Constraints on porosity and mass loss in O-star winds from modeling of X-ray
emission line profile shapes

Maurice A. Leutenegger$^{1,2}$, David H. Cohen$^3$, Jon O. Sundqvist$^{4,5}$, Stanley P. Owocki$^4$

1 - CRESST and X-ray Astrophysics Laboratory
NASA/Goddard Space Flight Center;
2 - Department of Physics, University of Maryland, Baltimore County;
3 - Department of Physics and Astronomy, Swarthmore College;
4 - Bartol Research Institute, University of Delaware;
5 - Universitaetssternwarte Muenchen

We fit X-ray emission line profiles in high resolution XMM-Newton and Chandra grating spectra of the early O supergiant Zeta Pup with models that include the effects of porosity in the stellar wind. We explore the effects of porosity due to both spherical and flattened clumps. We find that porosity models with flattened clumps oriented parallel to the photosphere provide poor fits to observed line shapes. However, porosity models with isotropic clumps can provide acceptable fits to observed line shapes, but only if the porosity effect is moderate. We quantify the degeneracy between porosity effects from isotropic clumps and the mass-loss rate inferred from the X-ray line shapes, and we show that only modest increases in the mass-loss rate (<~ 40%) are allowed if moderate porosity effects (h_infty <~ R_*) are assumed to be important. Large porosity lengths, and thus strong porosity effects, are ruled out regardless of assumptions about clump shape. Thus, X-ray mass-loss rate estimates are relatively insensitive to both optically thin and optically thick clumping. This supports the use of X-ray spectroscopy as a mass-loss rate calibration for bright, nearby O stars.

Reference: 2013 ApJ, 770, 80
Status: Manuscript has been accepted


Comments: Preprint available at