Orientation of the orbital angular momentum in the observer reference frame. The orbital angular momentum vector ${\widehat{L}}_{\text{f}}$ and a vector pointing from the center of mass of the binary to the ascending node ${\widehat{\mathrm{\Omega }}}_{\text{f}}$ orient the post-explosion orbit of the visible star. Both ${\widehat{L}}_{\text{f}}$ and $\widehat{O}$ are perpendicular to ${\widehat{\mathrm{\Omega }}}_{\text{f}}$, but are not perpendicular to each other. In the particular case shown here ${\widehat{\mathrm{\Omega }}}_{\text{f}}·\widehat{W}>0$, such that ${\mathrm{\Omega }}_{\text{f}}=2\pi -arccos({\widehat{\mathrm{\Omega }}}_{\text{f}}·\widehat{N})$.