1. INAF/Osservatorio Astrofisico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese, Italy
2. Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen, Denmark
3. Helmholtz-Zentrum Dresden-Rossendorf, D-01328 Dresden, Germany
4. Abastumani Astrophysical Observatory, Ilia State University, G. Tsereteli str 3, Tbilisi 0162, Georgia
5. Institute of Geophysics, Tbilisi State University, Aleksidze str 1, Tbilisi 0193, Georgia
6. Dipartimento di Fisica, Università degli Studi di Torino, Via Pietro Giuria 1, I-10125 Torino, Italy