On the metallicity of open clusters II. Spectroscopy
  In a series of three papers, we investigate the current status of published
metallicities for open clusters that were derived from a variety of photometric
and spectroscopic methods. The current article focuses on spectroscopic
methods. The aim is to compile a comprehensive set of clusters with the most
reliable metallicities from high-resolution spectroscopic studies. This set of
metallicities will be the basis for a calibration of metallicities from
different methods. The literature was searched for [Fe/H] estimates of
individual member stars of open clusters based on the analysis of
high-resolution spectra. For comparison, we also compiled [Fe/H] estimates
based on spectra with low and intermediate resolution. At medium and high
resolution, we found that differences in the analysis methods have a stronger
effect on metallicity than quality differences in the observations. We retained
only highly probable cluster members and introduced a restriction on
atmospheric parameters. We combined 641 individual metallicity values for 458
stars in 78 open clusters from 86 publications to form our final set of
high-quality cluster metallicities. The photometric metallicities discussed in
the first paper of this series are systematically lower than the spectroscopic
ones by about 0.1 dex, and the differences show a scatter of about 0.2 dex. In
a preliminary comparison of our spectroscopic sample with models of Galactic
chemical evolution, none of the models predicts the observed radial metallicity
gradient. Photometric metallicities show a large intrinsic dispersion, while
the more accurate spectroscopic sample presented in this paper comprises fewer
than half the number of clusters. Only a sophisticated combination of all
available photometric and spectroscopic data will allow us to trace the
metallicity distribution in the Galactic disk on a local and global scale.
