1. Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
2. Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA, Leiden, the Netherlands
3. Albert-Einstein-Institut, Max-Planck-Institut fúr Gravitationsphysik, D-30167 Hannover, Germany
4. Department of Astrophysics/IMAPP, Radboud University Nijmegen, POBox 9010, NL-6500 GL, Nijmegen, the Netherlands
5. Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
6. Department of Physics, University of Warwick, Coventry CV4 7AL, UK
7. Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DG, UK