Stellar wind in state transitions of high-mass X-ray binaries

TL;DR

This paper introduces a new 3D hydrodynamic simulation code to study stellar winds in high-mass X-ray binaries, revealing how forces like Coriolis and X-ray ionization affect wind structure and variability.

Contribution

The paper presents a novel 3D time-dependent radiative hydrodynamics code that models stellar wind interactions in binaries, incorporating multiple physical effects for the first time.

Findings

Coriolis force significantly affects mass loss and accretion.

Gravitational focusing creates a cone-shaped gaseous tail.

X-ray photo-ionization impacts wind structure and variability.

Abstract

Aims: We have developed a new code for the three-dimensional time-dependent raditation hydrodynamic simulation of the stellar wind in interacting binaries to improve models of accretion in high-mass X-ray binaries and to quantitatively clarify the observed variability of these objects. We used the code to test the influence of various parameters on the structure and properties of circumstellar matter. Methods: Our code takes into account acceleration of the wind due to the Roche effective potential, Coriolis force, gas pressure, and (CAK-) radiative pressure in the lines and continuum of the supergiant radiation field that is modulated by its gravity darkening and by the photo-ionization caused by X-ray radiation from the compact companion. The parameters of Cygnus X-1 were used to test the properties of our model. Results: Both two- and three-dimensional numerical simulations show that the Coriolis force substantially influences the mass loss and consequently the accretion rate onto the compact companion. The gravitational field of the compact companion focuses the stellar wind, which leads to the formation of a curved cone-like gaseous tail behind the companion. The changes of X-ray photo-ionization of the wind material during X-ray spectral-state transitions significantly influence the wind structure and offer an explanation of the variability of Cygnus X-1 in optical observations (the H$\alpha$ emission).