The Earliest Phases of Star formation (EPoS)

Temperature, density, and kinematic structure of the star-forming core CB 17^⋆

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
e-mail: schmalzl@strw.leidenuniv.nl
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁴ Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany

Received: 29 June 2013
Accepted: 25 May 2014

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.