Protostellar collapse: regulation of the angular momentum and onset of
  an ionic precursor
  Through the magnetic braking and the launching of protostellar outflows,
magnetic fields play a major role in the regulation of angular momentum in star
formation, which directly impacts the formation and evolution of protoplanetary
disks and binary systems. The aim of this paper is to quantify those phenomena
in the presence of non-ideal magnetohydrodynamics effects, namely the Ohmic and
ambipola r diffusion. We perform three-dimensional simulations of protostellar
collapses varying the mass of the prestellar dense core, the thermal support
(the $\alpha$ ratio) and the dust grain size-distribu tion. The mass mostly
influences the magnetic braking in the pseudo-disk, while the thermal support
impacts the accretion rate and hence the properties of the disk. Removing the
grains smaller than 0. 1 $\mu$m in the Mathis, Rumpl, Nordsieck (MRN)
distribution enhances the ambipolar diffusion coefficient. Similarly to
previous studies, we find that this change in the distribution reduces the
magnet ic braking with an impact on the disk. The outflow is also significantly
weakened. In either case, the magnetic braking largely dominates the outflow as
a process to remove the angular momentum from t he disk. Finally, we report a
large ionic precursor to the outflow with velocities of several km s$^{-1}$,
which may be observable.
