1. Department of Physics, National Tsing Hua University , No. 101, Section 2, Kuang-Fu Road, Hsinchu City 30013, Taiwan (R.O.C.)
2. Department of Physics, National Chung Hsing University , No. 145, Xingda Road, South Dist., Taichung 40227, Taiwan (R.O.C.)
3. Institute of Astronomy, National Tsing Hua University , No. 101, Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan (R.O.C.)
4. Research School of Astronomy and Astrophysics, The Australian National University , Canberra, ACT 2611, Australia
5. Department of Astrophysical and Planetary Science, University of Colorado Boulder , CO 80309, USA