Metallicities and distances of galactic clusters as determined from UBV-data. III. Ages and abundance gradients of open clusters.
The metallicities and distances of 38 open clusters are used to estimate the variation of metal abundance along the galactic disc. The resulting gradient amounts to d[Fe/H]/dR = -0.11 ± 0.02 kpc-1. No abundance gradient perpendicular to the galactic plane can be detected using open clusters with z<800pc. The ages of the clusters are determined using the turn-off point method in the H-R diagram. They cover a span of 5.1 billion years. It is shown that young clusters are placed in the galactic plane whereas the older clusters preferentially lie at higher z-values. No firm relationship between the cluster ages and their metallicity can be deduced; rather, it can be shown that at a given age there seems to be a spread in metallicity of up to ±0.3 dex. Finally, it is argued that the overall cluster-metallicity ought to be deduced from mainsequence stars rather than from giants.
Astronomy and Astrophysics
- Pub Date:
- June 1985