1. Astronomy Department, University of California, Berkeley 94720, USA.
2. National Radio Astronomy Observatory, Green Bank, WV 24944, USA.
3. Universitat Bonn, 53121 Bonn, Germany.
4. Max-Planck-Institut für Radioastronomie, 53121 Bonn, Germany.
5. Commonwealth Scientific and Industrial Research Organization, Epping, New South Wales 2121, Australia.
6. Jet Propulsion Laboratory, Pasadena, CA 91109, USA.
7. Naval Research Laboratory, Code 7210, Washington, DC 20375, USA.
8. Dominion Radio Astrophysical Observatory, National Research Council, Penticton, British Columbia V2A 6K3, Canada.
9. Netherlands Foundation for Research in Astronomy, 7990 AA Dwingeloo, Netherlands.
10. Leiden University, 2300 RA Leiden, Netherlands.
11. New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA.
12. School of Physics, University of Sydney, New South Wales 2006, Australia.
13. Astrophysical, Planetary, and Atmospheric Sciences, Boulder, CO 80309, USA.
14. Observatoire de Paris, 92195 Meudon, France.