1. Department of Theoretical Physics and Astrophysics, Masaryk University, Kotlářská 2, CZ-611 37 Brno, Czech Republic
2. Bundesdeutsche Arbeitsgemeinschaft für Veränderliche Sterne e.V. (BAV), Munsterdamm 90, 12169 Berlin, Germany
3. American Association of Variable Star Observers (AAVSO), Cambridge, 49 Bay State Rd, MA 02138, USA
4. Institute of Physics, Faculty of Science, P. J. Šafárik University, Park Angelinum 9, Košice 040 01, Slovak Republic
5. Astronomical Institute of the Slovak Academy of Sciences, 059 60 Tatranská Lomnica, Slovak Republic