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 is 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.
Neutral (ISM) cross section
Wind cross section models