1. INAF – Astronomical Observatory of Capodimonte, via Moiariello 16, I-80131, Napoli, Italy
2. Department of Physics ‘E. Pancini’, University Federico II, via Cinthia 6, I-80126, Napoli, Italy
3. INFN section of Naples, via Cinthia 6, I-80126, Napoli, Italy