1. Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-106 91 Stockholm, Sweden
2. Instituto de Astrofisica de Canarias, Avda Via Lactea S/N, La Laguna, E-38205 Tenerife, Spain
3. Department of Physics and Astronomy, Uppsala University, 751 20 Uppsala, Sweden
4. Dipartimento di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino, Firenze, Italy
5. INAF–Osservatorio Astrofisico di Arcetri, I-50125 Firenze, Italy
6. Space Science and Astronomy, University of Oulu, PO Box 3000, FI-90014 Oulu, Finland
7. Departamento de Astrofísica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain
8. INAF, Osservatorio Astronomico di Padova, 35122 Padova, Italy