1. Yunnan Observatories, Chinese Academy of Sciences (CAS), Kunming 650216, China
2. Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650011, China
3. Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
4. Aarhus Institute of Advanced Studies (AIAS), Aarhus University, Høegh-Guldbergs Gade 6B, DK-8000 Aarhus C, Denmark
5. University of the Chinese Academy of Sciences, Yuquan Road 19, Shijingshan Block, Beijing 100049, China
6. Center for Astronomical Mega-Science, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, China