1. Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, D-85748 Garching, Germany
2. Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, NL 9700 AV Groningen, The Netherlands
3. Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS, Delft, The Netherlands
4. University of Leiden, P.O. Box 9513, NL, 2300 RA, Leiden, The Netherlands
5. CentERdata, Tilburg University, P.O. Box 90153, 5000 LE, Tilburg, The Netherlands