[1] Observ Paris, LESIA CNRS UMR 8109, F-92195 Meudon, France
[2] Univ Calif San Diego, Ctr Astrophys & Space Sci, La Jolla, CA 92093 USA
[3] Aberystwyth Univ, Inst Math & Phys Sci, Aberystwyth SY23 3BZ, Ceredigion, Wales
[4] Univ Coll London, Mullard Space Sci Lab, Dorking RH5 6NT, Surrey, England
[5] Hungarian Acad Sci, Konkoly Observ, Budapest, Hungary
[6] Univ Buenos Aires, CONICET, Inst Astron & Fis Espacio, RA-1428 Buenos Aires, DF, Argentina