2019ApJ...872...64K

We present high-resolution images of the submillimeter SiO line emissions of a massive young stellar object Orion Source I using the Atacama Large Millimeter/submillimeter Array at band 8. We detected the 464 GHz SiO v = 4 J = 11-10 line in Source I, which is the first detection of the SiO v = 4 line in star-forming regions, together with the 465 GHz ²⁹SiO v = 2 J = 11-10 and the 428 GHz SiO v = 2 J = 10-9 lines with a resolution of 50 au. The ²⁹SiO v = 2 J = 11-10 and SiO v = 4 J = 11-10 lines have compact structures with a diameter of <80 au. The spatial and velocity distributions suggest that the line emissions are associated with the base of the outflow and the surface of the edge-on disk. In contrast, SiO v = 2 J = 10-9 emission shows a bipolar structure in the direction of northeast-southwest low-velocity outflow with a ∼200 au scale. The emission line exhibits a velocity gradient along the direction of the disk elongation. With the assumption of the ring structure with Keplerian rotation, we estimated the lower limit of the central mass to be 7 M_☉ and the radius to be 12 au < r < 26 au.