Metallicity in the Galactic Center: The Quintuplet cluster

TL;DR

This study measures the metallicity of the Quintuplet Cluster in the Galactic center using spectral analysis of LBVs, revealing solar iron levels and enhanced alpha-elements, which inform Galactic chemical evolution.

Contribution

It provides the first robust metallicity estimates for LBVs in the Galactic center using high-resolution near-infrared spectra and advanced NLTE wind/atmosphere models.

Findings

Solar iron abundance in the Quintuplet Cluster

Alpha-elements are roughly twice as abundant as in the Sun

Results support a history of extensive nucleosynthesis in high-mass stars

Abstract

We present a measurement of metallicity in the Galactic center Quintuplet Cluster made using quantitative spectral analysis of two Luminous Blue Variables (LBVs). The analysis employs line-blanketed NLTE wind/atmosphere models fit to high-resolution near-infrared spectra containing lines of H, HeI, SiII, MgII, and FeII. We are able to break the H/He ratio vs. mass-loss rate degeneracy found in other LBVs and to obtain robust estimates of the He content of both objects. Our results indicate solar iron abundance and roughly twice solar abundance in the alpha-elements. These results are discussed within the framework of recent measurements of oxygen and carbon composition in the nearby Arches Cluster and iron abundances in red giants and supergiants within the central 30 pc of the Galaxy. The relatively large enrichment of alpha-elements with respect to iron is consistent with a history of more nucleosynthesis in high mass stars than the Galactic disk.