implies that $90^{\circ} -i< \phi_a$, such that our line of sight toward the shocked secondary wind would go through the undisturbed secondary wind. The column density through this low density gas is very low. Instead, we suggest that the secondary star resides on the far side during apastron, and the column density includes the undisturbed primary wind as well as the shocked primary wind.

To calculate the column density for our preferred orientation of $\omega=90^\circ$, we follow KS08 and use the geometry as drawn schematically in Fig. \[fig:NHgeo\]. The contact discontinuity shape is approximated by an hyperboloid at a distance $D_{g2}\simeq0.3 r$ from the secondary at the stagnation point (the stagnation point is the point where the two winds’ momenta balance each other).

Our model of the primary wind includes a weak pre-shock magnetic field. In the post shock region the gas is highly compressed, and the magnetic field becomes dominant. The magnetic pressure limits the compression of the postshocked primary wind. The uncertainties in the intensity and geometry of the magnetic field introduce large uncertainties (Kashi & Soker 2007a). The magnetic field role is parameterized by the compression factor $\eta_B$ which is the ratio between the pre-shock magnetic and 