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Appendix A: Description of toy radiative transfer models

Without attempting to directly model the velocity field of IRAS 17233, we used LIME radiative transfer models to determine what combination of outflow and rotational motions could cause a 45° degree offset between the large scale outflow and the small scale velocity gradients in the molecular gas.

To do this, we simplistically assumed temperature, density and velocity profiles of the form: where r, θ and φ represent the coordinate grid, β = 1, α = 1.5, f is the flattening parameter of the rotating structure (f = 5), r_d is the distance between VLA2a and VLA1 (2000 au), and r_{20 au} is the given radius outwards of 20 au, but fixed at 20 au for smaller radii to avoid a divide by zero. The resultant velocity grids from this modelling are shown in Fig. A.1. As shown here, a combination of purely rotational motion along the midplane, and outflow motion perpendicular to it creates a scenario where the observed combination of these two effects is a velocity gradient at 45° to both. The outer edges of the combined motions show where the density and temperature become low enough that OCS and H₂CO are no longer observable.

Fig. A.1 Toy radiative transfer models showing how rotational and outflow motions can combine to produce a velocity gradient that is halfway between the directions of the two dominant dynamical processes. From top to bottom, the panels show outflow motions only, rotational motions (perpendicular to the outflow) and the combined effects of the two when the outflow velocities are one third those of the rotational velocities at a radius of 1000 au.

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Appendix B: SiO and CS channel maps

Figures B.1 and B.2 show, respectively, the channel maps of the SiO and CS emission surrounding IRAS 17233 VLA2-1. The centre of each panel shows the same 48 GHz continuum

contours as previous figures for reference. Note that the sizes of each panel are consistent between the two figures, however the starting and ending velocities are slightly shifted to reflect the bulk of the emission for each of the two species.

	Fig. B.1 SiO channel map. The white contours indicate the 48 GHz continuum, consistent with previous figures, and the colour scale shows the SiO emission starting at 3σ.
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	Fig. B.2 CS channel map. The white contours indicate the 48 GHz continuum, consistent with previous figures, and the colour scale shows the CS emission starting at 3σ.
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© ESO, 2015