1. Faculty of Physics, Ludwig-Maximilians-Universität, Scheinerstr 1, D-81679 Munich, Germany
2. ASTRON, the Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, NL-7991 PD Dwingeloo, the Netherlands
3. INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (CA), Italy
4. Astronomy Research Unit, University of Oulu, Pentti Kaiteran katu 1, FI-90014 Oulu, Finland
5. Kapteyn Astronomical Institute, University of Groningen, PO Box 72, NL-9700 AB Groningen, the Netherlands
6. Centre for Space Research, North-West University, Potchefstroom 2520, South Africa
7. INAF – Astronomical Observatory of Capodimonte, via Moiariello 16, I-80131 Napoli, Italy