1. Nicolaus Copernicus Astronomical Center; ul. Bartycka 18; 00-716; Warszawa; Poland
2. Nicolaus Copernicus Astronomical Center; Department of Astrophysics; ul. Rabiańska 8; 87-100; Toruń; Poland
3. Department of Physics and Astronomy; University of North Carolina; Campus Boc 3255; Chapel Hill; NC; 27599-3255; USA