1. Research School of Astronomy and Astrophysics, The Australian National University, ACT 2611, Australia
2. Center for Computational Science, Tsukuba University, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan
3. Department of Physics and Astronomy, University of Waterloo, Waterloo, ON N2L 2Y5, Canada