Non-linear dense core formation in the dark cloud L1517
  We present a solution for the observed core fragmentation of filaments in the Taurus L1517 dark cloud which previously could not be explained (Hacar et. al 2011). Core fragmentation is a vital step for the formation of stars. Observations suggest a connection to the filamentary structure of the cloud gas but it remains unclear which process is responsible. We show that the gravitational instability process of an isothermal cylinder can account for the exhibited fragmentation under the assumption that the perturbation grows on the dominant wavelength. We use numerical simulations with the code RAMSES, estimate observed column densities and line-of-sight velocities and compare them to the observations. A critical factor for the observed fragmentation is that cores grow by redistributing mass within the filament and thus the density between the cores decreases over the fragmentation process. This often leads to wrong dominant wavelength estimates as it is strongly dependent on the initial central density. We argue that non-linear effects also play an important role on the evolution of the fragmentation. Once the density perturbation grows above the critical line-mass, non-linearity leads to an enhancement of the central core density in comparison to the analytical prediction. Choosing the correct initial conditions with perturbation strengths of around 20\%, leads to inclination corrected line-of-sight velocities and central core densities within the observational measurement error in a realistic evolution time. 
Stefan Heigl, Andreas Burkert, Alvaro Hacar
astro-ph.SR astro-ph.GA