HD181327 SI,Q_phi and U_phi SPHERE/IRDIS images

We detected the debris disc around HD 181327 in polarised light and total intensity. We measured the scattering phase function and the degree of linear polarisation of the dust at 1.6um in the birth ring. The maximum polarisation is 23.6%+/-2.6% and occurs between a scattering angle of 70{deg} and 82{deg}.

We show that compact spherical particles made of a highly refractive and relatively absorbing material in a differential power-law size distribution of exponent -3.5 can simultaneously reproduce the polarimetric and total intensity scattering properties of the dust. This type of material cannot be obtained with a mixture of silicates, amorphous carbon, water ice, and porosity, and requires a more refracting component such as iron-bearing minerals.

We reveal a striking analogy between the near-infrared polarisation of comets and that of HD 181327. The methodology developed here combining VLT/SPHERE and HST/NICMOS may be applicable in the future to combine the polarimetric capabilities of SPHERE with the sensitivity of JWST.