School of Space Science and Physics;
Shandong University at Weihai;
Weihai 264209;
China;
Zentrum ftir Astronomie der Universitat Heidelberg;
Landessternwarte;
Konigstuhl 12;
D-69117Heidelberg;
Germany;
Key Laboratory of Optical Astronomy;
National Astronomical Observatories;
Chinese Academy of Sciences;
Beijing 100012;
China;