1. Kapteyn Astronomical Institute, University of Groningen, PO BOX 800, NL-9700 AV Groningen, the Netherlands
2. Physics & Astronomy, University of Southampton, Southampton, Hampshire SO17 1BJ, UK
3. Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, 650216 Kunming, PR China
4. Center for Astronomical Mega-Science, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing, 100012, P. R. China
5. Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate, Italy
6. Departament de Física, EEBE, Universitat Politècnica de Catalunya, Av. Eduard Maristany 16, E-08019 Barcelona, Spain
7. Institute of Space Studies of Catalonia (IEEC), E-08034 Barcelona, Spain
8. Dipartimento di Fisica, Universitá degli Studi di Cagliari, SP Monserrato-Sestu km 0.7, I-09042 Monserrato, Italy
9. University of Oxford, Department of Physics, Astrophysics Denys Wilkinson Building Keble Road, Oxford OX1 3RH, UK
10. Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450, USA