2025MNRAS.540..973C

The wind ejection velocity of a star in orbital motion in a binary system undergoes a variation along its orbit with respect to the centre of mass. Due to this time-dependent ejection velocity, the wind collides with itself, generating two-shock wave structures called working surfaces, which propagate outwards in the flow. In this work, we present both an analytic model and one-dimensional numerical simulations to describe the formation and dynamical evolution of the working surfaces, assuming an elliptic orbit for the star. In addition, the luminosity emitted by these structures, as they move away from the source, is computed. Our semi-analytic model of internal shock dynamics and numerical simulations show that two working surfaces are formed for directions near the periastron (in the range of ${\pm} 60^{\circ }$), which propagate with different velocities, where the faster one is produced later. These two working surfaces collide with each other, producing a single working surface. We found a good agreement between our analytic model and our numerical simulations.