1. Leiden Observatory, Leiden University, Post Office Box 9513, 2300 RA Leiden, Netherlands.
2. Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA.
3. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA.
4. Astronomical Institute Anton Pannekoek, University of Amsterdam, 1098 XH Amsterdam, Netherlands.
5. Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA.
6. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA.
7. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA.
8. European Southern Observatory, 85748 Garching, Germany.
9. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA.
10. Max-Planck-Institut für Extraterrestrische Physik, 85748 Garching, Germany.