Polarization of the λ = 1.3 millimeter continuum radiation from the Kleinmann-low nebula

We have detected linear polarization in the 1.3 mm continuum emission from the Kleinmann-Low (KL) nebula in Orion. The result is P = (2.6 ± 0.8)% and Φ = 40° ± 8°. The polarization is due to thermal emission from magnetically aligned dust grains. Our measurement is of higher spatial resolution than polarization measurements of this source which have been made at far-infrared wavelengths, and the magnetic field direction which we infer from our result differs by about 20° from that which has been inferred from the far-infrared results. The difference is probably due to structure in the magnetic field lines within the region sampled by the far-infrared observations. The field direction given by the 1.3 mm result is parallel to the axis of the highvelocity bipolar outflow in KL. In principle, the difference between the far-infrared and 1.3 mm results could be due to Faraday rotation in the Orion A H II region, which lies in front of KL. However, the required line-of-sight magnetic field is 300 μG, which seems too high. Faraday rotation should be observable at wavelengths near 3 mm, providing a method for estimating magnetic field strengths in the Orion A H II region.