Structure of the interaction between a wind and a homologous ejecta with ρ ∝ r⁻² from a computation using PLUTO with an isothermal equation of state. The left panels show the density and the velocity of the material. The right panels zoom in on the internal shock structure at the interface between the wind and the ejecta. Another shock structure appears at the interface between the ejecta and the ISM at r ≈ 1.6 AU.