1. School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK (SUPA)
2. Department of Physics, College of Science, University of Babylon, Hillah, Babylon, PO Box 4, Iraq
3. Instituto de Astrofísica de Canarias C/ Vía Láctea, s/n E-38205 La Laguna (Tenerife), Spain
4. Departamento de Astrofísica, Universidad de La Laguna, Calle Astrofísico Francisco Sánchez s/n, E-38205 La Laguna, Tenerife, Spain
5. Department of Physics, University of Helsinki, Gustaf Hällströmin katu 2a, FI-00014 Helsinki, Finland
6. Unbound, Unit 18, Waterside, 44-48 Wharf Road, London N1 7UX, UK
7. Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany
8. Department of Physics & Astronomy, Johns Hopkins University, Bloomberg Center, 3400 N. Charles St., Baltimore, MD 21218, USA