X-ray spectral diagnostics of activity in massive stars

TL;DR

X-ray spectral analysis of massive stars reveals wind instabilities, shock heating, and provides more accurate mass-loss rates than traditional methods, with implications for understanding stellar wind properties.

Contribution

This paper demonstrates how X-ray spectral diagnostics can accurately measure mass-loss rates and wind characteristics in massive stars, improving upon traditional density-squared diagnostics.

Findings

X-ray line profiles indicate reduced mass-loss rates by factors of 3 to 6.

Broad-band X-ray spectra reveal wind absorption effects.

X-ray diagnostics are less sensitive to clumping than traditional methods.

Abstract

X-rays give direct evidence of instabilities, time-variable structure, and shock heating in the winds of O stars. The observed broad X-ray emission lines provide information about the kinematics of shock-heated wind plasma, enabling us to test wind-shock models. And their shapes provide information about wind absorption, and thus about the wind mass-loss rates. Mass-loss rates determined from X-ray line profiles are not sensitive to density-squared clumping effects, and indicate mass-loss rate reductions of factors of 3 to 6 over traditional diagnostics that suffer from density-squared effects. Broad-band X-ray spectral energy distributions also provide mass-loss rate information via soft X-ray absorption signatures. In some cases, the degree of wind absorption is so high that the hardening of the X-ray SED can be quite significant. We discuss these results as applied to the early O stars zeta Pup (O4 If), 9 Sgr (O4 V((f))), and HD 93129A (O2 If*).