1. Dipartimento di Fisica dell’ Università di Trieste, Sezione di Astronomia, via Tiepolo 11, I-34131 Trieste, Italy
2. INAF, Osservatorio Astronomico di Trieste, via Tiepolo 11, I-34131, Trieste, Italy
3. Departamento de Astronomía y Astrofísica, Universidad de Valencia, c/ Dr. Moliner, 50, E-46100 Burjassot (Valencia), Spain
4. INFN – National Institute for Nuclear Physics, Via Valerio 2, I-34127 Trieste, Italy
5. Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
6. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA