年青星体附近双极喷流及其块状结构的物理机制

On the Formation and the Knotty Structure of Bipolar Jets near Young Stellar Objects

本文用磁拉瓦尔管机制解释了双极喷流的形成。这样,喷流内部的热压力被外部纵向磁场的磁压所平衡。本文研究了这一平衡态基础上的Kelvin-Helmholtz不稳定性,得出了共振模式的分析解。这一族解可解释喷流块状结构的许多观测特点,如块状结构的间距。高本动速度及喷流膨胀段的光学不可见性等等。

It is shown that a field strength of-1.6 milligauss at the inner part of the to-roid around a young stellar object is enough to hold the lateral expansion of the stellar wind of Mw - 4 × 10-9M yr-1 and Fw - 300kms-1 at a distance smaller than 3 × 1015cm, as required by observations. Thus,the wind material has to turn its way to the vertical directions through a 'magnetic de Laval nozzle'. The thermal pressure of the jet is balanced by the external magnetic pressure, of the longitudinal field.The Kelvin-Helmholtz instability of such an equilibrium state is investigated. A simple analytical method is developed for the resonant pinch modes. The properly scaled growth rates, wave numbers and phase speeds of the first ten resonant pinch modes are plotted against a single parameter, the ratio between the external Alfven speed and the internal sound speed. Many observational features, such as the knot space, the high proper motions, and the optical invisibility of the expansion part of the jet, can all be explained by this model.This is only a brief report. Detailed derivations and calculations will be published elsewhere.