$(i, \omega)=(42^\circ, 90^\circ)$, and found the resulted flux at phase $0.98$ to be $\sim 5$ times below the observed one (Parkin, R., private communication 2009). However, there are problems with their calculation. First, P09 assume the emission measure to increase as $EM\propto r^{-1}$, where $r$ is the orbital separation. However, the increase in the emission measure is smaller. For example, at phase $0.99$ the orbital separation is $16$ times smaller than at apastron, but the emission measure is only $\sim 7$ times larger than the apastron value (H07). In addition, before periastron the two stars approach each other, an effect that increases the X-ray emission for constant wind properties, e.g., by $\sim 30 \% $ at phase $0.98$ (A06); this effect was not considered by P09.

The conclusion is that the secondary wind starts being disturbed weeks before periastron, and the emission measure does not increase as much as assumed by P09. To explain the observed flux, the column density cannot increase by the large factor predicted by the $\omega\simeq 270 ^\circ$ periastron longitude. A shallower increase in the column density is reproduced by our preferred periastron longitude $\omega = 90 ^\circ$.

We can summarize this section by stating that 