Astron. Astrophys. 359, 405-412 (2000)

Non-LTE line formation in clumpy and turbulent molecular clouds

M. Hegmann and W.H. Kegel

Institut für Theoretische Physik der Johann Wolfgang Goethe Universität Frankfurt, Robert-Mayer-Strasse 8-10, 60054 Frankfurt am Main, Germany

Received 2 February 2000 / Accepted 4 May 2000

Abstract

Extending previous work (Albrecht & Kegel 1987, Kegel et al. 1993, Piehler & Kegel 1994), we investigated the formation of interstellar molecular lines in a medium with stochastic density and velocity fluctuations. We solved the full NLTE-problem, i.e. the generalized radiative transfer equation simultaneously with the rate equations, for a 6-level CO molecule and a plane-parallel slab geometry. Our results indicate that accounting for a finite correlation length of both, the density and velocity field, strongly affects the line profile and the line width as well as the intensity ratios of different rotational transitions.

Key words: line: formation radiative transfer ISM: clouds ISM: molecules radio lines: ISM

Send offprint requests to: M. Hegmann (Hegmann@astro.uni-frankfurt.de)

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Contents

• 1. Introduction
• 2. Basic equations
  • 2.1. Stochastic description of the velocity and density distribution
  • 2.2. About the structure of the density field
  • 2.3. Generalized transfer and rate equations
• 3. Results
  • 3.1. Microturbulence
  • 3.2. Turbulent velocity field with finite correlation length
• 4. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 30, 2000
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