X-ray emission from hydrodynamical simulations in non-LTE wind models

TL;DR

This paper develops an analytical approximation for X-ray emission in hot star winds based on hydrodynamical simulations, improving the accuracy of non-LTE wind models and better matching observed ionization and luminosity relations.

Contribution

It introduces a new analytical approximation derived from hydrodynamical simulations to incorporate X-ray emission into non-LTE wind models.

Findings

Improved agreement between model ionization fractions and observations.

Better match of the L_x-L relation slope with observations.

X-ray luminosity is still underestimated by a factor of three.

Abstract

Hot stars are sources of X-ray emission originating in their winds. Although hydrodynamical simulations that are able to predict this X-ray emission are available, the inclusion of X-rays in stationary wind models is usually based on simplifying approximations. To improve this, we use results from time-dependent hydrodynamical simulations of the line-driven wind instability (seeded by the base perturbation) to derive the analytical approximation of X-ray emission in the stellar wind. We use this approximation in our non-LTE wind models and find that an improved inclusion of X-rays leads to a better agreement between model ionization fractions and those derived from servations. Furthermore, the slope of the L_x-L relation is in better agreement with observations, however the X-ray luminosity is underestimated by a factor of three. We propose a possible solution for this discrepancy.