1. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China
2. Key Laboratory of Dark Matter and Space Astronomy, Chinese Academy of Sciences, Nanjing 210008, China
3. Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education, Nanjing 210093, China
4. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, NL-9700 AV Groningen, The Netherlands
5. Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Xinjiang 830011, China
6. Department of Astronomy, Nanjing University, Nanjing 210093, China
7. Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China