Curved jet motion. I. Orbiting and precessing jets

Abstract

Astrophysical jets are often observed as bent or curved structures. We also know that the different jet sources may be binary in nature, which may lead to a regular, periodic motion of the jet nozzle, an orbital motion or precession. Here, we present the results of 2D (M)HD simulations in order to investigate how a precessing or orbiting jet nozzle affects the propagation of a high-speed jet. We have performed a parameter study of systems with different precession angles, orbital periods or separations, and different magnetic field strengths. We find that these kinds of nozzles lead to curved jet propagation which is determined by the main parameters that define the jet nozzle. We find C-shaped jets from orbiting nozzles and S-shaped jets from precessing nozzles. Over long time and long distances, the initially curved jet motion bores a broad channel into the ambient gas that is filled with high-speed jet material which lateral motion is damped, however. A strong (longitudinal) magnetic field can damp the jet curvature that is enforced by either precession of orbital motion of the jet sources. We have investigated the force balance across the jet and ambient medium and found that the lateral magnetic pressure and gas pressure gradients are almost balanced, but that a lack of gas pressure on the concave side of the curvature is leading to the lateral motion. Magnetic tension does not play a significant role. Our results are obtained in code units, but we provide scaling relations such that our results may be applied to young stars, micro-quasars, symbiotic stars or AGN.