2025A&A...702A..78M

Context. HD 100453 disk is a prototypical companion-disk interaction system hosting a pair of spirals and a substellar companion.
Aims. We present new noncoronagraphic high-contrast imaging observations of HD 100453 with V filter on SPHERE/ZIMPOL. We aim to accurately measure the reflected polarized intensity, the disk intensity, and the degree of polarization at multiwavelength; characterize the dust properties in the disk ring and the companion-driven spiral arms; and search for the radial dependencies of dust scattering properties within the disk.
Methods. We combined high-contrast imaging data of the reflected light from 0.55 to 2.2 μm using the V, I', J, and Ks band data of ZIMPOL and IRDIS at VLT/SPHERE. For each observational epoch, we corrected for the smearing effect to derive the intrinsic disk-integrated polarized flux. We applied reference differential imaging to extract the disk intensity for the V and Ks bands using star hopping observations. We then used RADMC-3D radiative transfer modeling with a parametrized Henyey-Greenstein phase function to constrain the dust properties.
Results. For the integrated intrinsic polarized flux of the disk, we derived a steady increase with wavelengths from ${\hat Q_\varphi }/{I_ \star }\left( V \right) = 0.3\% $ to ${\hat Q_\varphi }/{I_ \star }\left( K \right) = 1.2\% $. We obtained the first V-band total intensity for HD 100453 with ZIMPOL star hopping. The integrated total flux I_disk/I_★(V) = 1.5% increases to I_disk/I_★(K) = 4.8%. Both the total intensity and the polarization fraction show red colors, and the intrinsic maximum degree of polarization increases moderately from 40% to 55%. From the V to Ks band, the dominating dust in the outer disk has an increasing scattering albedo and degree of polarization, while the asymmetry parameter slightly decreases. The outer disk of HD 100453 contains sub-micron-sized low porosity grains/aggregates. The cavity in scattered light is not empty and is replenished with optically thin dust with a maximum size of ≤ 0.1 μm. The linear polarization is higher in the spiral region than in the other regions, suggesting different dust properties in those regions.