  The UC-HII region of MWC 349A is the prototype of an ionized wind driven by a
massive star surrounded by a disk. Recent high angular resolution observations
of the millimeter recombination lines have shown that the disk rotates with a
Keplerian law in its outer parts. However, the kinematics of innermost regions
in the UC-HII region of MWC 349A is still unknown, in particular the radius
where the wind is launched from the disk. We performed hydrogen recombination
line observations with the Heterodyne Instrument for the Far Infrared (HIFI)
onboard the Herschel Space Observatory to study the kinematics of its innermost
regions by studying their spectral features. In addition to the two laser
peaks, we report the first detection of two new components that are blueshifted
with respect to the laser peaks for all the recombination lines with principal
quantum number n<22. These new spectral features originate from the region
where the wind is ejected from the disk. We used our 3D non-LTE radiative
transfer model for recombination lines (MORELI) to show that these features are
consistent with the wind being ejected at a radius of about 24 AU from the
star, which supports magnetohydrodynamic wind models.
