1. Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706, USA
2. Osservatorio Astronomico di Trieste, Via G. B. Tiepolo, 11, I-34143 Trieste, Italy
3. School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
4. Department of Physics and Astronomy, University of California, 900 University Avenue, Riverside, CA 92507, USA
5. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
6. AURA for ESA, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
7. SISSA, International School for Advanced Studies, Via Bonomea 265, I-34136 Trieste, Italy
8. INFN, Sezione di Trieste, Via Valerio 2, I-34127 Trieste, Italy
9. IFPU, Institute for Fundamental Physics of the Universe, Via Beirut 2, I-34014 Trieste, Italy
10. Department of Astronomy and Astrophysics, The Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA