2018ApJ...860..119G

We report ALMA long-baseline observations of Orion Source I (SrcI), with a resolution 0.''03-0.''06 (12-24 au) at 1.3 and 3.2 mm. We detect both continuum and spectral line emission from SrcI's disk. We also detect a central weakly resolved source that we interpret as a hot spot in the inner disk, which may indicate the presence of a binary system. The high angular resolution and sensitivity of these observations allows us to measure the outer envelope of the rotation curve of the H₂O 5_5,0–6_4,3 line, which gives a mass M_I ≃ 15 ± 2 M_☉. We detected several other lines that more closely trace the disk, but were unable to identify their parent species. Using centroid-of-channel methods on these other lines, we infer a similar mass. These measurements solidify SrcI as a genuine high-mass protostar system and support the theory that SrcI and the Becklin-Neugebauer Object were ejected from the dynamical decay of a multiple-star system ∼500 years ago, an event that also launched the explosive molecular outflow in Orion.