Gómez-Martín et al., 2024

Astronomical observations of polarized intensity of scattered visible light have revealed the presence of dust envelopes around different types of evolved stars. These observations have helped to determine the diameter and width of dust shells around stars with unprecedented accuracy. Simple geometric particle models are used in order to retrieve dust properties from these observations. In this work we have synthesized and characterized a particulate sample of hydrogenated amorphous carbon (HAC), which is considered to be a realistic carbonaceous interstellar dust analogue based on infrared absorption spectroscopy, and we have measured its phase function and degree of linear polarization at 514 nm using the CODULAB apparatus at IAA-CSIC. The experimental light scattering data has been examined in order to explore possible improvements in the interpretation of astronomical observations of circumstellar dust from the point of view of the retrieval of dust properties, including size, porosity and optical constants. Our results suggest that circumstellar dust observations of polarized intensity attributed to grains with radius ~ 0.1 μm maybe consistent with larger porous aggregates. In addition, an internal 50% wt mixture of HAC and an ultrafine crystalline silicate powder has been generated to study the effect of the mixing of these two components on the light scattering behaviour of dust in circumstellar environments and protoplanetary disks. In this case, the HAC component, which is not very absorbent, has a very small effect and the mixture scatter light similarly to the Forsterite sample.