CAPOS: The bulge Cluster APOgee Survey

IX. Spectroscopic analysis of the bulge globular cluster Terzan 2

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

^★ Corresponding author: jose.fernandez@ucn.cl

Received: 24 June 2025
Accepted: 28 August 2025

Abstract

We present the first detailed spectroscopic analysis of the heavily extincted bulge globular cluster Terzan 2 (Ter 2) based on high-resolution near-infrared spectra obtained as part of the CAPOS (bulge Cluster APOgee Survey) project. CAPOS focuses on surveying clusters within the Galactic bulge, using the APOGEE-2S spectrograph, part of the SDSS-IV survey, a component of the second-generation Apache Point Observatory Galactic Evolution Experiment (APOGEE-2). For the spectral analysis, we used the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) code, which provides line-by-line elemental abundances. We derived abundances for the Fe-peak (Fe, Ni), α (O, Mg, Si, Ca, Ti), light (C, N), odd-Z (Al), and s-process element (Ce) for four members of the cluster. Our analysis yields a mean metallicity of [Fe/H] = −0.84 ± 0.04, with no evidence of intrinsic variation. We detect significant abundance variation only in C and N, indicating the presence of multiple populations. Ter 2 exhibits typical α enrichment, which follows the trend of Galactic globular clusters. Additionally, our dynamical analysis reveals that Terzan 2 is a bulge globular cluster with a chaotic orbit that is influenced by the Galactic bar but not trapped by it, displaying both prograde and retrograde motions within the inner bulge region. Overall, the chemical patterns observed in Terzan 2 are in good agreement with those of other CAPOS bulge clusters of a similar metallicity.