[1] Real Inst, Cadiz 11110, Spain
[2] Observ Armada, Secc Astron, Cadiz 11110, Spain
[3] CSIC, Inst Astrofis Andalucia, E-18080 Granada, Spain
[4] Danish Space Res Inst, DK-2100 Copenhagen O, Denmark
[5] INTA, Lab Astrofis Espacial & Fis Fundamental, Madrid 28080, Spain
[6] Univ Copenhagen, Astron Observ, DK-2100 Copenhagen O, Denmark
[7] European So Observ, D-85748 Garching, Germany
[8] Univ Oulu, Div Astron, Oulu 90014, Finland
[9] Inst Astrofis Canarias, Tenerife 38200, Spain
[10] Univ de la Coruna, Dept Ciencias Nevegac & Tierra, La Coruna 15011, Spain
[11] Michigan Technol Univ, Dept Phys, Houghton, MI 49931 USA
[12] Univ Nottingham, Sch Phys & Astron, Nottingham NG7 2RD, England
[13] Univ Toronto, Dept Astron, Toronto, ON M5S 3H8, Canada
[14] Space Telescope Sci Inst, Baltimore, MD 21218 USA
[15] Inst Astrophys, D-14482 Potsdam, Germany
[16] Osserv Astron Trieste, I-34131 Trieste, Italy
[17] Univ Amsterdam, NL-1098 SJ Amsterdam, Netherlands
[18] NASA, Goddard Space Flight Ctr, Greenbelt, MD 20771 USA
[19] CNR, Ist Astrofis Spaziale & Fis Cosm, Sez Bologna, I-40129 Bologna, Italy
[20] Thuringer Landessternwarte Tautenburg, D-07778 Tautenburg, Germany
[21] NASA, George C Marshall Space Flight Ctr, Huntsville, AL 35812 USA
[22] Clemson Univ, Clemson, SC 29634 USA
[23] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
[24] AF Ioffe Phys Tech Inst, St Petersburg 194021, Russia
[25] Lawrence Livermore Natl Lab, Livermore, CA 94550 USA
[26] Univ Hertfordshire, Dept Phys Sci, Hatfield AL10 9AB, Herts, England
[27] SUNY Stony Brook, Dept Phys & Astron, Stony Brook, NY 11794 USA
[28] Univ Arizona, Steward Observ, Tucson, AZ 85721 USA