1. Center for AstrophysicsGuangzhou University Guangzhou China
2. Department of Physics and Astronomy “G. Galilei”University of Padova Padova Italy
3. Istituto Nazionale di Fisica Nucleare, Sezionedi Padova Padova Italy
4. Astronomy Science and Technology Research Laboratory of Department of Education of Guangdong ProvinceGuangzhou University Guangzhou China
5. Key Laboratory for Astronomical Observation and Technology of GuangzhouGuangzhou University Guangzhou China
6. Department of physics of School of physics and electronic informationAnhui Normal University Wuhu China