O and Na abundance patterns in open clusters of the Galactic disk

Abstract

Aims. A global O-Na abundance anti-correlation is observed in globular clusters, which is not present in the Galactic field population. Open clusters are thought to be chemically homogeneous internally. We aim to explore the O and Na abundance pattern among the open cluster population of the Galactic disk.

Methods. We combine open cluster abundance ratios of O and Na from high-resolution spectroscopic studies in the literature and normalize them to a common solar scale. We compare the open cluster abundances against the globular clusters and disk field.

Results. We find that the different environments show different abundance patterns. The open clusters do not show the O-Na anti-correlation at the extreme O-depletion/Na-enhancement as observed in globular clusters. Furthermore, the high Na abundances in open clusters do not match the disk field stars. If real, it may be suggesting that the dissolution of present-day open clusters is not a significant contribution to building the Galactic disk. Large-scale homogeneous studies of clusters and field will further confirm the reality of the Na enhancement.