1. NASA/Goddard Space Flight Center, Code 693, Greenbelt, MD 20771, USA.
2. Science Systems and Applications, 5900 Princess Garden Parkway, Suite 300, Lanham, MD 20706, USA.
3. Department of Astronomy, Cornell University, Ithaca, NY 14853, USA.
4. Department of Astronomy, University of Maryland, College Park, MD 20742, USA.
5. Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique (LESIA), CNRS–Unité Mixte de Recherche (UMR) 8109, Observatoire de Paris, 5 place Jules Janssen, F-91925 Meudon Cedex, France.