[1] Univ Turku, Dept Phys & Astron, FI-20014 Turku, Finland
[2] Armagh Observ & Planetarium, Coll Hill, Armagh BT61 9DG, North Ireland
[3] Univ Western Ontario, London, ON N6A 3K7, Canada
[4] Univ Svizzera Italiana, IRSOL Ist Ric Solari Aldo & Cele Dacco, Fac Informat, Via Patocchi 57, Locarno, Switzerland
[5] Univ Svizzera Italiana, Euler Inst, Fac Informat, Via Santa 1, CH-6962 Lugano, Switzerland
[6] Inst Sonnenphys KIS, Georges Kohler Allee 401A, D-79110 Freiburg, Germany