ZEEMAN-EFFECT OBSERVATIONS OF H-I EMISSION PROFILES .1. MAGNETIC-FIELD LIMITS FOR 3 REGIONS BASED ON OBSERVATIONS CORRECTED FOR POLARIZED BEAM STRUCTURE

Magnetic field mapping of three H I features, toward MBM 12, MBM 40, a nd H0928+02, was attempted using 21 cm Zeeman effect observations corr ected for sidelobe signals. A detailed description of errors introduce d into the observations through interaction between H I brightness str ucture around the source direction and polarized beam structure is giv en. After corrections were applied to the data, no unambiguous magneti c field effects were found. The previous claim by this author of a hel d toward NPS 20, associated with MBM 40, is not confirmed. For each ma pped area the individual held fits were averaged, and the results indi cate 0.25+/-0.12 mu G for the MBM 40 region (error 1 sigma), 0.48+/-0. 31 mu G for H0928+02, and -0.29+/0.38 mu G for those directions toward MBM 12 where the data were judged to be reliable. The implied upper l imits of 0.36 mu G for the MBM 40 region and less than 1.0 mu G for th e other two suggest that the magnetic field strength in diffuse H I ob served with a 22' beam is far lower than has heretofore been recognize d.