X-ray Emission Line Profiles from Wind Clump Bow Shocks in Massive Stars

TL;DR

This paper models X-ray emission line profiles from bow shocks around wind clumps in massive stars, revealing how shock morphology and wind absorption influence observed spectral line shapes.

Contribution

It introduces a self-consistent model of wind clump temperature distribution affecting X-ray line profiles, incorporating bow shock effects for the first time.

Findings

Bow shocks produce double horned line profiles.

Line shapes depend on wind absorption and clump distribution.

Temperature distribution influences X-ray emission features.

Abstract

The consequences of structured flows continue to be a pressing topic in relating spectral data to physical processes occurring in massive star winds. In a preceding paper, our group reported on hydrodynamic simulations of hypersonic flow past a rigid spherical clump to explore the structure of bow shocks that can form around wind clumps. Here we report on profiles of emission lines that arise from such bow shock morphologies. To compute emission line profiles, we adopt a two component flow structure of wind and clumps using two "beta" velocity laws. While individual bow shocks tend to generate double horned emission line profiles, a group of bow shocks can lead to line profiles with a range of shapes with blueshifted peak emission that depends on the degree of X-ray photoabsorption by the interclump wind medium, the number of clump structures in the flow, and the radial distribution of the clumps. Using the two beta law prescription, the theoretical emission measure and temperature distribution throughout the wind can be derived. The emission measure tends to be power law, and the temperature distribution broad in terms of wind velocity. Although restricted to the case of adiabatic cooling, our models highlight the influence of bow shock effects for hot plasma temperature and emission measure distributions in stellar winds and their impact on X-ray line profile shapes. Previous models have focused on geometrical considerations of the clumps and their distribution in the wind. Our results represent the first time that the temperature distribution of wind clump structures are explicitly and self-consistently accounted in modeling X-ray line profile shapes for massive stars.