1. University Education Center, Ibaraki University, Mito 310-8512, Japan
2. National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
3. Center for Astrophysics, Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, U.S.A.
4. Department of Astronomy, Graduate School of Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
5. Department of Physics, Soongsil University, Seoul 156-743, Korea