Simulating stellar winds in AMUSE

Abstract

Aims. We present STELLAR_WIND.PY, a module that provides multiple methods of simulating stellar winds using smoothed particle hydrodynamics codes (SPH) within the astrophysical multipurpose software environment (AMUSE) framework. Methods. The module currently includes three ways of simulating stellar winds: With the simple wind mode, we create SPH wind particles in a spherically symmetric shell for which the inner boundary is located at the radius of the star. We inject the wind particles with a velocity equal to their terminal velocity. The accelerating wind mode is similar, but with this method particles can be injected with a lower initial velocity than the terminal velocity and they are accelerated away from the star according to an acceleration function. With the heating wind mode, SPH particles are created with zero initial velocity with respect to the star, but instead wind particles are given an internal energy based on the integrated mechanical luminosity of the star. This mode is designed to be used on longer timescales and larger spatial scales compared to the other two modes and assumes that the star is embedded in a gas cloud. Results. We present a number of tests and compare the results and performance of the different methods. For fast winds, we find that both the simple and accelerating mode can reproduce the desired velocity, density and temperature profiles. For slow winds, the simple wind mode is insufficient due to dominant hydrodynamical effects that change the wind velocities. The accelerating mode, with additional options to account for these hydrodynamical effects, can still reproduce the desired wind profiles. We test the heating mode by simulating both a normal wind and a supernova explosion of a single star in a uniform density medium. The stellar wind simulation results matches the analytical solution for an expanding wind bubble. The supernova simulation gives qualitatively correct results, but the simulated bubble expands faster than the analytical solution predicts. We conclude with an example of a triple star system which includes the colliding winds of all three stars.