Evidence for precession of the R Aquarii jet

Several models of the R Aqr northeast jet have been proposed which attempt to explain the presence of shock excitation, resulting in a confusing picture of this nearest astrophysical jet. This paper compares observations of the jet in the R Aqr system with the HST's Faint Object Camera (FOC) and radio continuum images acquired with the VLA. The forbidden-O III jet structure is derived from restored FOC imagery, which has been convolved with an elliptical Gaussian of the same size as the restoring beam of the 6-cm VLA maps, allowing image comparison at the same spatial resolution. It is found that, at increasing distances from the central star, the forbidden O III emission knots that comprise the optical jet occur at systematically larger position angles when compared with corresponding features in the radio images. The angular separation of forbidden O III and radio continuum emission can be understood in terms of a shock formed when ejecta in the stream interacts with previously existing circumstellar material and subsequently cools by nebular line emission.