CAPOS: The bulge Cluster APOgee Survey

III. Spectroscopic tomography of Tonantzintla 2

¹ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
e-mail: jose.fernandez@ucn.cl; jfernandezt87@gmail.com
² Departamento de Astronomía, Casilla 160-C, Universidad de Concepción, Concepción, Chile
³ Department of Astronomy – Universidad de La Serena, Av. Juan Cisternas, 1200, North, La Serena, Chile
⁴ Instituto de Investigación Multidisciplinario en Ciencia y Tecnología, Universidad de La Serena, Benavente 980, La Serena, Chile
⁵ Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
⁶ Depto. de Cs. Físicas, Facultad de Ciencias Exactas, Universidad Andrés Bello, Av. Fernández Concha 700, Las Condes, Santiago, Chile
⁷ Vatican Observatory, V00120 Vatican City State, Italy
⁸ Department of Physics and JINA Center for the Evolution of the Elements, University of Notre Dame, Notre Dame, IN 46556, USA
⁹ ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, Szent Imre H. st. 112, 9700 Szombathely, Hungary
¹⁰ MTA-ELTE Exoplanet Research Group, Szombathely, Hungary
¹¹ MTA-ELTE Lendület Milky Way Research Group, Szombathely, Hungary
¹² School of Physics and Astronomy, Sun Yat-sen University, Zhuhai 519082, PR China
¹³ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA

Received: 8 July 2021
Accepted: 19 October 2021

Abstract

We performed the first detailed spectral analysis of red giant members of the relatively high-metallicity globular cluster (GC) Tononzintla 2 (Ton 2) using high-resolution near-infrared spectra collected with the Apache Point Observatory Galactic Evolution Experiment II survey (APOGEE-2), obtained as part of the bulge Cluster APOgee Survey. We investigated chemical abundances for a variety of species including the light, odd-Z, α-, Fe-peak, and neutron-capture elements from high S/N spectra of seven giant members. The derived mean cluster metallicity is [Fe/H] = −0.70 ± 0.05, with no evidence for an intrinsic metallicity spread. Ton 2 exhibits a typical α-enrichment that follows the trend for high-metallicity Galactic GCs, similar to that seen in 47 Tucanae and NGC 6380. We find a significant nitrogen spread (> 0.87 dex), and a large fraction of nitrogen-enriched stars that populate the cluster. Given the relatively high-metallicity of Ton 2, these nitrogen-enriched stars are well above the typical Galactic levels, indicating the prevalence of the multiple-population phenomenon in this cluster that also contains several stars with typical low first-generation N abundances. We also identify the presence of [Ce/Fe] abundance spread in Ton 2, which is correlated with the nitrogen enhancement, indicating that the s-process enrichment in this cluster has likely been produced by relatively low-mass asymptotic giant branch stars. Furthermore, we find a mean radial velocity of the cluster, −178.6 ± 0.86 km s⁻¹, with a small velocity dispersion, 2.99 ± 0.61 km s⁻¹, which is typical of GCs. We also find a prograde bulge-like orbit for Ton 2 that appears to be radial and highly eccentric. Finally, the considerably nitrogen-enhanced population observed in Ton 2, combined with its dynamical properties, makes this object a potential progenitor for the nitrogen-enriched field stars identified so far toward the bulge region at similar metallicity.