1. University of Belgrade, Institute of Physics, PO Box 57, 11001 Belgrade, Serbia
2. Isaac Newton Institute of Chile, Yugoslavia Branch, Volgina 7, 11060 Belgrade, Serbia
3. Astronomical Observatory, Volgina 7, 11060 Belgrade 38, Serbia
4. Sorbonne Université, Observatoire de Paris, Université PSL, CNRS,LERMA, F-92190 Meudon, France