Key Laboratory of Dark Matter and Space Astronomy;
Purple Mountain Observatory;
Chinese Academy of Sciences;
Nanjing 210033;
China;
School of Astronomy and Space Science;
University of Science and Technology of China;
Hefei 230026;
China;
Leibniz-Institut fur Astrophysik Potsdam(AIP);
An der Sternwarte 16;
14482 Potsdam;
Germany;