Nonradial and nonpolytropic astrophysical outflows

Abstract

Abstract. By means of a nonlinear separation of the variables in the governing full set of the magnetohydrodynamic (MHD) equations for axisymmetric plasmas we analyse an exact model for magnetized and rotating outflows that are hotter and overpressured at their axis. These outflows start subsonically and subAlfvénically from the central gravitating source and its surrounding accretion disk. Subsequently, they accelerate thermally and magnetocentrifugally and thus cross the appropriate MHD critical points, reaching high values of the Alfvén Mach number. Three types of solutions are found: (a) collimated jettype outflows from efficient magnetic rotators with the flow confined by the magnetic hoop stress; (b) radially expanding windtype outflows analogous to the solar wind, from inefficient magnetic rotators or strongly overpressured sources; (c) terminated solutions with increasing amplitude of oscillations in the width of the beam. In contrast to previously studied underpressured outflows, the transition from collimated jets to uncollimated winds is not continuous in the appropriate parametric space with a gap where no stationary solution is found. Superfast at infinity solutions are filtered by three critical surfaces corresponding to the three known limiting characteristics or separatrices of MHD wind theory. Collimated and terminated solutions cross the slow, Alfvén and fast magneto-acoustic critical points. Radially expanding solutions cross the slow and Alfvén critical points while the last boundary condition is imposed by requiring that the pressure vanishes at infinity.

Two-component magnetohydrodynamical outflows around young stellar objects

“…13). Thus, all these facts suggest that the very inner part of the outflow, the so-called spine jet, behave as a meridionally-self-similar jet as in Sauty et al (2002Sauty et al ( , 2004. We observe that this is a kind of "hollow" stellar jet "thermally" driven and both magnetically and thermally confined inside the "hollow" disc jet.…”

“…This explains the difference from a model of Matt & Balick (2004) where the stellar wind is the only outflow and which is prone to a dipolar expansion. In our simulation, we self-consistently describe the acceleration of the inner jet in addition to its collimation, something that can be compared with analytical modeling (Sauty et al 2002(Sauty et al , 2004. Part of both the thermal energy deposited at the surface of the corona near the polar axis and the energy deposited by the turbulence in the stellar wind is transformed into kinetic energy (Fig.…”

Nonradial and nonpolytropic astrophysical outflows

“…This was far from obvious because the heating function is not polytropic as usually in most analytical solutions. In a series of papers - Sauty et al (1999, hereafter STT99), STT02, and Sauty et al (2004, hereafter STT04) -we have systematically explored the full parameter space of this problem. In ST94 we have shown that the double disk and star component was promising.…”

Three‐dimensional Magnetohydrodynamic Simulations of Jets from Accretion Disks

“…It was also found that the dependence of the mass accretion rate (Ṁ a ¼ dM a /dt) on the initial field strength is given byṀ a / B 1:4 0 / E 0:7 mg . In addition to these studies, the acceleration and collimation of the jet have been studied in the steady (e.g., Sauty et al 2004;Bogovalov & Tsinganos 2005) and nonsteady framework (e.g., Matsumoto et al 1996;Kato et al 2002;Krasnopolsky et al 2003; see also for a review). In recent years, interesting simulations taking other physical processes into consideration, e.g., the magnetic diffusion (Kuwabara et al 2000;Fendt & Č emeljić 2002;Casse & Keppens 2002, the dynamo process in the accretion disk (von Rekowski et al 2003), and the radiation force (Proga 2003), have been performed.…”