Linearization at L2
= Linearization at L2
{title2=$B=\mu_1/r_1^3+\mu_2/r_2^3$}
In unit binary separation and mean motion, displacements obey $\ddot X-2\dot Y=(1+2B)X$ and $\ddot Y+2\dot X=(1-B)Y$, where $B=\mu_1/r_1^3+\mu_2/r_2^3$ at $L_2$. The characteristic polynomial is $\lambda^4+(2-B)\lambda^2+(1+2B)(1-B)$. The small-secondary limit has $B\to4$.