1. Institut für theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg, Albert-Ueberle Str. 2, D-69120 Heidelberg, Germany
2. Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
3. Laboratoire AIM, CEA/DSM – CNRS – Université Paris Diderot, Irfu/Service d’Astrophysique, CEA Saclay, F-91191 Gif-sur-Yvette, France
4. University of Cincinnati, Clermont College, Batavia, OH 45103, USA
5. School of Physics and Astronomy, Queen's Buildings, The Parade, Cardiff University, Cardiff CF24 3AA, UK