= Binary period invariant for a constant wind angular-momentum factor
{title2=$P_{\rm orb}M_1^3M_2^3/(M_1+M_2)^{3\lambda+1}=\mathrm{constant}$}
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.
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