Fuse observations reveal the nature of the stellar jets in R aqr

Abstract

R Aquarii is a symbiotic system consisting of a Mira variable and a white dwarf companion. Its jet-like structures have been observed in the X-rays through the radio and extend up to 2500 AU from the central object. We report Far Ultraviolet Spectroscopic Explorer observations of OVI emission from these stellar jets that reveal signature line profiles of bow shocks. We have calculated bow shock models for a fully radiative shock, fully non-radiative shock, and a new hybrid set of models. We found that fully non-radiative shocks do not produce good fits to the data. While a fully radiative bow shock model cannot be excluded, the high densities required led us to develop hybrid bow shock models in which the shock is non-radiative near the apex of the bow shock, but becomes radiative at some distance from the apex. The model that best fits the data is the hybrid bow shock with a shock speed of approximately 235-285 km s-1 and an inclination angle of +10°and +35°with the plane of the sky for the northeast and the southwest jets, respectively. A turbulent velocity of about 60 km s-1 was required to obtain good fits. Surprisingly, both of the opposing jets have similar model parameters in spite of their very different OVI flux and distance from the central object. This analysis confirms the ejecta bow shock scenario as opposed to the cloudlet bow shock, constraining the mechanism of jet production to characteristics of the central object. The striking similarities in the physical parameters of the jets indicate a common origin and support the precessing accretion disk scenario for the white dwarf in the R Aqr system. For both jets we find pre-shock densities in the range of 103-104 cm-3 at positions of the brightest X-ray emission from the jets, which are also the positions of the apparent outer terminal points of the jets, providing strong support for the theory that the emission and shock structures we are seeing are produced when the jet material interacts with an external nebular wall. © 2009. The American Astronomical Society.