On the metallicity of open clusters. III. Homogenised sample

TL;DR

This study compiles a large, homogenized sample of open cluster metallicities to analyze the Galactic metallicity gradient, age effects, and test current models, revealing potential evidence for radial migration and discrepancies in outer disc modeling.

Contribution

It provides the largest homogeneous open cluster metallicity dataset to date, enabling detailed analysis of Galactic chemical evolution and testing of theoretical models.

Findings

Possible increase of metallicity with age, suggesting radial migration

Good overall agreement with Galactic models, except in the outer disc

Models underestimate radial migration effects or missing mechanisms

Abstract

Open clusters are known as excellent tools for various topics in Galactic research. For example, they allow accurately tracing the chemical structure of the Galactic disc. However, the metallicity is known only for a rather low percentage of the open cluster population, and these values are based on a variety of methods and data. Therefore, a large and homogeneous sample is highly desirable. In the third part of our series we compile a large sample of homogenised open cluster metallicities using a wide variety of different sources. These data and a sample of Cepheids are used to investigate the radial metallicity gradient, age effects, and to test current models. We used photometric and spectroscopic data to derive cluster metallicities. The different sources were checked and tested for possible offsets and correlations. In total, metallicities for 172 open cluster were derived. We used the spectroscopic data of 100 objects for a study of the radial metallicity distribution and the age-metallicity relation. We found a possible increase of metallicity with age, which, if confirmed, would provide observational evidence for radial migration. Although a statistical significance is given, more studies are certainly needed to exclude selection effects, for example. The comparison of open clusters and Cepheids with recent Galactic models agrees well in general. However, the models do not reproduce the flat gradient of the open clusters in the outer disc. Thus, the effect of radial migration is either underestimated in the models, or an additional mechanism is at work. [abridged]