Binary period invariant for a constant wind angular-momentum factor ($P_{\mathrm{orb}}{M}_1^3{M}_2^3/(M_1+M_2{)}^{3\lambda +1}=\mathrm{constant}$)

If an escaping stellar wind carries specific orbital angular momentum $\lambda J/M$ with constant $\lambda$, then $\dot{J}/J=\lambda \dot{M}/M$ and $J\propto M^{\lambda }$. Combining this with circular-binary orbital angular momentum gives the displayed period invariant. It is a different prescription from donor-wind angular-momentum loss, whose specific angular momentum generally varies with mass ratio.