  We present an analysis of the first observation of the iconic High Mass X-ray
Binary \so with the \chandra High Energy Transmission Gratings during an X-ray
eclipse. The goal of the observation was to study the structure/physical
conditions in the clumpy stellar wind through high resolution spectroscopy. We
find that: a) emission line brightness from K shell transitions, corresponding
to near neutral species, directly correlates with continuum illumination.
However, these lines do not greatly diminish during eclipse. This is readily
explained if fluorescence K$\alpha$ emission comes from the bulk of the wind.
b) The highly ionised Fexxv and Fexxvi Ly$\alpha$ diminish during eclipse.
Thus, they must be produced in the vicinity of the compact object where $\log
\xi >3$. c) to describe the emission line spectrum, the sum of two self
consistent photo ionisation models with low ionisation ($\log \xi\sim -1$) and
high ionisation ($\log \xi\sim 2.4$) is required. From their emission measures,
the clump-to-interclump density ratio can be estimated to be $n_c/n_i\sim 300$.
To fit the complex He-like \ion{Si}{xiii}{} profile, the plasma requires a
broadening with $v_{\rm bulk}\sim 840$ km s$^{-1}$. Reproducing the observed
$r\approx f$ line fluxes requires the addition of a third collisionally ionised
plasma. d) Emission lines widths appear unresolved at the \textsc{hetg}
gratings resolution with exception of Silicon. There is no clear radial
segregation between (quasi)neutral and ionised species, consistent with cold
wind clumps interspersed in a hot rarefied interclump medium.
