1. Department of Physics, Virginia Tech, Blacksburg, VA 24061, USA
2. Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
3. Astronomy Department, University of Washington, WA 98195, USA
4. Haverford College, Haverford, PA 19041, USA
5. The Observatories of the Carnegie Institution for Science, 813 Santa Barbara St, Pasadena, CA 91101, USA
6. Department of Astronomy, Peking University, Beijing 100871, China
7. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China