Testing the massive disk scenario for IRAS 18089-1732

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Abstract
Investigating in more detail the previously suggested massive disk scenario for the High-Mass Protostellar Object IRAS18089-1732, we observed the source in the 860mum band with the Submillimeter Array in various spectral lines and the submm continuum emission at (sub-)arcsecond spatial resolution. Fifty spectral lines from eighteen different species spanning upper level energy states between 17 and 747K were detected. One of the assumed best tracers for massive disks, CH3CN, is optically thick and does not allow a further disk investigation. However, the complex molecule HCOOCH3 appears optically thin and exhibits a velocity shift across the central core perpendicular to the emanating outflow. Assuming equilibrium between centrifugal and gravitational force, the estimated mass for this rotating structure is 16/(sin2(i))Msun (with i the unknown inclination angle), of the same order as the gas mass derived from the continuum emission. A temperature estimate based on the CH3CN(19--18) K-ladder results in ~350K, thus a hot core has already formed in this region. An analysis of the submm continuum emission reveals even at this high spatial resolution only one isolated massive dust core without any detectable companions down to mass limits between 0.2 and 3Msun (depending on the assumed temperature). Potential implications for the massive cluster formation are discussed.

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