[1] Univ Calif Davis, Dept Phys & Astron, One Shields Ave, Davis, CA 95616 USA
[2] Univ Calif Los Angeles, Dept Phys & Astron, 430 Portola Plaza, Los Angeles, CA 90095 USA
[3] Univ Arizona, Steward Observ, Tucson, AZ 85721 USA
[4] European Southern Observ, Karl Schwarzschild Str 2, D-85748 Garching, Germany
[5] Univ Calif Riverside, Dept Phys & Astron, 900 Univ Ave, Riverside, CA 92521 USA
[6] Univ Edinburgh, Inst Astron, James Clerk Maxwell Bldg,Peter Guthrie Tait Rd, Edinburgh EH9 3FD, Scotland
[7] Max Planck Inst Extraterr Phys, Postfach 1312, D-85741 Garching, Germany
[8] Leiden Univ, Leiden Observ, POB 9513, NL-2300 AA Leiden, Netherlands
[9] Univ Calif San Diego, Ctr Astrophys & Space Sci, 9500 Gilman Dr, La Jolla, CA 92093 USA