1. Central (Pulkovo) Astronomical Observatory, Russian Academy of Sciences , Pulkovskoye Chaussee 65/1, St Petersburg 196140 , Russia
2. Departamento de Astronomia, Instituto de Física, UFRGS , Avenida Bento Gonçalves 9500, Porto Alegre, RS , Brazil
3. Astrophysics department, Saint Petersburg State University , Universitetskij Pr. 28, St Petersburg 198504 , Russia
4. Special Astrophysical Observatory, Russian Academy of Sciences , Nizhnij Arkhyz 369167 , Russia
5. Department of Physics and Astronomy, Brigham Young University , N283 ESC, Provo, UT 84602 , USA
6. Department of Applied Mathematics, Saint Petersburg University of Aerospace Instrumentation , Bol. Morskaya ul. 67A, St Petersburg 190000 , Russia