[1] Univ Jyvaskyla, Dept Phys, POB 35 YFL, FI-40014 Jyvaskyla, Finland
[2] Univ Helsinki, Helsinki Inst Phys, FI-00014 Helsinki, Finland
[3] Univ Southern Denmark, Origins CP3, DK-5230 Odense M, Denmark
[4] Univ Southern Denmark, DIAS, DK-5230 Odense M, Denmark
[5] Univ Southampton, Dept Phys & Astron, Southampton SO17 1BJ, Hants, England