A non-LTE radiative transfer model to study ionized outflows and disks.
  The case of MWC349A
  Context. The best example of a massive star with an ionized outflow launched
from its photoevaporating disk is MWC349A. The large amount of reported
radio-continuum and radio-recombination line observations toward this galactic
UC-HII region offers a unique possibility to build a model of the ionized
envelope of this source.
  Aims. To understand the physical conditions and kinematics of the ionized
region of the circumstellar disk and also of the outflow of MWC349A.
  Methods. We compared the bulk of radio-continuum maps, radio-recombination
line profiles, and the H30alpha centroid map published to date with the
predictions of our non-LTE 3D radiative transfer model, MORELI (MOdel for
REcombination LInes), which we describe here in detail.
  Results. Our non-LTE 3D radiative transfer model provides new evidence that
the UC-HII region of MWC349A is composed of an ionized circumstellar disk
rotating in Keplerian fashion around a star of 38 solar mass, and an ionized
outflow expanding with a terminal velocity of 60 km/s and rotating in the same
sense as the disk. The model shows that while maser amplification is the
dominant process involved for Hn\alpha radio-recombination line (RRL) emission
with quantum numbers n<41, stimulated emission is relevant for the emission of
RRLs with n>41 up at least the H76alpha line.
  Conclusions. For the first time, we present a model of MWC349A which
satisfactorily explains the vast amount of reported observational data for a
very wide range of frequencies and angular resolutions.
