1. Astronomy Unit, Department of Physics, University of Trieste , via Tiepolo 11, I-34131 Trieste , Italy
2. INAF- Astronomical Observatory of Trieste , via Tiepolo 11, I-34143 Trieste , Italy
3. IFPU – Institute for Fundamental Physics of the Universe , Via Beirut 2, I-34014 Trieste , Italy
4. Department of Space, Earth & Environment, Chalmers University of Technology , SE-41296 Gothenburg , Sweden
5. INFN, Sezione di Trieste , I-34149 Trieste , Italy
6. Dept. of Astronomy, University of Virginia , Charlottesville, VA 22904 , USA