The Parker instability in axisymmetric filaments: Final equilibria with
  longitudinal magnetic field
  We study the final equilibrium states of the Parker instability arising from
an initially unstable cylindrical equilibrium configuration of gas in the
presence of a radial gravitational field and a longitudinal magnetic field. The
aim of this work is to compare the properties of the nonlinear final equilibria
with those found in a system with Cartesian geometry. Maps of the density and
magnetic field lines, when the strength of the gravitational field is constant,
are given in both geometries. In the axisymmetric model, the magnetic field
tends to expand in radius, forming magnetic arcades, while knots of gas are
formed because the plasma drains radially and strangulates the magnetic field
lines, leading to the formation of magnetic bottlenecks. We find that the
magnetic buoyancy and the drainage of gas along field lines are less efficient
under axial symmetry than in a Cartesian atmosphere. As a consequence, the
column density enhancement arising in gas condensations in the
axially-symmetric model is smaller than in Cartesian geometry. The
magnetic-to-gas pressure ratio in the final state takes more extreme values in
the Cartesian model. Models with non-uniform radial gravity are also discussed.
