SIMBAD references

Protostellar jets are most probably disk winds or stellar winds collimated by rotating magnetospheres. The structure of these magnetospheres follows from solutions of the Grad-Schlueter-Shafranov (GSS) equation for the force-balance between axisymmetric magnetic surfaces. In this paper, two-dimensional force-free solutions of the relativistic GSS equation are numerically obtained for different field topologies of the underlying magnetosphere. Due to the high rotational periods observed for T Tauri stars, the light cylinder of rotating protostellar magnetospheres is within the observed jet radii. This requires a special relativistic treatment of the GSS equation, which is solved using the method of finite elements. In this approach, boundary conditions along the Alfven surface are automatically satisfied. The code enables the solution of the GSS equation in the entire domain between the stellar surface and the asymptotic jet region. The magnetosphere which carries the plasma flow is assumed to be generated by the central star. For stellar field strengths of the order of a kilo-Gauss, a gap between the stellar surface and the inner edge of the accretion disk opens up. Two different magnetic field topologies are considered depending on the behaviour of the magnetic fields near the inner accretion disk. In the case of accretion disks with high resistivity, a reversed field topology is built up along the accretion disk, and the current exchange between star and disk mainly flows in the inner magnetosphere. This is consistent with high mass-accretion along the dipolar stellar fields and small mass loss rates through the wind. In the case of accretion disks with low resistivity, a screw pinch topology results, since the accretion disk screens the magnetosphere of the star. Smooth field topologies can be calculated in this case which are collimated into asymptotic cylinders with radii of a few light cylinder radii. In general, such solutions are found to have kinks along the Alfven surface. For a proper adjustment of the underlying current distribution and the shape of the jet boundary, one can find magnetic field configurations without kinks at the Alfven surface. In this case, plasma flows smoothly through the Alfven surface. The distribution of the wind plasma is calculated from particular solutions of the wind equation. The paper mainly concentrates on protostellar jets since the stellar jet phenomenon is predominantly observed for young stellar objects. The results, however, are also applicable for other astronomical jets emerging from star-disk systems. In particular, the problem of magnetic fields with kinks at the light cylinder is well known in the context of pulsar magnetospheres. Our results provide a solution to this longstanding problem.