[1] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[2] Univ Washington, Dept Astron, Seattle, WA 98195 USA
[3] Space Telescope Sci Inst, Baltimore, MD 21218 USA
[4] Max Planck Inst Extraterr Phys, D-85741 Garching, Germany
[5] Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA
[6] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[7] Columbia Univ, Columbia Astrophys Lab, New York, NY 10027 USA
[8] Rutgers State Univ, Dept Phys & Astron, Piscataway, NJ 08854 USA
[9] Middlebury Coll, Dept Phys, Middlebury, VT 05753 USA
[10] Univ Evora, Dept Math, P-7000 Evora, Portugal
[11] Univ Vienna, Inst Astron, A-1180 Vienna, Austria
[12] Tel Aviv Univ, Raymond & Beverly Sackler Fac Exact Sci, Sch Phys & Astron, IL-69978 Tel Aviv, Israel
[13] Morehead State Univ, Ctr Space Sci, Morehead, KY 40351 USA