[1] Departement of Physics, Faculty of Materials Science and Technology, Slovak University of Technology in Bratislava, Paulfnska 16, 91724 Trnava, Slovakia
[2] Institut d'Astrophysique de Paris, 98 bis boulevard Arago, 75014 Paris, France
[3] Departement of Astronomy and Astrophysics, Penn State University, 525 Davey Lab., University Park, PA 16802-6305, United States
[4] School of Physics, University of Sydney, 2006, Australia
[5] Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovakia
[6] Nicholas Copernicus Observatory and Planetarium in Brno, Kraví Hora 2, 61600 Brno, Czech Republic