Evidence for the importance of resonance scattering in X-ray emission line profiles of the O star ζ Puppis
Abstract
We fit the Doppler profiles of the He-like triplet complexes of O7 and N6 in the X-ray spectrum of the O star ζ Puppis, using XMM-Newton RGS data collected over 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.
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