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Session 47 - Circumstellar Disks & Shells.
Display session, Thursday, January 08
Exhibit Hall,
MWC\,349 is a peculiar emission line star; among its outstanding features are strong hydrogen recombination line masers associated with the circumstellar disk. We have observed MWC\,349 with the SWS and LWS grating spectrometers on the ISO satellite. The spectrum covers the full wavelength range from 2.35\,\mum to 190\,\mum. Numerous hydrogen and helium recombination lines have been detected, along with about 30 fine structure lines, and the continuum emission from hot circumstellar dust. The fine structure lines cover ionization potentials up to about 50\,eV. For several elements, lines from different ionization stages are observed. This enables us to determine the effective temperature of the star. The uncertainty of the derived temperature is dominated by uncertainties in the stellar models used. Among the \sim 100 detected hydrogen recombination lines are all 12 \alpha-transitions within the wavelength range accessible to ISO, from Br\alpha at 4.05\,\mum to H\,15\alpha at 169.4\,\mum. The \alpha-lines with n \leq 6 are optically thick; the lines with higher n are amplified, and thus constitute infrared lasers. By combining the ISO results with millimeter and sub-millimeter data, we can produce the first global view on the recombination line laser / maser phenomenon in this star. We infer that the maximum line-integrated amplification -- by a factor of \sim 30 -- occurs in the region near n = 19 at \sim 300\,\mum.
