1. Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
2. Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599-3255, USA
3. Department of Physics, University of Warwick, Coventry CV4 7AL, UK
4. National Astronomical Research Institute of Thailand, 191 Siriphanich Bldg., Huay Kaew Road, Chiang Mai 50200, Thailand
5. Instituto de Astrofísica de Canarias, Vía Lactea s/n, La Laguna, E-38205 Tenerife, Spain
6. Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
7. South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, South Africa
8. Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
9. Department of Astronomy, University of Texas at Austin, Austin, TX 78712, USA
10. McDonald Observatory, Fort Davis, TX 79734, USA
11. Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, Norman, OK 73019, USA