1. Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, NL-6500 GL Nijmegen, the Netherlands
2. Institute for Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
3. Leibniz-Institut für Astrophysik Potsdam, AIP, An der Sternwarte 16, D-14482 Potsdam, Germany