Mid-infrared polarimetry and magnetic fields: an observing strategy

Linear polarimetry in the mid-infrared can be used to obtain magnetic field directions in astronomical sources. However, since the polarization can arise from emission and/or absorption from aligned grains, care is needed to plan observations so that enough information is obtained to identify and separate the components of polarization. Procedures for doing this from spectropolarimetry, and from polarimetric imaging at a minimum of two wavebands and making an appropriate filter choice, are presented here, together with an example.