Conical Winds and Axial Jets from the Disk-Magnetosphere Boundary

Abstract

We investigate the launching of outflows from the disk‐magnetosphere boundary of slowly and rapidly rotating magnetized stars using axisymmetric magnetohydrodynamic (MHD) simulations. We find long‐lasting outflows in both cases. (1) In the case of slowly rotating stars, a new type of outflow, a conical wind, is found and studied in simulations. The conical winds appear in cases where the magnetic flux of the star is bunched up by the disk into an X‐type configuration. The winds have the shape of a thin conical shell with a half‐opening angle θ∼30°–40°. About 10–30% of the disk matter flows from the inner disk into the conical winds. The conical winds may be responsible for episodic as well as long‐lasting outflows in different types of stars. There is also a low‐density, higher velocity component (a jet) in the region inside the conical wind. (2) In the case of rapidly rotating stars (the “propeller regime”), a two‐component outflow is observed. One component is similar to the conical winds. A significant fraction of the disk matter may be ejected into the winds. A second component is a high‐velocity, low‐density magnetically dominated axial jet where matter flows along the opened polar field lines of the star. The jet has a mass flux about 10% that of the conical wind, but its energy flux (dominantly magnetic) can be larger than the energy flux of the conical wind. The jet’s angular momentum flux (also dominantly magnetic) causes the star to spin‐down rapidly. Propeller‐driven outflows may be responsible for the jets in protostars and for their rapid spin‐down. The jet is collimated by the magnetic force while the conical winds are only weakly collimated in the simulation region.