Speaker
Description
Understanding dust polarisation at mid-infrared (mid-IR) wavelengths poses difficulties due to its potential dual composition: absorption and emission polarisation. The Aitken technique has been employed to separate the contributions of these two components, in
which the polarisation spectrum is optically thin and the absorption and emission polarisation profiles of the BN object in Orion are
used as a template. Furthermore, the interpretation of the extended polarisation spectrum up to 22 µm is exclusively examined. In
this study, we analyse these mid-IR polarisation spectra using a simple numerical model based on the physics of the radiative torque
(RAT) paradigm, which encompasses both grain alignment and disruption processes. Subsequently, we re-examine a collection of 10
sight lines, with half exhibiting polarisation from 8-22 µm. Our model nicely reproduces these polarisation spectra in a self-consistent
manner. The agreement with the observations at 10 µm is as same as the Aitken method; whereas the predictions of our model for
the 20 µm feature are reasonably good, except at certain sight lines where our model tends to slightly underestimate or overestimate
the observations. In a particular case of Orion/BN, the best model based on the mid-IR observations can account for the emission
polarisation observed in far-IR and sub-millimetre. This study demonstrates the ability of the RAT paradigm to understand mid-IR
polarisation.
Key words. ISM: dust, extinction – ISM: clouds – Infrared: ISM – Submillimeter: ISM – Radiative transfer, Polarisation