1. Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, ul. Grudziadzka 5/7, PL-87-100 Torun, Poland
2. Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
3. Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland