Chains of dense cores in the Taurus L1495/B213 complex
  (Abridged) We study the kinematics of the dense gas in the Taurus L1495/B213
filamentary region to investigate the mechanism of core formation. We use
observations of N2H+(1-0) and C18O(2-1) carried out with the IRAM 30m
telescope. We find that the dense cores in L1495/B213 are significantly
clustered in linear chain-like groups about 0.5pc long. The internal motions in
these chains are mostly subsonic and the velocity is continuous, indicating
that turbulence dissipation in the cloud has occurred at the scale of the
chains and not at the smaller scale of the individual cores. The chains also
present an approximately constant abundance of N2H+ and radial intensity
profiles that can be modeled with a density law that follows a softened power
law. A simple analysis of the spacing between the cores using an isothermal
cylinder model indicates that the cores have likely formed by gravitational
fragmentation of velocity-coherent filaments. Combining our analysis of the
cores with our previous study of the large-scale C18O emission from the cloud,
we propose a two-step scenario of core formation in L1495/B213. In this
scenario, named "fray and fragment," L1495/B213 originated from the supersonic
collision of two flows. The collision produced a network of intertwined
subsonic filaments or fibers ("fray" step). Some of these fibers accumulated
enough mass to become gravitationally unstable and fragment into chains of
closely-spaced cores. This scenario may also apply to other regions of star
formation.
