University of Wales at Aberystwyth, Institute of Mathematical and Physical Sciences, Aberystwyth, SY23 3BZ United Kingdom; Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA
Bridgewater State College, Department of Physics, Bridgewater, MA 02325, USA
University of Illinois at Urbana-Champaign, Department of Physics, Urbana, IL 61801, USA
Observatoire Midi-Pyrenees, 14 Avenue d'Edouard Belin, Toulouse, F-31400 France
Jet Propulsion Lab, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA