Fast-wind accretion fraction in a circular binary
= Fast-wind accretion fraction in a circular binary
{title2=$\beta_{\rm acc}=G^2M_a^2/(a^2v_w^4)$}
For a fast isotropic cold wind, the <mass density> at a companion at separation $a$ is $(-\dot M_d)/(4\pi a^2v_w)$. The ballistic capture model gives $\dot M_a/(-\dot M_d)=G^2M_a^2/(a^2v_w^4)$. Fast relative to orbital motion also makes the capture radius small compared with the separation.