The first detection of the 232GHz vibrationally excited H2O maser in Orion KL with ALMA

Abstract

We investigated the ALMA science verification data of Orion KL and found a spectral signature of the vibrationally excited H2O maser line at 232.68670GHz (ν2 = 1, 55, 0-64, 3). This line has been detected previously in circumstellar envelopes of late-type stars but not in young stellar objects such as Orion KL. Thus, this is the first detection of the 232GHz vibrationally excited H2O maser in star-forming regions. The distribution of the 232GHz maser is concentrated at the position of the radio Source I, which is remarkably different from other molecular lines. The spectrum shows a double-peak structure at the peak velocities of -2.1 and 13.3kms-1. It appears to be consistent with the 22GHz H2O masers and 43GHz SiO masers observed around Source I. Thus, the 232GHz H2O maser around Source I would be excited by the internal heating by an embedded protostar, being associated with either the root of the outflows/jets or the circumstellar disk around Source I, as traced by the 22GHz H2O masers or 43GHz SiO masers, respectively. © 2012 The American Astronomical Society. All rights reserved.