Constraints on Porosity and Mass Loss in O-star Winds from Modeling of X-ray Emission Line Profile Shapes
Abstract
Spectrally resolved X-ray line shapes in massive stars provide important diagnostics of X-ray production mechanisms and they have also, surprisingly, been used to make some of the most accurate and model-independent wind mass-loss rate estimates. Measurements of several nearby O stars using the grating spectrometers onboard {\it Chandra} and XMM-{\it Newton} have revised downward the mass-loss rates of O stars, with implications for stellar evolution and the energy budget in clusters. But if these winds are porous, then the X-ray mass-loss rates might be subject to systematic underestimates. Here we present a formalism for modeling the effects of wind porosity on X-ray emission line profiles, and fit these models to Chandra and XMM observations of $\zeta$ Pup. We find that strong porosity effects are ruled out, and for moderate porosity we quantify the degeneracy between assumed porosity length and derived mass-loss rate. We conclude that mass-loss rates derived from fitting X-ray line profiles assuming no porosity effects are overestimated by at most 50\% if moderate porosity effects are indeed important.
- Publication:
-
AAS/High Energy Astrophysics Division #13
- Pub Date:
- April 2013
- Bibcode:
- 2013HEAD...1312501L