Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008;
Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008;
Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008;
Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008;
Qingdao Station of Purple Mountain Observatory, Qingdao 266003;
Qingdao Station of Purple Mountain Observatory, Qingdao 266003;
Qingdao Station of Purple Mountain Observatory, Qingdao 266003;