[1] ESA, Div Astrophys, ISO Sci Operat Ctr, Villafranca, Spain
[2] Observ Paris Meudon, F-92195 Meudon, France
[3] CALTECH, Jet Prop Lab, Pasadena, CA USA
[4] Max Planck Inst Aeron, Katlenburg Lindau, Germany
[5] Univ London Queen Mary & Westfield Coll, London E1 4NS, England