1. Main Astronomical Observatory, Academy of Sciences of the Ukraine , 27 Zabolotnoho, Kyiv 03143, Ukraine
2. Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences , Rabiańska 8, PL-87-100 Toruń, Poland
3. Instituto de Astrofísica de Canarias (IAC) , Calle Vía Láctea s/n, E-38200 La Laguna, Tenerife, Spain
4. Centre for Astrophysics Research, University of Hertfordshire , College Lane, Hatfield AL10 9AB, UK
5. Department ‘of Physics and Astronomy, University College London , London WC1E 6BT, UK