[1] AARHUS UNIV,INST PHYS & ASTRON,DK-8000 AARHUS C,DENMARK
[2] PRINCETON UNIV,DEPT PHYS,PRINCETON,NJ 08544
[3] UNIV CALIF SANTA CRUZ,LICK OBSERV,SANTA CRUZ,CA 95064
[4] CALTECH,JET PROP LAB,PASADENA,CA 91109
[5] NATL OPT ASTRON OBSERV,TUCSON,AZ 85726