Smoke on the wind: dust nucleation in archetype colliding wind pinwheel WR104

TL;DR

This study uses 3D hydrodynamic and radiative transfer simulations to investigate dust nucleation in the colliding wind binary WR104, providing insights into dust formation mechanisms and observable features in such systems.

Contribution

It introduces a detailed simulation framework combining hydrodynamics and radiative transfer to analyze dust nucleation in Wolf-Rayet binary systems, linking chemical pathways to observable structures.

Findings

Differential wind speeds influence initial dust velocities.

Constraints on dust nucleation radius depend on dust-to-gas ratio and grain properties.

Dust can escape spiral boundaries due to wind instabilities.

Abstract

A handful of binary Wolf-Rayet stars are known to harbour spectacular spiral structures spanning a few hundred AU. These systems host some of the highest dust production rates in the Universe and are therefore interesting candidates to address the origin of the enigmatic dust excess observed across galactic evolution. The substantial interaction between the winds of the Wolf-Rayet star and its companion constitutes a unique laboratory to study the mechanisms of dust nucleation in a hostile environment. Using the grid-based $\texttt{RAMSES}$ code, we investigate this problem by performing a 3D hydrodynamic simulation of the inner region of the prototypical spiral nebula around WR104. We then process the $\texttt{RAMSES}$ results using the radiative transfer code $\texttt{RADMC3d}$ to generate a candidate observable scene. This allows us to estimate the geometrical parameters of the shocked region. We link those quantities to the specific chemical pathway for dust nucleation, where the hydrogen-rich companion's wind catalyses dust formation. The scaling laws we derive constitute a unique tool that can be directly compared to observations. Depending on the dust nucleation locus, the velocity field reveals a differential wind speed. Thus, the initial dust speed could be more balanced between the speeds of the two stellar winds ($\sim$1600 km/s). With $\texttt{RADMC3d}$, we provide constraints on the dust nucleation radius for different combinations of dust-to-gas ratio, hydrogen enrichment and dust grain properties. Finally, our models reveal that dust may escape beyond the boundaries of the spiral due to hydrodynamical instabilities in the wind collision zone.