1. Special Astrophysical Observatory; Nizhniy Arkhyz; Karachai-Cherkessia; 369167; Russia
2. Astronomical Institute; St Petersburg State University; Universitetskii pr. 28; 198504; St Petersburg; Stary Peterhof; Russia
3. UCO/Lick Observatory; University of California-Santa Cruz; Santa Cruz; CA; 95064; USA
4. Department of Astronomy; California Institute of Technology; 1200 East California Boulevard, MC 249-17; Pasadena; CA; 91125; USA
5. Sternberg Astronomical Institute; Moscow State University; Universitetsky pr. 13; Moscow; 119991; Russia