Radiative transfer on decretion discs of Be binaries

TL;DR

This paper investigates how binarity influences the structure and variability of Be star decretion discs using SPH simulations and non-LTE radiative transfer calculations, revealing phase-locked disc features and azimuthal dependencies.

Contribution

It combines hydrodynamic simulations with detailed radiative transfer modeling to analyze the impact of binary companions on Be star discs, a novel integrated approach.

Findings

Disc structure is locked to orbital phase.

Disc exhibits azimuthal angle dependence.

First detailed non-LTE radiative transfer results for Be binary discs.

Abstract

In this work we explore the effect of binarity in the decretion disc of Be stars, in order to explain their variability. To this aim, we performed smoothed particle hydrodynamics (SPH) simulations on Be binary systems, following the matter ejected isotropically from the equator of the Be star towards the base of an isothermal decretion disc. We let the system evolve for time long enough to be considered at steady state, and focus on the effect of viscosity for coplanar prograde binary orbits. The disc structure is found to be locked to the orbital phase, exhibiting also a dependence on the azimuthal angle. Additionally, we present the first results from detailed non-local thermodynamic equilibrium (non-LTE) radiative transfer calculations of the disc structure computed with the SPH code. This is achieved by the use of the three-dimensional (3D) Monte Carlo code HDUST, which can produce predictions with respect to a series of observables.