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# A dynamical model for the dusty ring in the Coalsack

 Hennebelle, P., Whitworth, Anthony Peter and Goodwin, S. P. 2006. A dynamical model for the dusty ring in the Coalsack. Astronomy and Astrophysics 451 (1) , pp. 141-146. 10.1051/0004-6361:20054634

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## Abstract

Lada et al. recently presented a detailed near-infrared extinction map of Globule G2 in the Coalsack molecular cloud complex, showing that this starless core has a well-defined central extinction minimum. We propose a model for G2 in which a rapid increase in external pressure is driving an approximately symmetric compression wave into the core. The rapid increase in external pressure could arise because the core has recently been assimilated by the Coalsack cloud complex, or because the Coalsack has recently been created by two large-scale converging flows. The resulting compression wave has not yet converged on the centre of the core, so there is a central rarefaction. The compression wave has increased the density in the swept-up gas by about a factor of ten, and accelerated it inwards to speeds of order $0.4\,{\rm km}\,{\rm s}^{-1}$. It is shown that even a low initial level of turbulence completely destroys the coherence of the ring, as seen in projection. In the scenario of strong external compression that we are proposing this implies that the initial turbulent energy in the globule was low, $E_{{\rm TURB}}/\vert E_{{\rm GRAV}}\vert \leq 2\%$. Protostar formation should occur in about 40 000 years.

Item Type: Article Publication Published Physics and Astronomy Q Science > QB Astronomy ISM: clouds; stars: formation; hydrodynamics; instabilities; shock waves Pdf uploaded in accordance with publisher's policy at http://www.sherpa.ac.uk/romeo/issn/0004-6361/ (accessed 17/04/2014) EDP Sciences 0004-6361 30 March 2016 04 Jun 2017 04:55 http://orca-mwe.cf.ac.uk/id/eprint/46501