1. Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027, USA
2. Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY, UK
3. Observatories of the Carnegie Institution of Washington, 813 Santa Barbara St., Pasadena, CA 91101, USA
4. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
5. Center for Astrophysical Sciences, Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
6. Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
7. Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
8. Dipartimento di Fisica, Università di Roma Tor Vergata, via Della Ricerca Scientifica 1, I-00133, Roma, Italy
9. INAF, Rome Astronomical Observatory, via Frascati 33, I-00040, Monte Porzio Catone, Italy
10. Leibniz-Institüt für Astrophysik Potsdam, An der Sternwarte 16, D-14482, Potsdam, Germany
11. INAF-Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, I - 40129, Bologna, Italy
12. Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, Ca., 91125
13. Space Science Data Center - ASI, via del Politecnico, s.n.c., I-00133, Roma, Italy
14. Department of Astronomy & Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
15. Dipartimento di Fisica e Astronomia, Università di Bologna, Via Gobetti 93/2, I - 40129, Bologna, Italy
16. IPAC, Mail Code 314-6, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA
17. Department of Astronomy, University of Virginia, 530 McCormick Road, Charlottesville, VA 22904, USA
18. Department of Physics and Astronomy, Iowa State University, A313E Zaffarano, Ames, IA 50010, USA
19. National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
20. Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
21. Max Planck Institute for Astronomy, Konigstuhl 17, D-69117, Heidelberg, Germany
22. Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-2320, USA
23. Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland