1. Thüringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany
2. Astronomical Institute, Czech Academy of Sciences, Fričova 298, CZ-25165 Ondřejov, Czech Republic
3. Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, D-50931 Köln, Germany
4. Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic