2007A&A...470..269Z

Studies of high-mass protostellar objects reveal important information regarding the formation process of massive stars. We study the physical conditions in the dense core and molecular outflow associated with the high-mass protostellar candidate IRAS 18566+0408 at high angular resolution. We performed interferometric observations in the NH₃(J,K)=(1,1), (2,2) and (3,3) inversion transitions, the SiO J=2-1 and HCN J=1-0 lines, and the 43 and 87GHz continuum emission using the VLA and OVRO. The 87GHz continuum emission reveals two continuum peaks MM-1 and MM-2 along a molecular ridge. The dominant peak MM-1 coincides with a compact emission feature at 43GHz, and arises mostly from the dust emission. For dust emissivity index β of 1.3, the masses in the dust peaks amount to 70M_☉ for MM-1, and 27M_☉ for MM-2. Assuming internal heating, the central luminosities of MM-1 and MM-2 are 6x10⁴ and 8x10³L_☉, respectively. The SiO emission reveals a well collimated outflow emanating from MM-1. The jet-like outflow is also detected in NH₃at velocities similar to the SiO emission. The outflow, with a mass of 27M_☉, causes significant heating in the gas to temperatures of 70K, much higher than the temperature of ≲15K in the extended core. Compact (<3'') and narrow line (<1.5km/s) NH₃(3,3) emission features are found associated with the outflow. They likely arise from weak population inversion in NH₃similar to the maser emission. Toward MM-1, there is a compact NH₃structure with a linewidth that increases from 5.5km/s FWHM measured at 3'' resolution to 8.7km/s measured at 1'' resolution. This linewidth is much larger than the FWHM of <2km/s in the entire core, and does not appear to originate from the outflow. This large linewidth may arise from rotation/infall, or relative motions of unresolved protostellar cores.