CAPOS: The bulge Cluster APOgee Survey

VII. First detailed chemical analysis of NGC 6316

¹ Universidad Andres Bello, Facultad de Ciencias Exactas, Departamento de Física y Astronomía – Instituto de Astrofísica, Autopista Concepción-Talcahuano 7100, Talcahuano, Chile
² Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
³ Departamento de Astronomía, Facultad de Ciencias, Universidad de La Serena. Av. Juan Cisternas 1200, La Serena, Chile
⁴ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile

^* Corresponding author: h.frelijjrubilar@uandresbello.edu

Received: 26 February 2025
Accepted: 22 July 2025

Abstract

Context. The bulge globular cluster (BGC) NGC 6316 has been the subject of few previous chemical studies beyond metallicity. Thanks to the bulge Cluster APOgee Survey (CAPOS), we can now improve our knowledge of the chemistry and nature of this cluster. CAPOS makes use of high-resolution, high signal-to-noise ratio near-infrared spectroscopy, which is capable of penetrating the substantial dust towards the Galactic bulge (a significant optical obstacle for this cluster due to its high reddening).

Aims. We aim to conduct the most robust chemical study to date for NGC 6316 by deriving abundances for a number of elements with a variety of nucleosynthetic origins, most of which have never been studied before in this cluster.

Methods. We used the Brussels Automatic Code for Characterizing High accuracy Spectra (BACCHUS) with atmospheric parameters photometrically obtained in order to determine the abundances

Results. We determined, for the first time, high-resolution spectroscopic 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 [Fe/H] = −0.87 ± 0.02, finding no indication of an intrinsic metallicity spread. Our metallicity agrees with the most recent values from other studies, revising earlier values that were ∼0.5 dex more metal-rich. With this new value, this cluster, long believed to be a member of the classical metal-rich group of BGCs around −0.5, now falls in the dominant BGC peak around [Fe/H] = −1. The cluster presents a clear C–N anti-correlation and [α/Fe] = 0.31 ± 0.02. 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, which is in good agreement with determinations from other works; (M–m)₀ = 15.32 ± 0.05. We derive an overall metallicity of [M/H] = −0.6 ± 0.05, which is in agreement with our abundance determination.