[1] Penn State Univ, Dept Astron & Astrophys, Davey Lab 525, University Pk, PA 16802 USA
[2] Princeton Univ Observ, Princeton, NJ 08540 USA
[3] Univ Washington, Dept Astron, Seattle, WA 98195 USA
[4] Fermilab Natl Accelerator Lab, Batavia, IL 60510 USA
[5] Apache Point Observ, Sunspot, NM 88349 USA
[6] CALTECH, Dept Astron, Pasadena, CA 91125 USA
[7] European Space Agcy VILSPA, XMM Sci Operat Ctr, E-28080 Madrid, Spain
[8] USN Observ, Washington, DC 20392 USA
[9] Univ Chicago, Ctr Astron & Astrophys, Chicago, IL 60637 USA
[10] Max Planck Inst Extraterr Phys, D-85740 Garching, Germany