1. The California Institute of Technology, Pasadena 91125.
2. The Jet Propulsion Laboratory, California Institute of Technology, Pasadena 91011
3. The Jet Propulsion Laboratory, California Institute of Technology, Pasadena 91011., (National Research Council resident research associate).
4. Kitt Peak National Observatory, Tucson, Arizona 85725.
5. NASA Goddard Space Flight Center, Greenbelt, Maryland 20771.
6. Cornell University, Ithaca, New York 14853.
7. The University of Arizona, Tucson 85721.