Colliding Stellar Wind Models with Nonequilibrium Ionization: X-rays from WR 147

TL;DR

This study introduces a nonequilibrium ionization model for colliding stellar winds in massive binaries, successfully fitting WR 147's X-ray spectra and suggesting collisionless shocks with adjusted stellar wind parameters.

Contribution

The paper presents a novel numerical model incorporating nonequilibrium ionization effects in colliding stellar wind simulations, improving spectral fits for WR 147.

Findings

Model reproduces observed X-ray spectra accurately.

Stellar wind velocities need to be increased by 1.4-1.6 times.

Mass loss rates should be reduced by about half.

Abstract

The effects of nonequilibrium ionization are explicitly taken into account in a numerical model which describes colliding stellar winds (CSW) in massive binary sytems. This new model is used to analyze the most recent X-ray spectra of the WR+OB binary system WR 147. The basic result is that it can adequately reproduce the observed X-ray emission (spectral shape, observed flux) but some adjustment in the stellar wind parameters is required. Namely, (i) the stellar wind velocities must be higher by a factor of 1.4 - 1.6; (ii) the mass loss must be reduced by a factor of ~ 2. The reduction factor for the mass loss is well within the uncertainties for this parameter in massive stars, but given the fact that the orbital parameters (e.g., inclination angle and eccentricity) are not well constrained for WR 147, even smaller corrections to the mass loss might be sufficient. Only CSW models with nonequilibrium ionization and equal (or nearly equal) electron and ion postshock temperature are successful. Therefore, the analysis of the X-ray spectra of WR 147 provides evidence that the CSW shocks in this object must be collisionless.