1. Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333 CA Leiden, the Netherlands
2. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, NL-9700 AV Groningen, the Netherlands
3. SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
4. National Centre for Nuclear Research, Astrophysics Division, PO Box 447, PL-90-950 Lodz, Poland
5. Center for Cosmology and Particle Physics, New York University, 726 Broadway, New York, NY 10003, USA
6. School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
7. Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, 05508-090 São Paulo, Brazil
8. Argelander-Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn, Germany
9. Department of Physics and Astronomy, University of Louisville, Louisville, KY 40292, USA
10. Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544, USA
11. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK