2020ApJ...889..155W

We imaged the continuum and molecular line emission from Orion Source I (SrcI) with up to 30 mas (12 au) resolution at 43, 99, 223, and 340 GHz in an attempt to probe the structure and chemistry of the circumstellar disk and bipolar outflow associated with this high-mass protostar. The continuum spectral index ranges from ∼2 along the midplane of the disk to ∼3 along the edges, consistent with dust that is optically thick in the midplane but becomes optically thin at the periphery. Salt (NaCl) emission is visible where the dust is optically thin; it provides a unique tracer of the velocity field within the disk. All other molecules that we have mapped-H₂O, AlO, SiO, SiS, SO, and SO₂-appear to originate primarily in the bipolar outflow. The base of the outflow is corotating with the disk. SiS shows a filamentary structure that is most prominent along the edges of the outflow. The molecular distributions suggest that Si and Al released from dust grains in the disk react with oxygen derived from H₂O to form SiO and AlO, and with SO and SO₂ to form SiS.