## Detalles de publicación

PP 018081

## Self-Similar Approach for Rotating Magnetohydrodynamic Solar and Astrophysical Structures

(1) IAC, (2) ULL

Rotating magnetic structures are common in astrophysics, from vortex tubes

and tornados in the Sun all the way to jets in different astrophysical systems.

The physics of these objects often combine inertial, magnetic, gas pressure and

gravitational terms. Also, they often show approximate symmetries that help

simplify the otherwise rather intractable equations governing their morphology

and evolution. Here we propose a general formulation of the equations assuming

axisymmetry and a self-similar form for all variables: in spherical coordinates

$(r,\theta,\phi)$, the magnetic field and plasma velocity are taken to be of

the form: ${\bf B}={\bf f}(\theta)/r^n$ and

${\bf v}={\bf g}(\theta)/r^m$, with corresponding expressions for the scalar

variables like pressure and density. Solutions are obtained for potential,

force-free, and non-force-free magnetic configurations. Potential-field

solutions can be found for all values of~$n$. Non-potential force-free

solutions possess an azimuthal component $B_\phi$ and exist only for $n\ge2$;

the resulting structures are twisted and have closed field lines but are not

collimated around the system axis. In the non-force free case, including gas

pressure, the magnetic field lines acquire an additional curvature to

compensate for an outward pointing pressure gradient force. We have also

considered a pure rotation situation with no gravity, in the zero-$\beta$

limit: the solution has cylindrical geometry and twisted magnetic field lines.

The latter solutions can be helpful in producing a collimated magnetic field

structure; but they exist only when $n<0$ and $m<0$: for applications they must

be matched to an external system at a finite distance from the origin.

and tornados in the Sun all the way to jets in different astrophysical systems.

The physics of these objects often combine inertial, magnetic, gas pressure and

gravitational terms. Also, they often show approximate symmetries that help

simplify the otherwise rather intractable equations governing their morphology

and evolution. Here we propose a general formulation of the equations assuming

axisymmetry and a self-similar form for all variables: in spherical coordinates

$(r,\theta,\phi)$, the magnetic field and plasma velocity are taken to be of

the form: ${\bf B}={\bf f}(\theta)/r^n$ and

${\bf v}={\bf g}(\theta)/r^m$, with corresponding expressions for the scalar

variables like pressure and density. Solutions are obtained for potential,

force-free, and non-force-free magnetic configurations. Potential-field

solutions can be found for all values of~$n$. Non-potential force-free

solutions possess an azimuthal component $B_\phi$ and exist only for $n\ge2$;

the resulting structures are twisted and have closed field lines but are not

collimated around the system axis. In the non-force free case, including gas

pressure, the magnetic field lines acquire an additional curvature to

compensate for an outward pointing pressure gradient force. We have also

considered a pure rotation situation with no gravity, in the zero-$\beta$

limit: the solution has cylindrical geometry and twisted magnetic field lines.

The latter solutions can be helpful in producing a collimated magnetic field

structure; but they exist only when $n<0$ and $m<0$: for applications they must

be matched to an external system at a finite distance from the origin.