Astron. Astrophys. 361, 1169-1177 (2000)

Radiative transfer effects in hydrogen recombination masers

C. Hengel and W.H. Kegel

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

Received 7 April 2000 / Accepted 10 July 2000

Abstract

Using a simple on-the-spot approximation, we explore the parameter range in the plane for which maser action in atomic hydrogen is present and briefly discuss how the borderlines of this region of strong population inversion arise. In particular we address the influence of radiative transfer on the population structure. We find that in normal HII regions no strong maser activity occurs, while for ultra compact HII regions in a certain parameter range strong hydrogen masers should be found. Our fit to the available observational data for MWC 349 leads to a density estimate that is compatible with previous work (Thum & Greve 1997). Furthermore, we derive for the first time a reasonable representation of the variation of the flux ratio of and lines measured towards MWC 349.

Key words: masers radiative transfer stars: individual: MWC 349 stars: circumstellar matter ISM: H ii regions

Send offprint requests to: C. Hengel (hengel@astro.uni-frankfurt.de)

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Contents

• 1. Introduction
• 2. Theoretical concept and method of solution
  • 2.1. Basic equations
  • 2.2. Geometry
  • 2.3. Atomic data
  • 2.4. Method of computation
  • 2.5. Radiation emitted by the maser region
• 3. Population structure and line intensities
  • 3.1. The effect of radiative transfer in the spherically symmetric case
  • 3.2. Parameters for population inversion
  • 3.3. Ellipsoidal maser regions
• 4. Line intensities - comparison with observational data
• 5. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: October 10, 2000
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