1. Leiden Observatory, Leiden University, P. O. Box 9513, 2300 RA Leiden, The Netherlands
2. Observatoire de Paris, LERMA and UMR 8112 du CNRS, 5 place Jules Janssen, 92195 Meudon, France
3. Department of Physics, Wellesley College, Wellesley, Massachusetts 02481, USA
4. Department of Physics and Astronomy, University of Toledo, Toledo, Ohio 43606, USA
5. Research School of Physics and Engineering, The Australian National University, ACT 0200 Canberra, Australia
6. School of Earth and Space Exploration, Arizona State University, 781 S. Terrace Rd, Tempe, Arizona 85281, USA
7. Synchrotron SOLEIL, Orme de Merisiers, St. Aubin, BP 48, 91192 Gif sur Yvette Cedex, France