Globular Cluster Intrinsic Iron Abundance Spreads: I. Catalog

TL;DR

This paper compiles a detailed catalog of iron abundance variations within 55 Milky Way globular clusters, revealing small but significant spreads that correlate with cluster luminosity.

Contribution

It provides the first comprehensive catalog of intrinsic iron spreads in globular clusters, using high-resolution spectroscopy and combining multiple datasets for improved accuracy.

Findings

Median iron spread is 0.045 dex, non-zero in most clusters.

More luminous clusters tend to have larger iron spreads.

No correlation between iron spread and overall metallicity.

Abstract

We present an up-to-date catalog of intrinsic iron abundance spreads in the 55 Milky Way globular clusters for which sufficiently precise spectroscopic measurements are available. Our method combines multiple datasets when possible to improve the statistics, taking into account the fact that different methods and instruments can lead to systematically offset metallicities. Only high spectral resolution (R>14,000) studies that measure the equivalent widths of individual iron lines are found to have uncertainties on the metallicities of the individual stars that can be calibrated sufficiently well for the intrinsic dispersion to be separated cleanly from random measurement error. The median intrinsic iron spread is found to be 0.045 dex, which is small but unambiguously measured to be non-zero in most cases. There is large variation between clusters, but more luminous globular clusters, above 10^5 L_sun, have increasingly large iron spreads on average; no trend between iron spread and metallicity is found.