1. Leiden Observatory, Leiden University, NL-2300RA Leiden, The Netherlands
2. Space Research Institute of the Russian Academy of Sciences, Profsoyuznaya Str. 84/32, Moscow 117997, Russia
3. P. G. Demidov Yaroslavl State University, Sovietskaya 14, 150003 Yaroslavl, Russia
4. Sobolev Astronomical Institute, Saint Petersburg State University, Saint-Petersburg 198504, Russia