Even in these instability shock models, most of the wind is cold and is a source of X-ray continuum opacity
The massive winds of O stars are expected to be optically thick to soft X-raysÉthe inner tens of R* may be heavily absorbed: or so it was thought.

The wavelength dependence of individual lines leads to the expectation that different absorption characteristics will be seen in different lines from a given star.
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Neutral (ISM) cross section
Wind cross section models