1. Department of Physics, Institute for Astronomy, ETH Zurich, CH-8093 Zurich, Switzerland.
2. Istituto Nazionale di Astrofisica (INAF) Osservatorio Astronomico di Padova, Vicolo dell Osservatorio 5, I-35122 Padova, Italy.
3. Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, D-85748 Garching, Germany.
4. INAF Osservatorio Astronomico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze, Italy.
5. Racah Institute of Physics, The Hebrew University, Jerusalem 91904, Israel.
6. Department of Astronomy, Campbell Hall, University of California, Berkeley, CA 94720, USA.
7. Department of Physics, Le Conte Hall, University of California, Berkeley, CA 94720, USA.
8. Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA.
9. INAF Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna, Italy.