7 Summary

The proper motions and parallaxes of 205 open clusters were determined from 630 certain and 100 possible members found in the Hipparcos Catalogue. A comparison of the parallaxes with photometric distances from Loktin et al. (1997) argues for a decrease of the photometric distance scale by $12\% \pm 6\%$, while the distance scale of Dambis (1999) is in good agreement with Hipparcos. No evidence for unaccounted small-scale correlated errors in the Hipparcos Catalogue is found by these comparisons. It therefore seems unlikely that such errors can explain the discrepancy between the Hipparcos parallax and photometric distance estimates of the Pleiades as proposed by Narayanan & Gould (1999).

With the help of the Hipparcos proper motions, we can confirm the membership of the Cepheids U Sgr in IC 4725, S Nor in NGC 6087, DL Cas in NGC 129 and V Cen in NGC 5662 and can reject the membership of SZ Tau in NGC 1647. The improved membership information may lead to better estimates for the absolute magnitudes of Cepheids.

Acknowledgements

We are grateful to Floor van Leeuwen for calculating the correlated solutions of the astrometric parameters of the open clusters for us. We acknowledge the help of Elena Glushkova and Alexander Loktin who send us their data prior to publication. We also thank Sabine Frink and an anonymous referee for making suggestions which improved the paper. Extensive use has been made of the Simbad and BDA databases. HB is supported by the Sonderforschungsbereich 328 Entwicklung von Galaxien.