Spatial Distribution of AlO in a High-mass Protostar Candidate Orion Source I

High-temperature molecular gas containing metallic elements is potentially a good probe to trace the kinematics/dynamics of circumstellar disks, and its presence in circumstellar disks around young stellar objects (YSOs) may also give some insights into formation processes of high-temperature meteoritic components formed in the Sun's protoplanetary disk. The Orion Kleimann–Low (KL) region is the most famous and nearest massive star formation site, and has been extensively studied since the 1970s. The KL region harbors a candidate high-mass YSO, Source I, which has a hot circumstellar rotating gas disk emanating a magnetocentrifugal wind of SiO. In this study, we report spatially resolved distributions of aluminum monoxide (AlO) emission lines at 497 and 650 GHz in the rotating outflow of Orion Source I based on subarcsecond observations obtained by the Atacama Large Millimeter/Submillimeter Array for the first time in star-forming regions. These AlO emissions are detected only at the base of the outflow as the high excitation line of H2O in spite of their low excitation temperatures. The limited distribution of AlO to the launching point of the outflow indicates that AlO is not in the gas phase in the outer part of the outflow lobes away from the disk surface, which could be attributed to recondensation of AlO as dust due to its refractory nature.