1. Dublin Institute for Advanced Studies, Astronomy & Astrophysics Section, DIAS Dunsink Observatory , Dublin D15 XR2R , Ireland
2. Centre for Space Research, North-West University , Potchefstroom 2520 , South Africa
3. Astronomical Observatory of Ivan Franko National University of Lviv , Kyryla i Methodia 8, 79005 Lviv , Ukraine