1. Astrophysics Group, Keele University , Staffordshire ST5 5BG, UK
2. Space Telescope Science Institute , 3700 San Martin Dr, Baltimore, MD 21218, USA
3. Institute of Astronomy, University of Cambridge , Madingley Road, Cambridge CB3 0HA, UK
4. European Southern Observatory (ESO), Av. Alonso de Córdova 3107, 763 0355 Vitacura, Santiago, Chile
5. Observatoire Astronomique de l’Universitéde Genéve , Chemin Pegasi 51, Versoix, CH-1290 Versoix, Switzerland
6. Department of Physics, University of Rome ‘Tor Vergata’ , Via della Ricerca Scientifica 1, I-00133 Rome, Italy
7. Max Planck Institute for Astronomy , Königstuhl 17, D-69117 Heidelberg, Germany
8. INAF, Osservatorio Astrofisico di Torino , Via Osservatorio 20, I-10025 Pino Torinese, Italy