1. Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
2. SUPA, Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
3. Departamento de Astrofísica, Facultad de CC. Físicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain
4. Department of Physics, University of the Pacific, Stockton, CA 95211, USA
5. Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, CH-1290 Versoix, Switzerland
6. Herschel Science Centre, ESA, Villafranca del Castillo, Apartado 78, E-28691 Villanueva de la Cañada, Spain
7. Dipartimento di Fisica e Astronomia, Università di Padova, vicolo dell’Osservatorio 2, I-35122 Padova, Italy