1. Purple Mountain Observatory, the Partner Group of MPI für Astronomie, 8 Yuanhua Road, Nanjing 210034, China
2. School of Astronomy and Space Sciences, University of Science and Technology of China, Hefei 230029, China
3. Graduate School, University of the Chinese Academy of Science, 19A Yuquan Road, Beijing 100049, China
4. South-Western Institute for Astronomy Research, Yunnan University, Kunming 650500, China
5. Department of Astronomy, School of Physics, Peking University, Beijing 100871, China