1. St. Petersburg State University, Universitetskij pr. 28, 198504 St Petersburg, Stary Peterhof, Russia
2. Central (Pulkovo) Astronomical Observatory of RAS, Pulkovskoye Chaussee 65/1, 196140 St Petersburg, Russia
3. Special Astrophysical Observatory, Nizhniy Arkhyz, 369167 Karachai-Cherkessia, Russia