1. Department of Astronomy, Eötvös University, Pázmány Péter stny. 1/A, H-1118 Budapest, Hungary
2. Wigner Research Centre for Physics of HAS, PO Box 49, H-1525 Budapest, Hungary
3. Baja Astronomical Observatory of Szeged University, Szegedi út, Kt. 766, H-6500 Baja, Hungary
4. Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege Miklós út 15-17, H-1121 Budapest, Hungary