The Thermal Structure of Gas in Prestellar Cores: A Case Study of Barnard 68

Author(s)

Edwin A. Bergin, Sébastian Maret, Floris F. S. van der Tak, João Alves, Sean M. Carmody, Charles J. Lada

Abstract

We present a direct comparison of a chemical/physical model to multitransitional observations of C18O and 13CO toward the Barnard 68 prestellar core. These observations provide a sensitive test for models of low UV field photodissociation regions and offer the best constraint on the gas temperature of a prestellar core. We find that the gas temperature of this object is surprisingly low (~7-8 K), and significantly below the dust temperature, in the outer layers (AV<5 mag) that are traced by C18O and 13CO emission. As shown previously, the inner layers (AV>5 mag) exhibit significant freezeout of CO onto grain surfaces. Because the dust and gas are not fully coupled, depletion of key coolants in the densest layers raises the core (gas) temperature, but only by ~1 K. The gas temperature in layers not traced by C18O and 13CO emission can be probed by NH3 emission, with a previously estimated temperature of ~10-11 K. To reach these temperatures in the inner core requires an order of magnitude reduction in the gas to dust coupling rate. This potentially argues for a lack of small grains in the densest gas, presumably due to grain coagulation.

Organisation(s)

External organisation(s)

European Southern Observatory (Germany), Harvard-Smithsonian Center for Astrophysics, Max-Planck-Institut für Radioastronomie, University of Michigan

Journal

The Astrophysical Journal: an international review of astronomy and astronomical physics

Volume

645

Pages

369-380

ISSN

0004-637X

DOI

https://doi.org/10.1086/504310

Publication date

07-2006

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics

Keywords

Portal url

https://ucris.univie.ac.at/portal/en/publications/the-thermal-structure-of-gas-in-prestellar-cores-a-case-study-of-barnard-68(a895426d-919e-48f3-b9b1-0cb81ea8fca9).html