1. Pennsylvania State University, Department of Astronomy and Astrophysics, University Park, Pennsylvan
2. The University of Arizona, Department of Astronomy and Steward Observatory, Tucson, Arizona
3. California Institute of Technology, Department of Astronomy, Pasadena, California
4. National Institute of Standards and Technology, Time and Frequency Division, Boulder, Colorado
5. Carleton College, Department of Physics and Astronomy, Northfield, Minnesota