The R Aqr jet was observed with the VLA B-configuration at two epochs
separated by similar to 13.2 yr. Comparison of the resulting 6 cm cont
inuum images show that the radio jet has undergone a lateral countercl
ockwise rotation of -6 degrees-12 degrees on the plane of the sky. The
model of jet parcels on independent trajectories is difficult to reco
ncile with these observations and leads us to consider a path-oriented
jet (i.e., younger parcels follow the same path as older parcels). Co
mparison of the most recent radio image with a nearly contemporaneous
HST/FOC ultraviolet image at similar to 2330 Angstrom suggests that th
e ultraviolet emission lies along the leading side of the rotating rad
io jet. In conjunction with a proper motion analysis of the jet materi
al that yields empirical space-velocity and resulting acceleration-mag
nitude relationships as a function of distance from the central source
, we evaluate the observational results in terms of a schematic model
in which the jet emission consists of plane-parallel isothermal shocks
along the leading edge of rotation. In such a radiating shock, the ul
traviolet-emitting region is consistent with the adiabatic region in t
he form of a high-temperature, low-density sheath that surrounds the c
ooled postshock radio-emitting region. Within the context of the schem
atic model, we obtain the temperatures, densities, and pressures withi
n the preshock, adiabatic, and postshock regions as a function of dist
ance from the central source; the physical parameters so derived compa
re favorably to previously published estimates. We obtain a total jet
mass of 3.1 x 10(-5) M-. and an age of similar to 115 yr. We evaluate
the model in the context of its density-boundary condition, its applic
ability to an episodic or quasi-continuous jet, and angular momentum c
onsiderations.