Affiliation: | Department of Physics, Science Laboratories, South Road, Durham DH1 3LE;Anglo-Australian Observatory, PO Box 296, Epping, NSW 2121, Australia;Department of Physics, Oxford University, Keble Road, Oxford OX1 3RH;Liverpool John Moores University, 12 Quays House, Egerton Wharf, Birkenhead CH41 1LD |