Three-dimensional motion in the radio jet of the binary system R Aquarii

Abstract

R AQUARII is a symbiotic binary system surrounded by a complex extended optical nebulosity¹. At radio and optical wavelengths a jet is seen to emerge from the central binary system^2,3. We have observed R Aqr using the Very Large Array. Comparison with earlier radio observations shows that five out of six bright components in the radio jet have moved. One radio component has the same proper motion as the optical Mira, the primary star of the binary. At a distance of 200 pc (refs 1,4), the proper motions of the other components correspond to a tangential velocity of 44 to 160 km s^-l with respect to the Mira. By combining these measurements with radial velocity determinations, we obtain a true three-dimensional velocity map of the radio jet, provided only that the observed proper motions indeed correspond to physical motions of emitting material. Our results rule out the possibility that the radio components in the jet were formed in a single explosive event, and suggest instead that they are 'bullets' ejected at ∼20-yr intervals into a narrow cone. Alternatively, if the components move along the jet and are accelerated during the whole of their passage through the inner 7 arcsec (1,400 AU) of the system, ejection at ∼40-yr intervals would lead to the disposition observed at present.