1. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, the Netherlands
2. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA
3. GEPI, Observatoire de Paris, CNRS, Universit Paris Diderot; Place Jules Janssen 92190 Meudon, France
4. Caltech Astronomy, MC105-24, Pasadena, CA 91125, USA
5. Observatoire de Genève, Laboratoire d'Astrophysique de l'Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1290 Sauverny, Switzerland