1. Department of Physics, University of Warwick , Coventry CV4 7AL , UK
2. Department of Physics and Astronomy, University College London , Gower Street, London WC1E 6BT , UK
3. Center for Astrophysics and Space Sciences, University of California , San Diego, CA 92093-0424 , USA
4. Département de Physique, Université de Montréal , C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7 , Canada
5. Trottier Institute for Research on Exoplanets, Université de Montréal , C.P. 6128 Succ. Centre-ville, Montréal, QC H3C 3J7 , Canada
6. School of Earth and Space Exploration, Arizona State University , Tempe, AZ 85287-1404 , USA
7. Institut für Theoretische Physik und Astrophysik, University of Kiel , D-24098 Kiel , Germany
8. Department of Scientific Research , Beijing Planetarium, Xizhimenwai Street, Beijing 100044 , China