A model for quasi-one-dimensional narrow jets

Abstract

We develop a quasi-one-dimensional model of a narrow jet by projecting the system of time-independent MHD equations onto the axis of the jet. This is done in analogy with the projection of equations onto the equatorial plane in thin accretion disk models. We use average values for the parameters of two coupled differential equations which relate the “line density” λ(z) (or the z-component of the velocity ν _z(z)) and the radius of the jet. We study the analytic structure of the equations and solve the system using parameters appropriate to some cases of astrophysical interest. We examine the importance of the coupling between rotation and magnetic fields as an acceleration mechanism in a jet and identify the physical consequences of different assumptions. The simplicity of our model, being one-dimensional, enables us to reduce it to one directly comparable with existing jet models.