STIMULATED RATIO RECOMBINATION LINE EMISSION AT 13 CENTIMETERS TOWARD MWC 349

High angular resolution (0.''065) observations of the H66alpha recombination line and continuum emission at 22.4 GHz toward the ionized wind in MWC 349 are presented. The continuum emission shows that the neutral material around the central star is distributed in a torus with a thickness of approximately 80 AU and an inner radius of approximately 100 AU. The H66alpha integrated line intensities are larger, by a factor of approximately 5, than the expected spontaneous emission. Thus, we suggest that stimulated emission makes a significant contribution to the observed line intensities. We present a radiative transfer model in which the asymmetric shape of the measured profiles and the spatial distribution of the H66alpha line are explained by radiative transfer models for a bipolar ionized wind expanding at constant velocity when non-LTE effects are taken into account. The non-LTE model products line intensities which are within a factor of approximately 1.4 of the observed intensities. The discrepancies between the non-LTE predictions and the observations are probably due to the presence of density and temperature inhomogeneities in the wind and/or uncertainties in the LTE departure coefficients used in our calculations. The origin of the centimeter recombination line emission in MWC 349 is briefly discussed. It is suggested that the intensity and the spatial distribution of recombination line emission can be used to show the presence of ionized bipolar outflows confined by neutral disks.