1. Institute for Frontier in Astronomy and Astrophysics, Beijing Normal University , Beijing 102206 , China
2. Department of Astronomy, Beijing Normal University , Beijing 100875 , China
3. National Astronomical Observatories, Chinese Academy of Sciences , Beijing 100101 , China
4. Purple Mountain Observatory, Chinese Academy of Sciences , Nanjing 210023 , China
5. South-Western Institute for Astronomy Research, Yunnan University , Kunming 650500 , China