The complex dependencies of Wolf-Rayet winds -- Insights from detailed radiative transfer models

TL;DR

This paper reviews recent advances in modeling Wolf-Rayet star winds using detailed radiative transfer and hydrodynamics, highlighting complex dependencies and future challenges in understanding their mass loss mechanisms.

Contribution

It introduces new insights from 1D and upcoming 2D/3D models, revealing complex wind dependencies and extending understanding to various WR star types.

Findings

Identified new scalings of WR wind properties with stellar parameters.

Uncovered dependencies of later-type and hydrogen-containing WR stars.

Discussed future integration of multi-dimensional simulations into models.

Abstract

With their emission-line dominated spectra, the appearance of Wolf-Rayet stars is shaped by their strong stellar winds. Yet, the physical mechanisms behind their high mass loss have long remained enigmatic. While we know nowadays that radiative driving is sufficient to explain WR-type outflows, a coherent description of them is still lacking, not least to the complex physical conditions invalidating some of the approximations sufficient for other hot-star winds. One promising instrument towards a better understanding of WR winds are comoving-frame, non-LTE stellar atmosphere models including a consistent solution of the hydrodynamics. While so far limited to 1D, their detailed treatment of the radiative transfer and the population numbers is key to overcome the traditional problem of connecting stellar structure models with observed spectra. By creating larger model sequences, we can identify previously unknown scalings and describe trends of WR wind quantities with fundamental stellar parameters and abundances. This article will present a summary of recent insights on WR-type winds, revealing a complex picture with various remaining challenges. Beside covering classical, hydrogen-free WR stars, we present new results to uncover dependencies of later-type WR stars and the presence of hydrogen-containing envelopes. We further discuss oncoming challenges and insights from 2D and 3D RHD simulations which need to be mapped into 1D dynamical atmosphere models.