Radiation-driven acceleration in the expanding WR140 dust shell

TL;DR

This paper presents multiepoch imagery and geometric modeling of WR140's dust shell, revealing that dust accelerates under radiation pressure, indicating complex physical conditions in colliding-wind binaries.

Contribution

It provides the first detailed kinematic analysis showing dust acceleration in WR140's expanding shell, emphasizing the role of radiation pressure and orbital effects.

Findings

Dust in WR140 accelerates rather than moves at constant speed.

Complex orbital effects create a 'Goldilocks zone' for dust formation.

Radiation pressure significantly influences dust dynamics.

Abstract

The Wolf-Rayet (WR) binary system WR140 is a close (0.9-16.7 mas) binary star consisting of an O5 primary and WC7 companion and is known as the archetype of episodic dust-producing WRs. Dust in WR binaries is known to form in a confined stream originating from the collision of the two stellar winds, with orbital motion of the binary sculpting the large-scale dust structure into arcs as dust is swept radially outwards. It is understood that sensitive conditions required for dust production in WR140 are only met around periastron when the two stars are sufficiently close. Here we present multiepoch imagery of the circumstellar dust shell of WR140. We constructed geometric models that closely trace the expansion of the intricately structured dust plume, showing that complex effects induced by orbital modulation may result in a 'Goldilocks zone' for dust production. We find that the expansion of the dust plume cannot be reproduced under the assumption of a simple uniform-speed outflow, finding instead the dust to be accelerating. This constitutes a direct kinematic record of dust motion under acceleration by radiation pressure and further highlights the complexity of the physical conditions in colliding-wind binaries.