[1] Univ Hawaii, Inst Astron, Honolulu, HI 96822 USA
[2] Univ Chicago, Dept Astron & Astrophys, Chicago, IL 60637 USA
[3] Fermilab Natl Accelerator Lab, Batavia, IL 60510 USA
[4] NYU, Dept Phys, New York, NY 10003 USA
[5] Johns Hopkins Univ, Dept Phys & Astron, Baltimore, MD 21218 USA
[6] Univ Pittsburgh, Dept Phys & Astron, Pittsburgh, PA 15260 USA
[7] Univ Arizona, Steward Observ, Tucson, AZ 85721 USA
[8] Princeton Univ Observ, Princeton, NJ 08544 USA
[9] Univ Sussex, Sussex Astron Ctr, Brighton BN1 9QJ, E Sussex, England
[10] Univ Edinburgh, Royal Observ, Edinburgh EH9 3HJ, Midlothian, Scotland
[11] Carnegie Mellon Univ, Dept Phys, Pittsburgh, PA 15213 USA
[12] Drexel Univ, Dept Phys, Philadelphia, PA 19104 USA
[13] Apache Point Observ, Sunspot, NM 88349 USA
[14] Eotvos Lorand Univ, Dept Phys Complex Syst, H-1088 Budapest, Hungary
[15] Univ Tokyo, Inst Astron, Tokyo 113, Japan
[16] Univ Tokyo, Res Ctr Early Univ, Sch Sci, Tokyo, Japan
[17] Univ Michigan, Dept Phys, Ann Arbor, MI 48109 USA
[18] USN Observ, Flagstaff, AZ 86002 USA
[19] Univ Chicago, Enrico Fermi Inst, Chicago, IL 60637 USA