How can outflows such as astrophysical winds and jets form and collimate? What differences exhibit these two types of plasma flows? This thesis attempts to answer those questions thanks to a simple model that deals with the time-independent and axisymmetric magnetohydrodynamic equations. The shape of the poloidal magnetic field lines is given up to the fast magnetosonic point. The transversal force balance is calculated along the Alfven surface, and the critically conditions are derived from the Bernoulli equation at the two other critical points. They are used to calculate the specific energy, the angular momentum and the mass loss rate, that are constant for each flux surface. This allows to deal with the asymptotic structure with respect to any conditions at the base of the outflow. It is found that rigid rotators can be divided into two main classes. On the one hand, we have the slow rotators associated to winds, that possess almost spherical critical surfaces and a diffused poloidal current, and on the other hand, fast rotators, that correspond to jets, whose critical surfaces are strongly distorted and whose current is important and concentrated around the axis of rotation. Regardless the class of rotator, the angular velocity is bounded from above for a given mass loss rate, and regardless an external confining pressure, the collimation of magnetic rotators is asymptotically cylindrical. Finally, the study of the linear stability using a normal mode analysis shows that axisymmetrical instabilities dominate internal mode ones. These instabilities could be at the origin of the knotty aspect of a large number of jets coming from young stellar objects.
|Original language||English (US)|
|Journal||Ph.D. Thesis, ULP Strasbourg, (1996)|
|State||Published - Dec 1 1996|
- ISM: JETS AND OUTFLOWS
- STARS: MASS-LOSS
- SOLAR WIND