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Hydrogen Recombination --Lines in MWC349

C. Thum , V. S. Strelnitski , J. Martín--Pintado , H. E. Matthews , H. A. Smith
Institut de Radio Astronomie Millimétrique, France
Laboratory for Astrophysics, National Air and Space Museum, Washington, D.C., USA
Centro Astronómico de Yebes, Apartado 148, E--19080 Guadalajara, Spain
Joint Astronomy Center, 660 N. A`ohoku Place, University Park, Hilo, Hawaii 96720, USA
Abstract: We have detected four --line s out of six observed in the frequency range from 100 to 400 GHz toward the radio star MWC349A. The detected --line s have similar parameters as the pedestal features of the short mm --line s and probably have the same origin in the ionized wind.

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 gain ().

next up previous contents
Next: The jet-driven molecular Up: Scientific Results Previous: A method to

Robert Lucas
Fri Mar 17 14:32:02 MET 1995