  Archival X-ray spectra of the four prominent single, non-magnetic O stars
Zeta Pup, Zeta Ori, Ksi Per and Zeta Oph, obtained in high resolution with
Chandra HETGS/MEG have been studied. The resolved X-ray emission line profiles
provide information about the shocked, hot gas which emits the X-radiation, and
about the bulk of comparably cool stellar wind material which partly absorbs
this radiation. In this paper, we synthesize X-ray line profiles with a model
of a clumpy stellar wind. We find that the geometrical shape of the wind
inhomogeneities is important: better agreement with the observations can be
achieved with radially compressed clumps than with spherical clumps. The
parameters of the model, i.e. chemical abundances, stellar radius, mass-loss
rate and terminal wind velocity, are taken from existing analyses of UV and
optical spectra of the programme stars. On this basis, we also calculate the
continuum-absorption coefficient of the cool-wind material, using the Potsdam
Wolf-Rayet (PoWR) model atmosphere code. The radial location of X-ray emitting
gas is restricted from analysing the fir line ratios of helium-like ions. The
only remaining free parameter of our model is the typical distance between the
clumps; here, we assume that at any point in the wind there is one clump
passing by per one dynamical time-scale of the wind. The total emission in a
model line is scaled to the observation. There is a good agreement between
synthetic and observed line profiles. We conclude that the X-ray emission line
profiles in O stars can be explained by hot plasma embedded in a cool wind
which is highly clumped in the form of radially compressed shell fragments.
