1. Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str 1, D-85741 Garching, Germany
2. Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
3. Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
4. Leibniz Institute for Astrophyics Potsdam (AIP), Ander Sternwarte 16, D-14482 Potsdam, Germany
5. School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK
6. Department of Astronomy, Yale University, New Haven, CT 06520, USA