CAPOS: The bulge Cluster APOgee Survey

X. Chemical analysis of the Bulge Globular Cluster Djorg 2

¹ Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile
² Universidad Andres Bello, Facultad de Ciencias Exactas, Departamento de Física y Astronomía – Instituto de Astrofísica, Autopista Concepcion-Talcahuano 7100, Talcahuano, Chile
³ Departamento de Astronomía, Facultad de Ciencias, Universidad de La Serena, Av. Raul Bitran 1305, La Serena, Chile
⁴ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile

^★ Corresponding authors: This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 23 May 2025
Accepted: 1 December 2025

Abstract

Context. This study presents detailed elemental abundances in the intermediate-metallicity bulge globular cluster Djorg 2 based on high-resolution near-infrared spectra of six (R ~ 22 500) members obtained through the bulge Cluster APOgee Survey (CAPOS). CAPOS is focused on the study of clusters within the Galactic bulge and uses the APOGEE-2S as part of the Sloan Digital Sky Survey IV (SDSS-IV).

Aims. This study was undertaken to chemically explore this poorly studied cluster and to analyze it for the first time using the code BACCHUS, with the main objective of deriving the mean chemical abundances for a number of species and investigating the occurrence of multiple populations.

Methods. We employed BACCHUS to provide the line-by-line elemental abundances of a variety of species, including α-elements (O, Mg, Si, Ca, and Ti), light elements (C and N), the odd-Z element Al, the s-process element (Ce), and iron-peak elements (Fe and Ni).

Results. We found an average metallicity of [Fe/H] = –1.04 ± 0.06, without an indication of an intrinsic spread. The mean values for the other elements and their standard deviations are [C/Fe] = –0.35 ± 0.18, [N/Fe] = 0.38 ± 0.40, [O/Fe] = 0.22 ± 0.18, [Mg/Fe] = 0.38 ± 0.05, [Al/Fe] = 0.32 ±0.15, [Ca/Fe] = 0.21 ± 0.10, [Si/Fe] = 0.38 ± 0.05, [Ce/Fe] = +0.00 ± 0.06, [Ti/Fe] = +0.12 ± 0.08 and [Ni/Fe] = +0.09 ± 0.06.

Conclusions. The typical α-element enrichment in Djorg2 follows the trend of other metal-rich globular clusters. We found evidence for intrinsic spreads in C, N and O, which furthermore show the C:N and N:O anticorrelations that are typical of globular clusters. Ce shows no intrinsic variation, and in particular no correlation with N or Al. We found that Djorg 2 moves in a very elongated and flat orbit, that always remains inside the bulge and does not move far away in altitude above the Galactic plane. Moreover, it moves in a retrograde direction (backward to the rotation of the galaxy) and is not trapped by the galactic bar.