CAPOS: The bulge Cluster APOgee Survey

VIII. Final ASPCAP results for all clusters

¹ Departamento de Astronomía, Casilla 160-C, Universidad de Concepción, Concepción, Chile
² Departamento de Astronomía, Facultad de Ciencias, Universidad de La Serena. Av. Raul Bitran 1305, La Serena, Chile
³ Universidad Andres Bello, Facultad de Ciencias Exactas, Departamento de Ciencias Físicas – Instituto de Astrofisica, Autopista Concepcion-Talcahuano 7100, Talcahuano, Chile
⁴ Deptartment of Physics and Astronomy, Rutgers the State University of New Jersey, 136 Frelinghuysen Road., Piscataway, NJ 08854, USA
⁵ Instituto de Astrofísica, Depto. de Física y Astronomía, Facultad de Ciencias Exactas, Universidad Andres Bello, Av. Fernandez Concha 700, Santiago, Chile
⁶ Vatican Observatory, V00120 Vatican City State, Italy
⁷ Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325, USA
⁸ Saint Martin’s University, 5000 Abbey Way SE, Lacey, WA 98503, USA
⁹ Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
¹⁰ Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065, USA
¹¹ Observatório Nacional, Rua General José Cristino, 77, 20921-400 Sao Cristóvao, Rio de Janeiro, RJ, Brazil
¹² National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
¹³ Vicerrectoría de Investigación y Postgrado, Universidad de La Serena, La Serena 170000, Chile

^★ Corresponding author: douglas.geisler@userena.cl

Received: 1 April 2025
Accepted: 12 August 2025

Abstract

Context. Bulge globular clusters (BGCs) are exceptional tracers of the formation and chemodynamical evolution of this oldest Galactic component. Until now, observational difficulties have prevented us from taking full advantage of these powerful Galactic archeological tools.

Aims. The bulge Cluster APOgee Survey (CAPOS) addresses this key topic by observing a large number of BGCs, most of which have been poorly studied until now. We aim to obtain accurate mean values for metallicity, [α/Fe], and radial velocity, as well as abundances for eleven other elements. Here, we present final parameters based on the APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) for all 18 CAPOS BGCs.

Methods. We used atmospheric parameters, abundances, and velocities from ASPCAP in DR17.

Results. First, we carried out a stringent selection of cluster members, finding a total of 303 with a spectral signal-to-noise value of S/N>70 and an additional 125 with a lower S/N. We confirmed the result of prior ASPCAP multiple population studies, namely, that stars with high [N/Fe] abundances show higher [Fe/H] than their lower [N/Fe] counterparts. Furthermore, the Mg, Ca, and global α abundances exhibit similar trends, while Si is well-behaved. The [Fe/H] value of these second-population stars was corrected to derive the mean metallicity. Mean metallicities were determined to a precision of 0.05 dex, [α/Fe] to 0.06 dex, and radial velocity to 3.4 km/s. No clusters displayed any strong evidence of internal metallicity variations, including M22. Abundances for eleven other elements using only first-population stars were calculated. Our values are shown to be in good general agreement with the literature. We developed a new chemodynamical GC classification scheme, synthesizing the results of several recent studies. We also compiled a set of up-to-date metallicities. The BGC metallicity distribution is bimodal, with peaks near [Fe/H] = −0.45, and −1.1, with the metal-poor peak displaying a strong dominance. The entire in situ sample, including disk and BGCs, displays the same bimodality, while ex situ GCs are unimodal, with a peak around −1.6. Surprisingly, we see only a small and statistically insignificant difference in the mean [Si/Fe] of in situ and ex situ GCs. The four GCs with the lowest [Si/Fe] values are all ex situ and relatively young, with three belonging to Sagittarius; no other correlations are evident.