We find that the flux ratios of -- and --line pedestals of nearly the same frequency are much smaller than expected from an optically thin plasma in LTE in all cases. We show with the help of simplified NLTE models of the recombination line emission that low --ratios are due to enhancement of the --line s by stimulated emission. This is a natural consequence of the high free--free continuum opacity in the ionized wind of MWC349A. The models also predict that the --ratio is a sensitive probe of the electron density. For the line emitting region the density thus derived is compatible with previous estimates, cm , based on a model of the wind's continuum emission.
The four newly detected --line s provide, together with the high frequency --line pedestals, the most reliable value of the center velocity of the ionized outflow, kms . This value agrees well with the centroid velocity of the disk, kms , as derived from the velocities of the blue and red maser spikes, and thus represents the best estimate of the stellar velocity.
H, at 366.6 GHz the highest frequency --line
observed to date, displays on top of the pedestal two
weak narrow emission features whose velocities and widths
are in qualitative agreement with those of the --line maser spikes. We
tentatively interpret these H spikes as a weak disk maser whose estimated
optical depth, , confirms earlier estimates of the --line maser