Magnetised protostellar bipolar outflows: I. Self-similar model with Poynting flux

We study a self-similar circulation model for protostellar bipolar outflows. The model is axisymmetric and stationary, and now includes Poynting flux. Compared to an earlier version of the model, this addition produces faster and more collimated outflows. Moreover the luminosity needed for the radiative heating is smaller. The solutions are developed within the context of r-self-similarity, which is a separated type of solution wherein a power of r multiplies an unknown function of 6. For outflows surrounding a fixed point mass the velocity, density and magnetic field respectively scale with spherical radius r as υ ∝ r^-1/2, ρ ∝ r^2α-1/2 and Β ∝ r^α-3/4. The parameter α must be larger than -1/2 and smaller than or equal to 1/4. We obtain the θ-dependence of all flow quantities. Monte Carlo methods have been used to explore systematically the parameter space. An inflow/outflow pattern including collimation of high speed material and an infalling toroidal disc arises naturally. The disc shape depends on the imposed heating, but it is naturally Keplerian given the central point mass. Outflows can have large opening angles, that increase when the magnetic field weakens. Massive protostars produce faster but less collimated outflows than less massive protostars. The model is now at a stage where synthetic CO spectra reproduce very well the observational features. The results strengthen the idea that the Poynting flux and the radiative heating are ultimately the energy sources driving the outflow.