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Description
We present interferometric observations with the Atacama Large Millimeter Array (ALMA) of the free-free continuum and recombination line emission at 1 and 3mm of the Red Square Nebula surrounding the B[e]-type star MWC922. The distance to the source, which is unknown, is usually taken to be d=1.7-3kpc. The unprecedented angular resolution (up to ~0.02") and exquisite sensitivity of these data reveal for the first time the structure and kinematics of the nascent compact ionized region at its center. We imaged the line emission of H30{alpha} and H39{alpha}, previously detected with single-dish observations, and of H51{epsilon}, H55{gamma}, and H63{delta}, detected for the first time in this work. The line emission is seen over a full velocity range of ~180km/s arising in a region of diameter <0.14" (less than a few hundred au) in the maser line H30{alpha}, which is the most intense transition reported here. We resolve the spatio-kinematic structure of a nearly edge-on disk rotating around a central mass of ~10M_{sun}_ (d=1.7kpc) or ~18M_{sun}_ (d=3kpc), assuming Keplerian rotation. Our data also reveal a fast (~100km/s) bipolar ejection (possibly a jet) orthogonal to the disk. In addition, a slow (<15km/s) wind may be emanating from the disk. Both, the slow and the fast winds are found to be rotating in a similar manner to the ionized layers of the disk. This represents the first empirical proof of rotation in a bipolar wind expanding at high velocity (~100km/s).
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