1. Department of Astronomy, University of Wisconsin, 475 N. Charter Str., Madison, WI 53704, USA
2. INAF–Osservatorio di Padova, vicolo dell’ Osservatorio 5, I-35122 Padova, Italy
3. Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina
4. CONICET-Universidad de Buenos Aires, Instituto de Astronomía y Física del Espacio (IAFE), Av. Inte., Güiraldes 2620, C1428ZAA, Buenos Aires, Argentina
5. Universidad Nacional Arturo Jauretche, Av. Calchaquí 6200, F. Varela, Buenos Aires, Argentina
6. N. Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, PL 00-716 Warsaw, Poland
7. WIYN Observatory, Tucson, AZ 85719, USA
8. Dipartimento di Astronomia, Università di Padova, vicolo Osservatorio, 2, 35122 Padova, Italy
9. INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli
10. International Center for Relativistic Astrophysics, Piazzale della Repubblica, 2, 65122, Pescara, Italy
11. Department of Physics and Astronomy, Clemson University, Clemson, SC 29634, USA
12. Department of Physics, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa
13. INAF–Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy