[1] Johns Hopkins Univ, Bloomberg Ctr, Dept Phys & Astron, Baltimore, MD 21218 USA
[2] Tsinghua Univ, Dept Astron, Beijing 100084, Peoples R China
[3] Leiden Univ, Leiden Observ, POB 9513, NL-2300 RA Leiden, Netherlands
[4] Princeton Univ, Inst Adv Study, Princeton, NJ 08544 USA
[5] Drexel Univ, Dept Phys, 32 S 32nd St, Philadelphia, PA 19104 USA
[6] UC Santa Barbara, Dept Phys, Broida Hall, Santa Barbara, CA 93106 USA
[7] US Naval Acad, Dept Phys, 572 CHolloway Rd, Annapolis, MD 21402 USA