= Stellar asymmetric drift
{title2=$v_a=v_c-\overline v_\phi$}
= Asymmetric drift
{synonym}
{wiki}
<Stellar asymmetric drift> is the lag of a pressure-supported <stellar population>'s mean rotation behind the local <circular speed>. Neglecting the tilted <velocity ellipsoid>, radial <Jeans equation> balance gives
$$
v_c^2-\overline v_\phi^2=\sigma_R^2\left[-\frac{d\log(n\sigma_R^2)}{d\log R}-1+\frac{\sigma_\phi^2}{\sigma_R^2}\right].
$$
A declining density and larger random velocities generally increase the lag; gravitational balance is supplied partly by random-motion stresses.
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