# Effect of dust size and structure on scattered light images of protoplanetary discs

## TL;DR

This study uses radiative transfer simulations to explore how dust size and structure influence the scattered light and polarization in protoplanetary discs, providing insights into dust properties from observations.

## Contribution

It demonstrates that polarization fraction and scattered light colors can reveal dust aggregate porosity, size, and structure in protoplanetary discs.

## Key findings

- Highly porous dust aggregates produce high polarization fractions.
- Dust color variations from blue to red depend on fractal dimension and monomer size.
- Discs with grey or blue colors and high polarization likely contain large porous dust aggregates.

## Abstract

We study scattered light properties of protoplanetary discs at near-infrared wavelengths for various dust size and structure by performing radiative transfer simulations. We show that different dust structures might be probed by measuring disk polarisation fraction as long as the dust radius is larger than the wavelength. When the radius is larger than the wavelength, disc scattered light will be highly polarised for highly porous dust aggregates, whereas more compact dust structure tends to show low polarisation fraction. Next, roles of monomer radius and fractal dimension for scattered light colours are studied. We find that, outside the Rayleigh regime, as fractal dimension or monomer radius increases, colours of the effective albedo at near-infrared wavelengths vary from blue to red. Our results imply that discs showing grey or slightly blue colours and high polarisation fraction in near-infrared wavelengths might be explained by the presence of large porous aggregates containing sub-microns sized monomers.