Institution: | (1) Instituto di Fisica cosmica del C.N.R., Milano, Italy;(2) Astronomical Institute, Ondrejov, Czechoslovakia;(3) Sterrewacjt Sonnenborgh, Utrecht, The Netherlands;(4) University of Calgary, Calgary, Alberta, Canada;(5) Laboratory for Space Research, Utrecht, The Netherlands;(6) Ondrejov observatory, Czechoslovakia |