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

¹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA e-mail: qzhang@cfa.harvard.edu
² National Radio Astronomical Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475, USA
³ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany

Received: 12 January 2007
Accepted: 11 April 2007

Abstract

Context.Studies of high-mass protostellar objects reveal important information regarding the formation process of massive stars.

Aims. 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 and (3,3) inversion transitions, the SiO –1 and HCN –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  for MM-1, and 27  for MM-2. Assuming internal heating, the central luminosities of MM-1 and MM-2 are and  , respectively. The SiO emission reveals a well collimated outflow emanating from MM-1. The jet-like outflow is also detected in at velocities similar to the SiO emission. The outflow, with a mass of 27 , causes significant heating in the gas to temperatures of 70 K, much higher than the temperature of  K in the extended core. Compact () and narrow line (<1.5 km s^-1) (3,3) emission features are found associated with the outflow. They likely arise from weak population inversion in similar to the maser emission. Toward MM-1, there is a compact 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.