[1] ETH, Inst Astron, CH-8093 Zurich, Switzerland
[2] Univ Calif Los Angeles, Dept Phys & Astron, Los Angeles, CA 90025 USA
[3] Univ So Calif, Dept Phys & Astron, Los Angeles, CA 90089 USA
[4] Univ Louisville, Dept Phys & Astron, Louisville, KY 40292 USA
[5] Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544 USA