Institution: | Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT;Department of Astronomy, Peking University, Beijing 100871, P.R. China;Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA;Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, NY 10024, USA |