1. Hamburger Sternwarte, University of Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany
2. Kwasan and Hida Observatories, Kyoto University, 17 Ohmine-cho Kita Kazan, Yamashina-ku, Kyoto, Kyoto 607-8471, Japan
3. Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, 3037-5 Honjou, Kamogata, Asakuchi, Okayama 719-0232, Japan
4. Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan