1. SISSA, Via Bonomea 265, I-34136 Trieste, Italy
2. IFPU, Institute for Fundamental Physics of the Universe, via Beirut 2, I-34151 Trieste, Italy
3. INFN, Sezione di Trieste, Via Bonomea 265, I-34136 Trieste, Italy
4. INAF, Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34143 Trieste, Italy