Oscillating Filaments: I - Oscillation and Geometrical Fragmentation
  We study the stability of filaments in equilibrium between gravity and
internal as well as external pressure using the grid based AMR-code RAMSES. A
homogeneous, straight cylinder below a critical line mass is marginally stable.
However, if the cylinder is bent, e.g. with a slight sinusoidal perturbation,
an otherwise stable configuration starts to oscillate, is triggered into
fragmentation and collapses. This previously unstudied behavior allows a
filament to fragment at any given scale, as long as it has slight bends. We
call this process `geometrical fragmentation'. In our realization the spacing
between the cores matches the wavelength of the sinusoidal perturbation,
whereas up to now, filaments were thought to be only fragmenting on the
characteristical scale set by the mass-to-line ratio. Using first principles,
we derive the oscillation period as well as the collapse timescale
analytically. To enable a direct comparison with observations, we study the
line-of-sight velocity for different inclinations. We show that the overall
oscillation pattern can hide the infall signature of cores.
