1. Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218–2686, USA.
2. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
3. Konkoly Observatory, Post Office Box 67, Budapest H–1525, Hungary.
4. European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile.
5. Laboratoire d'Astronomie Spatiale du CNRS, BP 8, 13376 Marseille, Cedex 12, France.
6. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA.
7. Department of Astronomy, University of Maryland, College Park, MD 20742, USA.
8. Institut d'Astrophysique, Université de Liège, B-4000 Liège, Belgium.
9. Space Physics Research Laboratory, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109–2143, USA.
10. Joint Astronomy Centre, Hilo, HI 96720, USA.
11. Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, F-31400, Toulouse, France.
12. European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching, Germany.
13. Space Telescope Science Institute, 3900 San Martin Drive, Baltimore, MD 21218, USA.
14. Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA.
15. Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Florence, Italy.