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

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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 4

1 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 [FORMULA] -transitions at short millimeter and submillimeter wavelengths have been found to be masers. All [FORMULA] -line s in the ISO wavelength range from 2.4 to 190µm (quantum numbers [FORMULA] to 15) were detected. We find that amplification persists down to 19µm ([FORMULA]), 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 [FORMULA] in the unexplored region around [FORMULA] m. The entire laser/maser phenomenon can be described quantitatively by case B recombination in a plasma with electron densities peaking at [FORMULA] 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 [FORMULA] a.u. At short wavelengths, inversion ceases probably because the level populations are thermalized as a consequence of trapping of line photons for [FORMULA].

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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© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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