1. Department of Astronomy, School of Physics , Peking University, Beijing 100871, China
2. Kavli Institute for Astronomy and Astrophysics, Peking University , Beijing 100871, China
3. CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences , 20A Datun Road, Chaoyang District, Beijing 100101, China
4. South-Western Institute for Astronomy Research, Yunnan University , Kunming, Yunnan 650091, China
5. Center for Astronomy and Space Sciences, China Three Gorges University , Yichang 443002, China
6. Shanghai Astronomical Observatory , 80 Nandan Road, Shanghai 200030, China