1. Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany
2. ESO, European Southern Observatory, Karl-Schwarzschild Str 2, D-85748 Garching bei Muenchen, Germany
3. Univ Lyon, Univ Lyon 1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR 5574, F-69230 Saint-Genis Laval, France
4. ETH Zurich, Department of Physics, Wolfgang-Pauli-Str 27, CH-8093 Zurich, Switzerland