POLARIMETRIC MAPPING OF ORION USING MILLIPOL - MAGNETIC ACTIVITY IN BN KL

The spatial distribution of the polarized component of the thermal dust emission from the core of the Orion molecular cloud has been mapped over 15 positions at a wavelength of 1300-mu-m using the MILLIPOL instrument on the NRAO 12 m telescope. The chief findings of this study are three-fold. First, the polarization directions deduced for the map positions are quite similar, implying that the embedded magnetic field is strong (of the order of 1 mG) and uniform in direction over the core of the cloud. The angular dispersion, corrected for measurement uncertainty, is approximately 9-degrees, roughly identical to that seen in optical starlight polarization studies of dark clouds whose evolution is believed to have been dominated by magnetic fields. Second, the mean polarization percentage, 4.6%, is quite high, and two positions show polarization percentages of nearly 8%, the highest yet detected for polarized thermal dust emission. Finally, the polarization of the BN/KL position (2.70% +/- 0.25%) was found to be significantly lower than the polarizations toward positions 30" outside BN/KL.