%APattle, Kate%ALai, Shih-Ping%AWright, Melvyn%ACoudé, Simon%APlambeck, Richard%AHoang, Thiem%ATang, Ya-Wen%ABastien, Pierre%AEswaraiah, Chakali%AFuruya, Ray%AHwang, Jihye%AInutsuka, Shu-ichiro%AKim, Kee-Tae%AKirchschlager, Florian%AKwon, Woojin%ALee, Chang%ALiu, Sheng-Yuan%ALyo, Aran%AOhashi, Nagayoshi%ARawlings, Mark%ATahani, Mehrnoosh%ATamura, Motohide%ASoam, Archana%AWang, Jia-Wei%AWard-Thompson, Derek%BJournal Name: Monthly Notices of the Royal Astronomical Society; Journal Volume: 503; Journal Issue: 3 %D2021%I %JJournal Name: Monthly Notices of the Royal Astronomical Society; Journal Volume: 503; Journal Issue: 3 %K %MOSTI ID: 10388653 %PMedium: X %TOMC-1 dust polarization in ALMA Band 7: diagnosing grain alignment mechanisms in the vicinity of Orion Source I %XABSTRACT We present ALMA Band 7 polarization observations of the OMC-1 region of the Orion molecular cloud. We find that the polarization pattern observed in the region is likely to have been significantly altered by the radiation field of the >104 L⊙ high-mass protostar Orion Source I. In the protostar’s optically thick disc, polarization is likely to arise from dust self-scattering. In material to the south of Source I – previously identified as a region of ‘anomalous’ polarization emission – we observe a polarization geometry concentric around Source I. We demonstrate that Source I’s extreme luminosity may be sufficient to make the radiative precession time-scale shorter than the Larmor time-scale for moderately large grains ($\gt 0.005\!-\!0.1\, \mu$m), causing them to precess around the radiation anisotropy vector (k-RATs) rather than the magnetic field direction (B-RATs). This requires relatively unobscured emission from Source I, supporting the hypothesis that emission in this region arises from the cavity wall of the Source I outflow. This is one of the first times that evidence for k-RAT alignment has been found outside of a protostellar disc or AGB star envelope. Alternatively, the grains may remain aligned by B-RATs and trace gas infall on to the Main Ridge. Elsewhere, we largely find the magnetic field geometry to be radial around the BN/KL explosion centre, consistent with previous observations. However, in the Main Ridge, the magnetic field geometry appears to remain consistent with the larger-scale magnetic field, perhaps indicative of the ability of the dense Ridge to resist disruption by the BN/KL explosion. %0Journal Article