1. Space Research and Planetary Sciences Division, Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
2. Lucerne University of Applied Sciences and Arts, Technikumstrasse 21, 6048 Horw, Switzerland
3. Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, 221 00 Lund, Sweden