Carrying a Torch for Dust in Binary Star Systems

TL;DR

This paper models the dust and polarisation in the unusual binary star system Epsilon Sagittarii, revealing that grain sizes around 2 microns can explain the observed high polarisation levels.

Contribution

It presents a spectral energy distribution and radiative transfer model for Epsilon Sagittarii, linking polarimetric measurements to dust grain sizes in the system.

Findings

Polarisation can be explained by dust grains around 2 microns.

The system's high polarisation exceeds infrared excess levels.

Modeling supports the presence of dust grains of specific sizes.

Abstract

Young stars are frequently observed to host circumstellar disks, within which their attendant planetary systems are formed. Scattered light imaging of these proto-planetary disks reveals a rich variety of structures including spirals, gaps and clumps. Self-consistent modelling of both imaging and multi-wavelength photometry enables the best interpretation of the location and size distribution of disks' dust. Epsilon Sagittarii is an unusual star system. It is a binary system with a B9.5III primary that is also believed to host a debris disk in an unstable configuration. Recent polarimetric measurements of the system with the High Precision Polarimetric Instrument (HIPPI) revealed an unexpectedly high fractional linear polarisation, one greater than the fractional infrared excess of the system. Here we develop a spectral energy distribution model for the system and use this as a basis for radiative transfer modelling of its polarisation with the RADMC-3D software package. The measured polarisation can be reproduced for grain sizes around 2.0 microns.