[1] CNR, Ist Sistemi Complessi, Via Madonna Piano 10, I-50019 Sesto Fiorentino, Italy
[2] INFN Firenze, Via G Sansone 1, I-50019 Sesto Fiorentino, Italy
[3] Univ Firenze, Dipartimento Fis & Astron, Sez Astrofis & Sci Spazio, Piazzale E Fermi 2, I-50125 Florence, Italy
[4] INAF Firenze, Piazzale E Fermi 5, I-50125 Florence, Italy
[5] Univ Padua, Dipartimento Fis & Astron Galileo Galilei, Vicolo Osservatorio 3, I-35122 Padua, Italy
[6] INFN Padova, Via Marzolo 8, I-35131 Padua, Italy
[7] Padova Astron Observ, INAF, Vicolo Osservatorio 5, I-35122 Padua, Italy
[8] INAF Bologna, Via Gobetti 93-3, I-40129 Bologna, Italy
[9] Univ Bologna, Dipartimento Fis & Astron Augusto Righi, Alma Mater Studiorum, Via Gobetti 93-2, I-40129 Bologna, Italy