1. Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, D-21029 Hamburg, Germany
2. School of Earth and Space Exploration, Arizona State University, P.O. Box 876004, Tempe, AZ, USA
3. Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia
4. Center for Computational Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan