Volume 561, January 2014
|Number of page(s)||22|
|Section||Catalogs and data|
|Published online||09 January 2014|
On the metallicity of open clusters
1 Institutionen för fysik och astronomi, Uppsala universitet, Box 516, 751 20 Uppsala, Sweden
2 Université Bordeaux 1, CNRS, Laboratoire d’Astrophysique de Bordeaux UMR 5804, BP 89, 33270 Floirac, France
3 Institut für Astrophysik der Universität Wien, Türkenschanzstrasse 17, 1180 Wien, Austria
4 Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 267/2, 611 37 Brno, Czech Republic
Received: 28 August 2013
Accepted: 20 October 2013
Context. Open clusters are an important tool for studying the chemical evolution of the Galactic disk. Metallicity estimates are available for about ten percent of the currently known open clusters. These metallicities are based on widely differing methods, however, which introduces unknown systematic effects.
Aims. 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.
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 the metallicity than that of quality differences in the observations. We retained only highly probable cluster members and introduced a restriction on atmospheric parameters.
Results. 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.
Conclusions. 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.
Key words: Galaxy: abundances / open clusters and associations: general / stars: abundances
Tables 1 and 4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/561/A93
© ESO, 2014
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