1. Astronomical Observatory, Volgina 7, 11060 Belgrade 38, Serbia
2. Observatoire de Paris, Sorbonne Université, Université PSL, CNRS, F-92195 Meudon, France
3. Isaac Newton Institute of Chile, Yugoslavia Branch, Volgina 7, 11060 Belgrade, Serbia
4. Institute of Physics Belgrade, University of Belgrade, P.O. Box 57, 11001 Belgrade, Serbia