1. School of Astronomy and Space Science, Nanjing University , Nanjing 210093, China
2. Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education , Nanjing 210093, China
3. Collaborative Innovation Center of Modern Astronomy and Space Exploration , Nanjing 210093, China
4. Apache Point Observatory and New Mexico State University , PO Box 59, Sunspot, NM 88349-0059, USA
5. Sternberg Astronomical Institute, Moscow State University , Moscow 119992, Russia
6. Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory , Nandan Road 80, Shanghai 200030, China
7. Department of Physics and Astronomy, University of Utah , 115 S. 1400 E., Salt Lake City, UT 84112, USA