[1] Max Planck Inst Extraterr Phys, D-85748 Garching, Germany
[2] Osserv Astron Roma, INAF, I-00040 Rome, Italy
[3] Osservatorio Astron Bologna, INAF, I-40127 Bologna, Italy
[4] Max Planck Inst Plasma Phys, D-85748 Garching, Germany
[5] Excellence Cluster Universe, D-85748 Garching, Germany
[6] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[7] European So Observ, D-85748 Garching, Germany