[1] Instituto de Astrofísica de Canarias (IAC), C/ vía Láctea s/n, 38200 La Laguna, Spain
[2] Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, United Kingdom
[3] Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, United Kingdom
[4] Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 877, 22800 Ensenada, B.C., Mexico
[5] Isaac Newton Group of Telescopes, Ap. de Correos 321, 38700 Sta. Cruz de la Palma, Spain
[6] Department of Physics, Macquarie University, NSW 2109, Australia
[7] Institut für Physik, Karl-Franzens Universität Graz, Universitätsplatz 5, 8010 Graz, Austria
[8] Astrophysics Group, Department of Physics, Bristol University, Tyndall Avenue, Bristol BS8 1TL, United Kingdom
[9] Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Oxford Road, M13 9 PL Manchester, United Kingdom
[10] Centre for Astrophysics Research, University of Hertfordshire, College Lane Campus, Hatfield AL10 9AB, United Kingdom
[11] Anglo-Australian Observatory, PO Box 296, Epping, NSW 1710, Australia
[12] Departamento de Astrofísica, Universidad de la Laguna, 38205 La Laguna, Tenerife, Spain
[13] Centro Astronómico Hispano Alemán, Calar Alto, C/Jesús Durbán Remón 2-2, 04004 Almeria, Spain
[14] Centro de Estudios de Física Del Cosmos de Aragón (CEFCA), C/General Pizarro 1-1, 44001 Teruel, Spain