Infrared spectropolarimetric observations of BNKL : the grain alignment mechanism

Spectropolarimetric observations between 8 - 13 μm of BN, IRc 2, 3, 4 and a further region in the Orion infrared complex BNKL are presented. Apart from IRc 2, all show evidence for absorption by aligned grains and have polarization position angles directed at a region close to IRc 2, a property also shared by the self-luminous source IRc 9 at short wavelengths. The evidence strongly suggests that grains are aligned by the intrinsic angular momentum of photons from IRc 2 and it is shown that this is a quantitatively plausible mechanism for the physical conditions in this part of Orion.