Evidence for the importance of resonance scattering in X-ray emission line profiles of the O star $ζ$ Puppis

Leutenegger, Maurice A.; Owocki, Stanley P.; Kahn, Steven M.; Paerels, Frits B. S.

Evidence for the importance of resonance scattering in X-ray emission line profiles of the O star $ζ$ Puppis

Authors

Leutenegger, Maurice A.

Owocki, Stanley P.

Kahn, Steven M.

Paerels, Frits B. S.

Description

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 $ζ$ Puppis, 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 $τ_*$. 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.
29 pages, 8 figures, revised version accepted by ApJ