1. Department of Mathematics and Physics ‘E. De Giorgi’, University of Salento, Via per Arnesano, CP-I93, I-73100 Lecce, Italy
2. INFN, Sezione di Lecce, Via per Arnesano, CP-193, I-73100 Lecce, Italy
3. R.P. Feynman Observatory, Gagliano del Capo, I-73034 Lecce, Italy
4. CBA, Center for Backyard Astrophysics - Gagliano del Capo, I-73034, Lecce, Italy
5. Sternberg Astronomical Institute, Moscow State University, Moscow 119991, Russia
6. Astronomical Institute of the Slovak Academy of Sciences, Tatranska Lomnica 05960, Slovakia