We present adaptive optics spectro-imaging observations of the RW Aur jet in optical forbidden lines , at an angular resolution of 0.4 ^ { \prime \prime } .
Comparison with HST data taken 2 years later shows that proper motions in the blueshifted and redshifted lobes are in the same ratio as their radial velocities , a direct proof that the velocity asymmetry in this jet is real and not an emissivity effect .
The inferred jet inclination to the line of sight is i = 46 \pm 3 ° .
The inner knot spacing appears best explained by time variability with at least two modes : one irregular and asymmetric ( possibly random ) on timescales of \leq 3-10 yr , and another more regular with \simeq 20 yr period .
We also report indirect evidence for correlated velocity and excitation gradients in the redshifted lobe , possibly related to the blue/red velocity and brightness asymmetry in this system .