1. Department of Physics, University of Michigan , Ann Arbor, MI 48109 , USA
2. Leinweber Center for Theoretical Physics, University of Michigan , 450 Church St, Ann Arbor, MI 48109 , USA
3. Shanghai Astronomical Observatory, Chinese Academy of Sciences , Shanghai, 200030 , China
4. Purple Mountain Observatory, Chinese Academy of Sciences , Nanjing, 210034 , China
5. Astronomical Research Center, Shanghai Science & Technology Museum , Shanghai, 201306 , China