1 Astrophysics Research Institute, Liverpool John Moores University, IC2 Liverpool Science Park, Liverpool, L3 5RF, UK e-mail: M.J.Darnley@ljmu.ac.uk 2 Institut de Ciencies de l’Espai (CSIC-IEEC), Campus UAB, C/Can Magrans s/n, 08193 Cerdanyola del Valles, Spain 3 Department of Astrophysics/IMAPP, Radboud University, PO Box 9010, 6500 GL Nijmegen, The Netherlands 4 Instituto de Astrofisica de Canarias, Via Lactea, s/n, La Laguna, 38205 Santa Cruz de Tenerife, Spain 5 Departamento de Astrofisica, Universidad de La Laguna, La Laguna, 38206 Santa Cruz de Tenerife, Spain 6 Department of Astronomy, San Diego State University, San Diego, CA 92182, USA 7 Physics Department, Lancaster University, Lancaster, LA1 4YB, UK 8 Department of Earth Science and Astronomy, College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, 153-8902 Tokyo, Japan 9 Astronomical Institute, Academy of Sciences, 251 65 Ondřejov, Czech Republic 10 Astronomy Department, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Urbana, IL 61801, USA 11 Department of Astronomy, Keio University, Hiyoshi, 223-8521 Yokohama, Japan 12 Variable Stars Observers League in Japan (VSOLJ), 7-1 Kitahatsutomi, 273-0126 Kamagaya, Japan 13 Astronomical Institute of the Charles University, Faculty of Mathemathics and Physics, V Holesovickach 2, 180 00 Praha 8, Czech Republic 14 Okayama Astrophysical Observatory, NAOJ, NINS, 3037-5 Honjo, Kamogata, Asakuchi, 719-0232 Okayama, Japan 15 European Space Astronomy Centre, Camino Bajo del Castillo s/n, Urb. Villafranca del Castillo, 28692 Villanueva de la Canada, Madrid, Spain 16 Departament de Fisica i Enginyeria Nuclear, EUETIB, Universitat Politecnica de Catalunya, c/ Compte d’Urgell 187, 08036 Barcelona, Spain 17 Institut d’Estudis Espacials de Catalunya, c/ Gran Capita 2-4, Ed. Nexus-201, 08034 Barcelona, Spain 18 Isaac Newton Group of Telescopes, Apartado de correos 321, 38700 Santa Cruz de La Palma, Spain