CAPOS: The bulge Cluster APOgee Survey VII. First detailed chemical analysis of NGC 6316

TL;DR

This study provides the first detailed chemical analysis of NGC 6316, revealing its true metallicity, chemical abundance patterns, and clarifying its classification within the bulge globular clusters.

Contribution

It offers the first comprehensive chemical abundance measurements for NGC 6316, revising its metallicity and cluster membership status with high-resolution spectroscopy.

Findings

Mean metallicity [Fe/H] = -0.87 with no intrinsic spread

Detected a clear C-N anticorrelation

Measured [α/Fe] = 0.31

Abstract

As part of the bulge Cluster APOgee Survey (CAPOS), high-resolution, high Signal-to-Noise Ratio Near-Infrared spectroscopy, we aim to conduct the most robust chemical study to date for NGC 6316, deriving abundances for a number of elements with a variety of nucleosynthetic origins, most of which have never been studied before in this cluster. We use the Brussels Automatic Code for Characterizing High accuracy Spectra (BACCHUS) with atmospheric parameters photometrically obtained in order to determine, for the first time, abundances for C, N, O, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Mn, Fe, Ni and Ce for this cluster. We obtained a mean metallicity $[Fe/H]=-0.87\pm0.02$, finding no indication of an intrinsic metallicity spread. Our metallicity agrees with the most recent values from other studies, revising earlier values that were $\sim0.5$ dex metal-richer. With this new value, this cluster, long believed to be a member of the classical metal-rich group of bulge GCs around $-0.5$, now falls in the dominant bulge globular cluster peak around $[Fe/H]=-1$. The cluster presents a clear C-N anticorrelation. We also found a $[\alpha/Fe]=0.31\pm0.02$. Our abundances show similar behaviour to other in situ globular clusters with comparable metallicity. An isochrone fitting gave us $E(B-V)=0.71$, a higher value than any other from the literature for this cluster since we also estimated $R_V=2.7$, in good agreement with determinations from other works; $(M-m)_0=15.32\pm0.05$. We derive an overall metallicity $[M/H]=-0.6\pm0.05$, in agreement with our abundance determination.