1. Instituto de Astronomía y Ciencias Planetarias, Universidad de Atacama, Copayapu 485, Copiapó 1531772, Chile
2. Institute of Physics, Southern Federal University, Stachki 194, 344090 Rostov-on-Don, Russia
3. Dipartimento di Fisica e Astronomia, Universitá di Padova, Vicolo Osservatorio 3, I-35122 Padova, Italy