Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...287..325r&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 287, no. 1, p. 325-337
Astronomy and Astrophysics
Astrophysics
19
Accretion Disks, Astronomical Models, Magnetohydrodynamic Flow, Plasma Jets, Calculus Of Variations, Density (Mass/Volume), Kinetic Energy, Lagrangian Function, Mach Number, Temperature, Thrust, Velocity
Scientific paper
In order to achieve a fast MHD flow, a plasma ejected from the vicinity of a star or a compact object must fullfill restrictive conditions, because the flow is supposed to cross smoothly three critical surfaces, namely the slow magnetosonic surface, the Alfven surface and the fast magnetosonic surface. These surfaces are not known a priori. Moreover, there are other mathematical difficulties due to the change of the type of the partial differential equations, that pass from elliptical to hyperbolic and vice versa. We rounded these difficulties by using a variational method. We found a Lagrangian involving the two unknown functions of the problem, the local Mach number and the flux function. The accretion disk imposed boundary conditions having some self-similarity properties; which allows minimization of the Lagrange functional with a convergence sequence of appropriate trial functions. Our results confirm some previously published results (for instance, the cylindrical self-collimation), but also indicate some limitations about the acceleration region. Applications of the method concern both kinds of jets launched by an accretion disk and provide observational quantities such as velocity, density, temperature, size, flux of kinetic energy, thrust.
Pelletier Guy
Rosso Francoise
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