  Context. Low-mass star-forming cores differ from their surrounding molecular
cloud in turbulence, shape, and density structure. Aims. We aim to understand
how dense cores form out of the less dense cloud material by studying the
connection between these two regimes. Methods. We observed the L1517 dark cloud
in C18O(1-0), N2H+(1-0), and SO(JN=32-21) with the FCRAO 14m telescope, and in
the 1.2mm dust continuum with the IRAM 30m telescope. Results. Most of the gas
in the cloud lies in four filaments that have typical lengths of 0.5 pc. Five
starless cores are embedded in these filaments and have chemical compositions
indicative of different evolutionary stages. The filaments have radial profiles
of C18O(1-0) emission with a central flattened region and a power-law tail, and
can be fitted approximately as isothermal, pressure-supported cylinders. The
filaments, in addition, are extremely quiescent. They have subsonic internal
motions and are coherent in velocity over their whole length. The large-scale
motions in the filaments can be used to predict the velocity inside the cores,
indicating that core formation has not decoupled the dense gas kinematically
from its parental material. In two filaments, these large-scale motions consist
of oscillations in the velocity centroid, and a simple kinematic model suggests
that they may be related to core-forming flows. Conclusions. Core formation in
L1517 seems to have occurred in two steps. First, the subsonic,
velocity-coherent filaments have condensed out of the more turbulent ambient
cloud. Then, the cores fragmented quasi-statically and inherited the kinematics
of the filaments. Turbulence dissipation has therefore occurred mostly on
scales on the order of 0.5 pc or larger, and seems to have played a small role
in the formation of the individual cores.
