1. Max-Planck-Institut für Astronomie; Königstuhl 17; 69117; Heidelberg; Germany
2. Mullard Space Science Laboratory; University College London; Holmbury St. Mary; Dorking; Surrey; RH5 6NT
3. Jeremiah Horrocks Institute; University of Central Lancashire; Preston; PR1 2HE
4. Departamento de Física Teórica; Universidad Autónoma de Madrid; Cantoblanco; E-28049; Madrid; Spain
5. Institute for Theoretical Physics; University of Zürich; Winterthurerstrasse 190; CH-8057; Zürich; Switzerland
6. Department of Physics and Astronomy; McMaster University; Hamilton; Ontario; L8S 4M1; Canada
7. Astronomy Department; University of Washington; Box 351580; Seattle; WA; 98195-1580; USA