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MWC 349A is one of the rare stars known to have hydrogen radio recombinationline (RRL) masers. The bright maser emission makes it possible to study thedynamics of the system at milli-arcsecond (mas) precision. We present AtacamaLarge Millimeter/submillimeter Array (ALMA) observations of the 1.4 mm and 0.8mm continuum emission of MWC 349A, as well as the H30$\alpha$ and H26$\alpha$RRLs. Using the most extended array configuration of C43-10 with a maximumbaseline of 16.2km, we spatially resolved the H30$\alpha$ line and 1.4mmcontinuum emission for the first time. In addition to the known H30$\alpha$ andH26$\alpha$ maser emission from a Keplerian disk at LSR velocities from -12 to28 km s$^{-1}$ and from an ionized wind for velocities between -12 to -40 kms$^{-1}$ and 28 to 60 km s$^{-1}$, we found evidence of a jet along the polaraxis at $V_{\mathrm{LSR}}$ from -85 to -40 km s$^{-1}$ and +60 to +100 kms$^{-1}$. These masers are found in a linear structure nearly aligned with thepolar axis of the disk. If these masers lie close to the polar axis, theirvelocities could be as high as 575 km s$^{-1}$, which cannot be explainedsolely by a single expanding wind as proposed in B\'aez Rubio et al (2013). Wesuggest that they originate from a high-velocity jet, likely launched by amagnetohydrodynamic wind. The jet appears to rotate in the same direction asthe rotation of the disk. A detailed radiative transfer modeling of theseemissions will further elucidate the origin of these masers in the wind.

Detection of a High-velocity Jet from MWC 349A Traced by Hydrogen Recombination Line Emission