1. Department of Physics and Astronomy, University of Turku, FI-20014 Turku, Finland
2. Space Research Institute of the Russian Academy of Sciences, Profsoyuznaya Str. 84/32, Moscow 117997, Russia
3. Institut für Astronomie und Astrophysik, Universität Tübingen, Sand 1, D-72076 Tübingen, Germany
4. Leiden Observatory, Leiden University, NL-2300RA Leiden, the Netherlands
5. Pulkovo Observatory, Russian Academy of Sciences, Saint Petersburg 196140, Russia
6. Kazan (Volga region) Federal University, Kremlevskaya str. 18, 420008 Kazan, Russia
7. National Research University Higher School of Economics, Myasnitskaya 20, 101000 Moscow, Russia