1. Yunnan Observatories, Chinese Academy of Sciences, Kunming 650216, China
2. Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences, Kunming 650216, China
3. University of Chinese Academy of Sciences, Beijing 100049, China
4. Department of Astronomy, University of Florida, Bryant Space Science Center, Gainesville, FL 32611, USA
5. Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science and Technology of China, Chinese Academy of Sciences, Hefei 230026, China
6. Department of Astronomy and Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093, China
7. Hamburger Sternwarte, Universität Hamburg, Hamburg 21029, Germany