H-band discovery of additional Second-Generation stars in the Galactic Bulge Globular Cluster NGC 6522 as observed by APOGEE and Gaia

TL;DR

This study identifies second-generation stars in the NGC 6522 globular cluster using H-band spectra from APOGEE, revealing chemical patterns consistent with multiple stellar populations and challenging previous enrichment hypotheses.

Contribution

First H-band spectroscopic confirmation of second-generation stars in NGC 6522, demonstrating multiple stellar populations with specific chemical signatures.

Findings

Confirmed two new second-generation stars with typical SG abundance patterns.

Observed only mild Ce overabundance, suggesting AGB stars as primary polluters.

Supported presence of multiple stellar generations in NGC 6522.

Abstract

We present elemental abundance analysis of high-resolution spectra for five giant stars, deriving Fe, Mg, Al, C, N, O, Si and Ce abundances, and spatially located within the innermost regions of the bulge globular cluster NGC 6522, based on H-band spectra taken with the multi-object APOGEE-north spectrograph from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. Of the five cluster candidates, two previously unremarked stars are confirmed to have second-generation (SG) abundance patterns, with the basic pattern of depletion in C and Mg simultaneous with enrichment in N and Al as seen in other SG globular cluster populations at similar metallicity. } In agreement with the most recent optical studies, the NGC 6522 stars analyzed exhibit (when available) only mild overabundances of the s-process element Ce, contradicting the idea of the NGC 6522 stars being formed from gas enriched by spinstars and indicating that other stellar sources such as massive AGB stars could be the primary intra-cluster medium polluters. The peculiar abundance signature of SG stars have been observed in our data, confirming the presence of multiple generations of stars in NGC 6522.