1. Heidelberg Institute for Theoretical Studies, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg, Germany
2. Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12–14, D-69120 Heidelberg, Germany
3. Department of Physics and Astronomy, Stocker Road, University of Exeter, Exeter EX4 4QL, UK
4. Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany
5. TIFR Center for Applicable Mathematics, Bangalore 560065, India
6. Department of Mathematics, Universität Würzburg, Emil Fischer Str. 40, D-97074 Würzburg, Germany