# A rotating fast bipolar wind and disk system around the B[e]-type star MWC 922

## TL;DR

This study uses high-resolution ALMA observations to reveal the detailed structure and kinematics of a rotating bipolar wind and disk system around the B[e]-type star MWC 922, providing new insights into its ionized environment.

## Contribution

First detailed imaging of the ionized region around MWC 922, showing a rotating disk, bipolar ejection, and wind with empirical evidence of rotation in high-velocity bipolar wind.

## Key findings

- Resolved a compact ionized region less than a few hundred au in size.
- Detected a nearly edge-on Keplerian disk around the star.
- Unveiled a fast bipolar ejection orthogonal to the disk.

## Abstract

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 unknown distance to the source is usually taken to be d=1.7-3 kpc. The unprecedented angular resolution (up to ~0.02arcsec) and exquisite sensitivity of these data unveil, for the first time, the structure and kinematics of the emerging, compact ionized region at its center. We imaged the line emission of H30a and H39a, previously detected with single-dish observations, as well as of H51epsilon, H55gamma, and H63delta, detected for the first time in this work. The line emission is seen over a full velocity range of ~180 km/s arising in a region of diameter <0.14arcsec (less than a few hundred au) in the maser line H30a, 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 ~10Msun (d=1.7 kpc) or ~18Msun (d=3 kpc), assuming Keplerian rotation. Our data also unveil a fast (~100 km/s) bipolar ejection (a jet?) orthogonal to the disk. In addition, a slow (<15km/s) wind may be lifting off 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 (~100 km/s). (abridged)