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

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4. Conclusion

The density structure of disk coronas which are photo-ionized by massive central stars has been investigated theoretically (Hollenbach et al. 1994). These models give the electron density at the base of the corona as a function of radial distance for several stellar masses. The model with a zero age main sequence star of 26 solar masses, such as derived for MWC 349 from the mm masers (Thum et al. 1994a), predict [FORMULA] [FORMULA] cm-3 at 40 a.u. where the H [FORMULA] masers are located. This remarkable agreement between theory and observation underlines that the laser/maser phenomenon observed here for the first time in its full extent occurs naturally in a configuration of a massive star surrounded by a dense disk. It is only required that the disk is seen roughly edge-on and that it is sufficiently large for the coherent gain paths along its surface.

These natural, single-pass, and high-gain lasers are powerful astrophysical tools for the investigation of the hot environment of massive young stars. The short-lived and small-scale, but energetic phenomena during the evolution of gaseous disks may be particularly promising targets. More objects like MWC 349 may be detectable when more sensitive spectrometers and more observing time becomes available near wavelengths of 300 µm where the recombination line laser/maser peaks.

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© European Southern Observatory (ESO) 1998

Online publication: April 20, 1998
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