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

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 HCOOCH 3 (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 HCOOCH 3 velocity gradient is not exactly perpendicular to the outflow axis but between an assumed disk plane and the outflow axis. We interpret these HCOOCH 3 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 HCOOCH 3 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.