1. University of Belgrade, Institute of Physics, P. O. 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, Serbia
4. LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universites, UPMC (Univ. Pierre, and Marie Curie) Paris 06, 5 Place Jules Janssen, 92190 Meudon, France