Letter to the Editor

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

¹ European Southern Observatory, Karl-Schwarzschild-Str 2, 85748 Garching, Germany e-mail: gdesilva@eso.org
² Jeremiah Horrocks Institute for Astrophysics & Supercomputing, University of Central Lancashire, Preston, PR1 2HE, UK
³ Centre for Stellar and Planetary Astrophysics, Monash University, Victoria 3800, Australia
⁴ Max Planck Institute für Astrophysik, Postfach 1317, 85741 Garching, Germany

Received: 5 April 2009
Accepted: 7 May 2009

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.