1. Astronomical Observatory, Volgina 7, P.O. Box 74, 11060 Belgrade, Serbia
2. Department of Theoretical Physics and Condensed Matter Physics (020), Vinča Institute of Nuclear Sciences-National Institute of the Republic of Serbia, University of Belgrade, P.O. Box 522, 11001 Belgrade, Serbia
3. Bogoliubov Laboratory for Theoretical Physics, Joint Institute for Nuclear Research, 141980 Dubna, Russia