1. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
2. Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
3. School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
4. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
5. Eureka Scientific Inc., 2542 Delmar Avenue, Suite 100, Oakland, CA 94602-3017, USA
6. School of Mathematics and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, UK