The Earliest Phases of Star formation (EPoS). Temperature, density, and kinematic structure of the star-forming core CB 17

Abstract

Context. 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 (~10 K) 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.
Aims: This paper aims to determine the density, temperature, and velocity structure of the star-forming Bok globule CB 17. 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.
Methods: We modeled the cold dust emission maps from 100 μm to 1.2 mm 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⁺.
Results: From the ray-tracing analysis, we find a temperature in the centre of SMM1 of T₀ = 10.6 K, a flat density profile with radius 9.5 × 10³ au, and a central volume density of n_H,0 = 2.3 × 10⁵ cm^-3. The velocity structure of the N₂H⁺ observations reveal global rotation with a velocity gradient of 4.3 km s^-1 pc^-1. Superposed on this rotation signature we find a more complex velocity field, which may be indicative of differential motions within the dense core.
Conclusions: 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.

The Herschel data (Fig. 2) including N- and T-maps in Fig. 3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/569/A7