1. Cahill Center
for Astronomy
and Astrophysics 301-17, California Institute of Technology, Pasadena, California 91125, United States
2. Department of Astronomy, University of Michigan, 933 Dennison Building, Ann
Arbor, Michigan 48109, United States
3. I. Physicalisches Institut der Universität zu Köln, Zülpicher
Straße 77, 50937 Köln, Germany
4. Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The
Netherlands and Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany