Submillimeter Array Outflow/Disk Studies in the Massive Star-forming Region IRAS 18089-1732

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Abstract
Submillimeter Array observations of the massive star-forming region IRAS 18089-1732 in the 1 mm and 850 μm band reveal outflow and disk signatures in different molecular lines. The SiO (5-4) data show a collimated outflow in the northern direction. In contrast, the HCOOCH3 (20-19) line, which traces high-density gas, is confined to the very center of the region and shows a velocity gradient across the core. The HCOOCH3 velocity gradient is not exactly perpendicular to the outflow axis but between an assumed disk plane and the outflow axis. We interpret these HCOOCH3 features as originating from a rotating disk that is influenced by the outflow and infall. On the basis of the (sub)millimeter continuum emission, the mass of the central core is estimated to be around 38 M☉. The dynamical mass derived from the HCOOCH3 data is 22 M☉, of about the same order as the core mass. Thus, the mass of the protostar/disk/envelope system is dominated by its disk and envelope. The two frequency continuum data of the core indicate a low dust opacity index β ~ 1.2 in the outer part, decreasing to β ~ 0.5 on shorter spatial scales.
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