[1] Univ Seville, Dept Fis Atom Mol & Nucl, E-41080 Seville, Spain
[2] CSIC, Inst Astrofis Andalucia, E-18080 Granada, Spain
[3] Univ Calif Santa Cruz, Dept Phys, Santa Cruz, CA 95064 USA
[4] Univ Calif Santa Cruz, Dept Astron & Astrophys, UCO Lick Observ, Santa Cruz, CA 95064 USA
[5] SISSA, I-34136 Trieste, Italy
[6] Space Telescope Sci Inst, Baltimore, MD 21218 USA
[7] Univ Complutense Madrid, Fac CC Fis, Dept Astrofis, E-28040 Madrid, Spain
[8] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[9] Univ Calif Berkeley, Dept Astron, Berkeley, CA 94720 USA
[10] Univ Western Ontario, Dept Phys & Astron, London, ON N6A 3K7, Canada
[11] Univ Nottingham, Sch Phys & Astron, Nottingham NG7 2RD, England
[12] Univ Pittsburgh, Dept Phys & Astron, Pittsburgh, PA 15260 USA
[13] Univ Arizona, Steward Observ, Tucson, AZ USA