1. Herzberg Astronomy and Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, British Columbia V9E 2E7, Canada
2. INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze, Italy
3. Space Science Data Center, ASI, via del Politecnico snc, I-00133 Roma, Italy
4. European Space Research and Technology Centre (ESA/ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, the Netherlands
5. Instituto de Astrofísica de Canarias, Calle Via Lactea, E-38205 La Laguna, Tenerife, Spain
6. Universidad de La Laguna, Dpto. Astrofísica, E-38206 La Laguna, Tenerife, Spain