Globular Cluster Abundances from High-Resolution, Integrated-Light Spectroscopy. II. Expanding the Metallicity Range for Old Clusters and Updated Analysis Techniques

TL;DR

This study evaluates the accuracy of integrated light spectroscopy for determining globular cluster abundances across a wider metallicity range, comparing results with individual star analyses and refining techniques.

Contribution

It expands the metallicity range tested for integrated light abundance analysis and provides an updated, systematic evaluation of element abundance ratios in globular clusters.

Findings

Integrated light [Fe/H] agrees within 0.1 dex up to [Fe/H]=-0.3

Certain elements like Fe I, Ca I, Si I, Ni I, Ba II show good agreement with stellar spectra

Some elements, including Mg I and Zr I, exhibit significant discrepancies

Abstract

We present abundances of globular clusters in the Milky Way and Fornax from integrated light spectra. Our goal is to evaluate the consistency of the integrated light analysis relative to standard abundance analysis for individual stars in those same clusters. This sample includes an updated analysis of 7 clusters from our previous publications and results for 5 new clusters that expand the metallicity range over which our technique has been tested. We find that the [Fe/H] measured from integrated light spectra agrees to $\sim$0.1 dex for globular clusters with metallicities as high as [Fe/H]=$-0.3$, but the abundances measured for more metal rich clusters may be underestimated. In addition we systematically evaluate the accuracy of abundance ratios, [X/Fe], for Na I, Mg I, Al I, Si I, Ca I, Ti I, Ti II, Sc II, V I, Cr I, Mn I, Co I, Ni I, Cu I, Y II, Zr I, Ba II, La II, Nd II, and Eu II. The elements for which the integrated light analysis gives results that are most similar to analysis of individual stellar spectra are Fe I, Ca I, Si I, Ni I, and Ba II. The elements that show the greatest differences include Mg I and Zr I. Some elements show good agreement only over a limited range in metallicity. More stellar abundance data in these clusters would enable more complete evaluation of the integrated light results for other important elements.