1. TAPIR, California Institute of Technology, Pasadena, CA 91125, USA
2. Department of Physics, Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3. Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str 1, D-85748 Garching, Germany
4. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
5. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
6. Department of Physics & Astronomy, University of Bologna, via Gobetti 93/2, I-40129 Bologna, Italy
7. Department of Astronomy, University of Florida, 211 Bryant Space Sciences Center, Gainesville, FL 32611, USA