X-ray Spectroscopy of the Radiation-Driven Winds of Massive Stars: Line Profile and Line Ratio Diagnostics

TL;DR

This paper discusses how X-ray spectroscopy of massive star winds reveals physical conditions and mass-loss rates through line profile and ratio diagnostics, considering effects like photoelectric absorption and photoexcitation.

Contribution

It introduces models of X-ray line transfer accounting for absorption and excitation effects to better determine wind properties and plasma locations in massive stars.

Findings

X-ray line profiles are significantly affected by photoelectric absorption.

Photoexcitation of helium-like ions helps locate hot plasma regions.

Models improve estimates of stellar wind mass-loss rates.

Abstract

Massive stars drive powerful, supersonic winds via the radiative momentum associated with the thermal UV emission from their photospheres. Shock phenomena are ubiquitous in these winds, heating them to millions, and sometimes tens of millions, of degrees. The emission line spectra from the shock-heated plasma provide powerful diagnostics of the winds' physical conditions, which in turn provide constraints on models of wind shock heating. Here I show how x-ray line transfer is affected by photoelectric absorption in the partially ionized component of the wind and how it can be modeled to determine the astrophysically important mass-loss rates of these stellar winds. I also discuss how photoexcitation out of metastable excited levels of helium-like ions can provide critical information about the location of the hot plasma in magnetically channeled massive star winds.