A jet-like outflow toward the high-mass (proto) stellar object IRAS 18566+0408

Abstract

Context. Studies of high-mass protostellar objects reveal important information regarding the formation process of massive stars. Alms. 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. Methods. 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 V = 1-0 lines, and the 43 and 87 GHz continuum emission using the VLA and OVRO. Results. The 87 GHz 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 43 GHz, and arises mostly from the dust emission. For dust emissivity index β of 1.3, the masses in the dust peaks amount to 70 M ⊙ for MM-1, and 27 M⊙ for MM-2. Assuming internal heating, the central luminosities of MM-1 and MM-2 are 6 104 and 8 ×103 L⊙, respectively. The SiO emission reveals a well collimated outflow emanating from MM-1. The jet-like outflow is also detected in NH3 at velocities similar to the SiO emission. The outflow, with a mass of 27 M⊙, causes significant heating in the gas to temperatures of 70 K, much higher than the temperature of <15 K in the extended core. Compact (<3″) and narrow line (<1.5 km s -1) NH3 (3,3) emission features are found associated with the outflow. They likely arise from weak population inversion in NH3 similar to the maser emission. Toward MM-1, there is a compact NH3 structure with a linewidth that increases from 5.5 km s-1 FWHM measured at 3″ resolution to 8.7 km s-1 measured at 1″ resolution. This linewidth is much larger than the FWHM of <2 km s -1 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. © ESO 2007.