LATERAL SHOCK OF THE R-AQUARII JET

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.