1. Universitäts-Sternwarte München, Scheinerstr 1, 81679 München
2. Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str 1, 85741 Garching, Germany
3. Department of Physics, University of Konstanz, Universitätsstr 10, 78457 Konstanz, Germany
4. Max Planck Institute for Extraterrestrial Physics, Giessenbachstr 1, 85748 Garching, Germany