Using chemistry to unveil the kinematics of starless cores: complex radial motions in Barnard 68

We present observations of (CO)-C-13, (CO)-O-18, HCO+, (HCO+)-C-13, DCO+, and N2H+ line emission toward the Barnard 68 starless core. The line profiles are interpreted by use of a chemical network coupled with a radiative transfer code, in order to reconstruct the radial velocity profile of the core. Our observations and modeling indicate the presence of complex radial motions, with inward motions in the outer layers of the core but outward motions in the inner layers of the core, suggesting radial oscillations. The presence of such oscillations would imply that the Barnard 68 starless core is relatively old, typically 1 order of magnitude older than the age inferred from its chemical evolution and statistical core lifetimes. Our study demonstrates that chemistry can be used as a tool to constrain the radial velocity profiles of starless cores.