Intrinsic iron abundance spreads in globular clusters

Globular clusters host multiple stellar populations, likely composed of a subset of first-generation stars that enriched the intracluster medium and gave rise to second-generation (SG) stars, each characterised by distinctive chemical patterns. These patterns typically include enhancements in elements such as N, Na, and Al, coupled with depletions in C, O, and Mg in SG stars. Traditionally, heavier elements such as those in the iron peak were considered unaffected in most clusters. However, recent studies have reported significant internal spreads in these elements, suggesting a more complex picture of chemical enrichment within globular clusters. This study seeks to derive precise and homogeneous differential iron abundances in a large sample of globular clusters. By doing so, our aim is to investigate the presence of intrinsic iron spreads within them and to assess the existence of differences in Fe between their stellar populations. We used the Python-based tool to determine both differential stellar parameters and iron abundances for 92 sibling stars -- defined by the similarities in their stellar parameters -- across 13 Galactic globular clusters. This differential approach reduces the influence of non-local thermodynamic equilibrium effects, and minimises observational errors, and systematic biases linked to stellar parameters. We performed Monte Carlo simulations to evaluate the statistical significance of the measured spreads. Q2 Most of the globular clusters in our sample do not show evidence of statistically significant iron spreads. Only a few exceptions emerge, namely NGC 1851, NGC 3201, and NGC 5634, which display a highly significant iron spread. In particular, NGC 3201 shows a particularly pronounced spread in its first-generation population, reflecting a potential inhomogeneous iron abundance in its pristine material. Finally, through statistical tests, we conclude that our data do not support the presence of a widespread iron variation in globular clusters.