2014A&A...569A...7S

The initial conditions for the gravitational collapse of molecular cloud cores and the subsequent birth of stars are still not well constrained. The characteristic cold temperatures (∼10K) in such regions require observations at sub-millimetre and longer wavelengths. The Herschel Space Observatory and complementary ground-based observations presented in this paper have the unprecedented potential to reveal the structure and kinematics of a prototypical core region at the onset of stellar birth. This paper aims to determine the density, temperature, and velocity structure of the star-forming Bok globule CB17. This isolated region is known to host (at least) two sources at different evolutionary stages: a dense core, SMM1, and a Class I protostar, IRS. We modeled the cold dust emission maps from 100µm to 1.2mm with both a modified blackbody technique to determine the optical depth-weighted line-of-sight temperature and column density and a ray-tracing technique to determine the core temperature and volume density structure. Furthermore, we analysed the kinematics of CB17 using the high-density gas tracer N₂H⁺. From the ray-tracing analysis, we find a temperature in the centre of SMM1 of T₀=10.6K, a flat density profile with radius 9.5x10³au, and a central volume density of n_H,0=2.3x10⁵cm^–3. The velocity structure of the N₂H⁺ observations reveal global rotation with a velocity gradient of 4.3km/s/pc. Superposed on this rotation signature we find a more complex velocity field, which may be indicative of differential motions within the dense core. SMM is a core in an early evolutionary stage at the verge of being bound, but the question of whether it is a starless or a protostellar core remains unanswered.