Na, Al), Fe-peak (V, Cr, Mn, Fe, Co, Ni, Cu) and s/r-process elements (Ba, Eu), and for the classical anticorrelation: Na–O and Mg–Al. The current findings further support the evidence that the chemical enrichment of NGC 6723 is more in line with metal-intermediate GCs and their lower metallicity counterparts, and it does not bring forward the prodrome of the metal-rich regime.