Astron. Astrophys. 333, L63-L66 (1998)

Letter to the Editor

Infrared lasers in the circumstellar disk of MWC 349 ^*

C. Thum ¹, J. Martín-Pintado ², A. Quirrenbach ³ and H.E. Matthews <sup>4

1</sup> Institut de Radio Astronomie Millimétrique, 300 Rue de la piscine, F-38406 Saint Martin d'Hères, France
² Observatorio Astronómico Nacional, Campus Universitario, Guadalajara, Spain
³ Max-Planck-Institut für Extraterrestrische Physik, Garching bei München, Germany
⁴ Joint Astronomy Centre, Hilo, Hawaii, USA and National Research Council of Canada, Victoria, B.C., Canada

Received 2 December 1997 / Accepted 19 February 1998

Abstract

Observations of hydrogen recombination lines were made with the Infrared Space Observatory (ISO) towards the star MWC 349, where the -transitions at short millimeter and submillimeter wavelengths have been found to be masers. All -line s in the ISO wavelength range from 2.4 to 190µm (quantum numbers to 15) were detected. We find that amplification persists down to 19µm (), showing that these lines are infrared lasers. Our measurements permit for the first time a global view of the quantum number range of the recombination line laser/maser phenomenon, and suggest a peak amplification near in the unexplored region around m. The entire laser/maser phenomenon can be described quantitatively by case B recombination in a plasma with electron densities peaking at cm^-3, as expected in the corona of the circumstellar disk. In this model, the maser turns off at long wavelengths because the disk dimensions do not permit coherent gain paths longer than a.u. At short wavelengths, inversion ceases probably because the level populations are thermalized as a consequence of trapping of line photons for .

Key words: maser infrared: stars stars: individual: MWC 349

* Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA.

Send offprint requests to: C. Thum

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Contents

• 1. Introduction
• 2. Observations
• 3. Discussion
  • 3.1. Lasers
  • 3.2. A simple model
• 4. Conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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