1. INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello, 16, I-80131 Napoli, Italy
2. European Southern Observatory, Karl-Schwarschild-Str. 2, D-85748 Garching, Germany
3. Kapteyn Astronomical Institute, University of Groningen, PO Box 800, NL-9700 AV Groningen, the Netherlands
4. Max Planck Institute for Extraterrestrial Physics, Karl-Schwarzschild-Str. 1, D-85741 Garching, Germany
5. INAF-Osservatorio Astronomico di Teramo, via Maggini, I-64100 Teramo, Italy
6. Dip. di Fisica, Universitad́i Napoli Federico II, C.U. di Monte Sant’Angelo, Via Cintia, I-80126 Naples, Italy