1. Jodrell Bank Centre for Astrophysics, Alan Turing Building, Manchester, M13 9PL, UK
2. Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
3. Koninklijke Sterrenwacht van België, Ringlaan 3, B-1180 Brussels, Belgium
4. Laboratoire Lagrange, Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, boulevard de l’Observatoire, CS 34229, F-06304 Nice Cedex 4, France
5. University of North Carolina Chapel Hill, Chapel Hill, NC 20599-3255, USA
6. Department of Physics & Laboratory for Space Research, University of Hong Kong, Pokfulam Road, Hong Kong