Magnetohydrodynamic jets from different magnetic field configurations

TL;DR

This study uses axisymmetric MHD simulations to explore how different magnetic field configurations influence jet formation, collimation, and stability, revealing key relations and potential flare-induced jet knots.

Contribution

It introduces a detailed analysis of how disk magnetic flux profiles and stellar magnetospheres affect jet collimation and stability in MHD simulations.

Findings

Collimation degree decreases with steeper magnetic field profiles.

Flat profiles produce highly collimated but unsteady outflows.

Strong flares can cause sudden changes in jet mass flux, possibly triggering knots.

Abstract

Using axisymmetric MHD simulations we investigate how the overall jet formation is affected by a variation in the disk magnetic flux profile and/or the existence of a central stellar magnetosphere. Our simulations evolve from an initial, hydrostatic equilibrium state in a force-free magnetic field configuration. We find a unique relation between the collimation degree and the disk wind magnetization power law exponent. The collimation degree decreases for steeper disk magnetic field profiles. Highly collimated outflows resulting from a flat profile tend to be unsteady. We further consider a magnetic field superposed of a stellar dipole and a disk field in parallel or anti-parallel alignment. Both stellar and disk wind may evolve in a pair of outflows, however, a reasonably strong disk wind component is essential for jet collimation. Strong flares may lead to a sudden change in mass flux by a factor two. We hypothesize that such flares may eventually trigger jet knots.