1. Institute for Computational Science, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland
2. Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands
3. Centre for Astronomy Research, University of Lyon, 9 avenue Charles André, F-69230 Saint-Genis-Laval, France