1. UK Astronomy Technology Centre, Blackford Hill, Edinburgh EH9 3HJ, UK
2. National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
3. Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, London E1 4NS, UK
4. Department of Astronomy, University of California Berkeley, Berkeley, CA 94720, USA
5. Department of Physics and Astronomy, Texas Tech University, PO Box 41051, Lubbock, TX 79409, USA
6. Departamento de Astronomía, Universidad de Chile, Camino el Observatorio 1515, Las Condes, Santiago, Chile
7. Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany