S. Mohamed, J. Mackey, N. Langer, Ph. Podsiadlowski

• Wolf-Rayet (WR) stars lose copious amounts of mass and momentum through dense stellar winds. The interaction of these outflows with their surroundings results in highly structured and complex circumstellar environments, often featuring knots, arcs, shells and spirals. Recent improvements in computational power and techniques have led to the development of detailed, multi-dimensional simulations that have given new insight into the origin of these structures, and better understanding of the physical mechanisms driving their formation. We review three of the main mechanisms that shape the outflows of WR stars: • interaction with the interstellar medium (ISM), i.e., wind-ISM interactions; • interaction with a stellar wind, either from a previous phase of evolution or the wind from a companion star, i.e., wind-wind interactions; • and interaction with a companion star that has a weak or insignificant outflow (e.g., a compact companion such as a neutron star or black hole), i.e.,wind-companion interactions. We also highlight theWolf-Rayet (WR) stars lose copious amounts of mass and momentum through dense stellar winds. The interaction of these outflows with their surroundings results in highly structured and complex circumstellar environments, often featuring knots, arcs, shells and spirals. Recent improvements in computational power and techniques have led to the development of detailed, multi-dimensional simulations that have given new insight into the origin of these structures, and better understanding of the physical mechanisms driving their formation. We review three of the main mechanisms that shape the outflows of WR stars: • interaction with the interstellar medium (ISM), i.e., wind-ISM interactions; • interaction with a stellar wind, either from a previous phase of evolution or the wind from a companion star, i.e., wind-wind interactions; • and interaction with a companion star that has a weak or insignificant outflow (e.g., a compact companion such as a neutron star or black hole), i.e.,wind-companion interactions. We also highlight the broader implications and impact of these circumstellar structures for related phenomena, e.g., for X-ray binaries and Gamma-ray bursts.…