1. UK Astronomy Technology Centre, Royal Observatory Edinburgh , Blackford Hill, Edinburgh EH9 3HJ, UK
2. Department of Physics and Astronomy, University of Sheffield , Hounsfield Road, Sheffield S3 7RH, UK
3. Université de la Côte d’Azur , Observatoire de la Côte d’Azur, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, F-06304 Nice cedex 4, France
4. Jeremiah Horrocks Institute, University of Central Lancashire , Preston PR1 2HE, UK
5. ASTRON , P.O. Box 2, NL-7990 AA Dwingeloo, the Netherlands
6. Kapetyn Astronomical Institute, University of Groningen , Postbuss 800, NL-9700 AV Groningen, the Netherlands
7. Instituto de Astrofisica de Canarias , Calle Via Láctea, E-38205 La Laguna, Tenerife, Spain
8. Departamento de Astrofisica, Universidad de La Laguna , E-38206 La Laguna, Tenerife, Spain