1. Yunnan Observatories, Chinese Academy of Sciences, PO Box 110, Kunming, Yunnan 650216, China
2. Center for Astronomical Mega-Science, Chinese Academy of Sciences, Beijing 100012, China
3. Key Laboratory of Modern Astronomy and Astrophysical, the Ministry of Education, Nanjing University, Nanjing, 210000, China
4. Smithsonian Astrophysical Observatory, 60 Garden Street, MS 15, Cambridge, MA 02138, US
5. Astrophysikalisches Institut Potsdam, D-14482 Potsdam, Germany