# Variability in X-ray line ratios in helium-like ions of massive stars: the wind-driven case

## TL;DR

This paper investigates how variability in stellar wind properties, specifically mass loss, affects the X-ray line ratios in helium-like ions of massive stars, providing insights into the plasma's proximity to the star.

## Contribution

It explores the impact of wind-driven variability on X-ray line ratio diagnostics, highlighting potential biases in measuring plasma location in massive star winds.

## Key findings

- Variable mass loss can significantly modulate the f/i ratio.
- Wind variability may bias measurements of plasma proximity.
- Line ratio variability offers new diagnostic potential.

## Abstract

High spectral resolution and long exposure times are providing unprecedented levels of data quality of massive stars at X-ray wavelengths. A key diagnostic of the X-ray emitting plasma are the fir lines for He-like triplets. In particular, owing to radiative pumping effects, the forbidden-to-intercombination line luminosity ratio, R=f/i, can be used to determine the proximity of the hot plasma to the UV-bright photospheres of massive stars. Moreover, the era of large observing programs additionally allows for investigation of line variability. This contribution is the second to explore how variability in the line ratio can provide new diagnostic information about distributed X-rays in a massive star wind. While there are many ways to drive variability in the line ratio, we use variable mass loss as an illustrative example. The f/i ratio can be significantly modulated owing to evolving wind properties. We evaluate how variable mass loss might bias measures of f/i.