Quantitative analysis of resolved X-ray emission line profiles of O stars

TL;DR

This study uses X-ray spectral data of ζ Pup to compare wind models with different mass-loss rates and porosity, finding that lower mass-loss rates fit data without porosity, while high mass-loss rates require unrealistic porosity lengths.

Contribution

It demonstrates that simple non-porous wind models with reduced mass-loss rates can fit X-ray data, challenging the necessity of extreme wind porosity in stellar wind modeling.

Findings

Lower mass-loss rate models fit the data well.

High mass-loss rate models require extreme porosity lengths.

Large porosity lengths are inconsistent with wind simulations.

Abstract

By quantitatively fitting simple emission line profile models that include both atomic opacity and porosity to the Chandra X-ray spectrum of $\zeta$ Pup, we are able to explore the trade-offs between reduced mass-loss rates and wind porosity. We find that reducing the mass-loss rate of $\zeta$ Pup by roughly a factor of four, to 1.5 \times 10^{-6} M_sun/yr, enables simple non-porous wind models to provide good fits to the data. If, on the other hand, we take the literature mass-loss rate of 6 \times 10^{-6} M_sun/yr, then to produce X-ray line profiles that fit the data, extreme porosity lengths -- of $h_{\infty} \approx 3$ Rstar -- are required. Moreover, these porous models do not provide better fits to the data than the non-porous, low optical depth models. Additionally, such huge porosity lengths do not seem realistic in light of 2-D numerical simulations of the wind instability.