Geometry and velocity structure of HD 44179’s bipolar jet

In this paper we analyse a set of 33 optical spectra, which were acquired with the ARCES echelle spectrograph (R = 38,000) on the 3.5-m telescope at the Apache Point Observatory. We examine the H{\alpha} profile in each of these observations in order to determine the geometry and velocity structure of the previously discovered bipolar jet, which originates from the secondary star of HD 44179 located at the centre of the Red Rectangle nebula. Using a 3D geometric model we are able to determine the orbital coverage during which the jet occults the primary star. During the occultation, part of the H{\alpha} line profile appears in absorption. The velocity structure of the jet was determined by modelling the absorption line profile using the Sobolev approximation for each orbital phase during which we have observations. The results indicate the presence of a wide angle jet, likely responsible for observed biconical structure of the outer nebula. Furthermore, we were able to determine a likely velocity structure and rule out several others. We find that the jet is comprised of low-density, high-velocity, central region and a higher-density, lower-velocity, conical shell.