1. Department of Physics, ETH Zürich, CH-8093 Zürich, Switzerland
2. Leiden Observatory, Leiden University, PO Box 9513, NL-2300 RA Leiden, the Netherlands
3. Leibniz-Institut für Astrophysik Potsdam, AIP, An der Sternwarte 16, D-14482 Potsdam, Germany
4. Univ Lyon, Univ Lyon1, Ens de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69230 Saint-Genis-Laval, France
5. CNRS/IRAP, 9 Avenue Colonel Roche, F-31400 Toulouse, France