# Radiation-driven acceleration in the expanding WR140 dust shell

**Authors:** Yinuo Han, Peter G. Tuthill, Ryan M. Lau, Anthony Soulain  
**arXiv:** [2210.06556](https://arxiv.org/abs/2210.06556)  
**Date:** 2022-10-12  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2210.06556v1/

## Key points

- WR140 is a well-known archetype of episodic dust-producing WRs
- It consists of a close binary star with an O5 primary and WC7 companion
- Dust forms in a confined stream originating from the collision of the two stellar winds
- Sensitive conditions required for dust production in WR140 are only met around periastron when the two stars are sufficiently close
- Multiepoch imagery shows that complex effects induced by orbital modulation may result in a 'Goldilocks zone' for dust production
- Geometric models have been constructed to reproduce structural features, but not all predicted features are apparent in the data
- Radiation-driven acceleration plays an important role in shaping intricate structures, highlighting further complexity in colliding-wind binaries' physical conditions.

## Summary

The Wolf-Rayet (WR) binary system WR140 is a well-known archetype of episodic dust-producing WRs. It consists of a close binary star with an O5 primary and WC7 companion, where dust forms in a confined stream originating from the collision of the two stellar winds. The orbital motion of the binary sculpts the large-scale dust structure into arcs as it is swept radially outwards. Sensitive conditions required for dust production in WR140 are only met around periastron when the two stars are sufficiently close. Recently, multiepoch imagery of the circumstellar dust shell of WR140 has been presented, which shows that complex effects induced by orbital modulation may result in a 'Goldilocks zone' for dust production. Geometric models have been constructed that closely trace the expansion of the intricately structured dust plume, revealing that not all predicted features are apparent in the data. Although primarily designed to reproduce structural features, its physical interpretation implies a pinwheel system producing isothermal, optically thin dust at a constant rate. However, there is a clear absence of structures predicted by the geometric model, most noticeably dust features to the north and west (an outer-western arc) and below the southern bar. Further analysis reveals that this cannot be explained by simple density variations due to radiation pressure or wind collisions alone. Instead, it suggests that radiation-driven acceleration plays an important role in shaping these intricate structures. The expansion of the dust plume cannot be reproduced under the assumption of a simple uniform-speed outflow; instead, it appears that radiation pressure accelerates the dust particles directly. This constitutes a direct kinematic record of dust motion under acceleration by radiation pressure and highlights further complexity in colliding-wind binaries' physical conditions. Overall, this study provides new insights into how complex interactions between stellar winds and radiation can shape dusty environments around massive stars such as those found in WR binaries like WR140.