## Evidence for the importance of resonance scattering in X-ray emission line profiles of the O star $\zeta$~Puppis

Maurice A. Leutenegger$^1}$, Stanley P. Owocki$^2$, Steven M. Kahn$^3$, Frits B. S. Paerels$^1$

1 - Department of Physics and Columbia Astrophysics Laboratory, Columbia University
2 - Bartol Research Institute, University of Delaware
3 - Kavli Institute for Particle Astrophysics and Cosmology, Stanford Linear Accelerator Center and Stanford University

We fit the Doppler profiles of the He-like triplet complexes of \ion{O}{7} and \ion{N}{6} in the X-ray spectrum of the O star $\zeta$ Pup, using XMM-Newton RGS data collected over $\sim 400$ ks of exposure. We find that they cannot be well fit if the resonance and intercombination lines are constrained to have the same profile shape. However, a significantly better fit is achieved with a model incorporating the effects of resonance scattering, which causes the resonance line to become more symmetric than the intercombination line for a given characteristic continuum optical depth $\tau_*$. We discuss the plausibility of this hypothesis, as well as its significance for our understanding of Doppler profiles of X-ray emission lines in O stars.

Reference: ApJ
Status: Manuscript has been submitted