1. Department of Physics, University of Warwick , Gibbet Hill Road, Coventry CV4 7AL , UK
2. Isaac Newton Group of Telescopes , Apartado de Correos 368, E-38700 Santa Cruz de La Palma , Spain
3. Department of Astronomy & Institute for Astrophysical Research, Boston University , 725 Commonwealth Avenue, Boston, MA 02215 , USA
4. Department of Physics and Astronomy, High Point University , High Point, NC 27268 , USA
5. Department of Physics and Astronomy, University of Sheffield , Sheffield S3 7RH , UK
6. Instituto de Astrofísica de Canarias , E-38205 La Laguna, Tenerife , Spain
7. Departamento de Astrofísica, Universidad de La Laguna , E-38206 La Laguna, Tenerife , Spain
8. Nordic Optical Telescope , Rambla José Ana Fernández Pérez 7, E-38711 Breña Baja , Spain
9. Instituto de Física, Universidade Federal do Rio Grande do Sul , Porto-Alegre, RS 91501-900 , Brazil
10. Department of Physics and Astronomy, University of North Carolina at Chapel Hill , Chapel Hill, NC 27599 , USA
11. Astronomical Observatory, University of Warsaw , Aleje Ujazdowskie 4, PL-00-478 Warszawa , Poland
12. Department of Physics, Astronomy, and Materials Science, Missouri State University , Springfield, MO 65897 , USA
13. Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA , UK
14. Department of Astrophysics, School of Physics and Astronomy, Tel Aviv University , Tel Aviv 6997801 , Israel
15. School of Physics, University College Cork , Cork, T12 ND89 Ireland
16. Jodrell Bank Centre for Astrophysics, University of Manchester , Manchester M13 9PL , UK
17. Department of Physics and Astronomy, Iowa State University , Ames, IA 50011 , USA
18. South African Astronomical Observatory , PO Box 9, Observatory 7935, Cape Town , South Africa