The scattering properties of the dust originating from debris discs are still poorly known. The analysis of scattered light is however a powerful remote-sensing tool to understand the physical properties of dust particles orbiting other stars. Scattered light is indeed widely used to characterise the properties of cometary dust in the solar system. We aim to measure the morphology and scattering properties of the dust from the debris ring around HR4796A in polarised optical light. We obtained high-contrast polarimetric images of HR4796A in the wavelength range 600-900nm with the SPHERE / ZIMPOL instrument on the Very Large Telescope. We measured for the first time the polarised phase function of the dust in a debris system over a wide range of scattering angles in the optical. We confirm that it is incompatible with dust particles being compact spheres under the assumption of the Mie theory, and propose alternative scenarios compatible with the observations, such as particles with irregular surface roughness or aggregate particles.
@article{arxiv.1905.03603,
title = {Optical polarized phase function of the HR\,4796A dust ring},
author = {J. Milli and N. Engler and H. M. Schmid and J. Olofsson and F. Menard and Q. Kral and A. Boccaletti and P. Thebault and E. Choquet and D. Mouillet and A. -M. Lagrange and J. C. Augereau and C. Pinte and G. Chauvin and C. Dominik and C. Perrot and A. Zurlo and T. Henning and M. Min and J. L. Beuzit and H. Avenhaus and A. Bazzon and T. Moulin and M. Llored and O. Moeller-Nilsson and R. Roelfsema and J. Pragt},
journal= {arXiv preprint arXiv:1905.03603},
year = {2019}
}