[1] CHALMERS UNIV TECHNOL,S-41296 GOTHENBURG,SWEDEN
[2] TECHNION ISRAEL INST TECHNOL,DEPT PHYS,IL-32000 HAIFA,ISRAEL
[3] KYOTO UNIV,DEPT ASTRON,SAKYO KU,KYOTO 60601,JAPAN
[4] CNRS,UPR 176,F-92195 MEUDON,FRANCE
[5] OBSERV PARIS,SECT MEUDON,DARC,F-92195 MEUDON,FRANCE