E. Danezis (1), D. Nikolaidis (1), E. Lyratzi (1), L. \v{C}.
  Popovi\'c, M. S. Dimitrijevi\'c, A. Antoniou, E. Theodosiou ((1) University
  of Athens, Faculty of Physics, Section of Astrophysics, Astronomy and
  Mechanics, (2) Astronomical Observatory of Belgrade)