1. INAF - Osservatorio Astrofisico di Torino, I-10025 Pino Torinese, Italy
2. Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK
3. Institute of Astronomy of V.N. Karazin Kharkiv National University, Sumska Str. 35, Kharkiv UA-61022, Ukraine