1. College of Physics and Electronics, Hunan Normal University, Changsha, Hunan 410081, China
2. Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA
3. Hunan Key Laboratory for Stellar and Interstellar Physics and School of Physics and Optoelectronics, Xiangtan University, Hunan 411105, China
4. College of Information Science and Engineering, Hunan Normal University, Changsha, Hunan 410081, China
5. Department of Astronomy, Beijing Normal University, Beijing 100875, China