A Triple Radio Continuum Source Associated with IRAS 16547–4247: A Collimated Stellar Wind Emanating from a Massive Protostar

Abstract

We report the discovery, made using the Australia Telescope Compact Array, of a triple radio source toward IRAS 16547-4247, a luminous infrared source with a bolometric luminosity of 6.2 × 104 L☉. The radio source shows an almost linear structure consisting of a compact central object and two outer lobes separated by about 20'', located symmetrically to the central source. The radio emission from the lobes has spectral indices of -0.61 and -0.33, characteristic of nonthermal emission. The emission from the central object has a spectral index of 0.49, consistent with free-free emission from a thermal jet. Also reported are 1.2 mm continuum and molecular line observations made with the Swedish ESO Submillimeter Telescope. The 1.2 mm observations show that the dust emission arises from a region of 33'' × 25'' (FWHM) with a total flux of 16.4 Jy, implying a mass of 1.3 × 103 M☉. The line observations indicate that IRAS 16547-4247 is associated with a molecular core with a FWHM deconvolved angular size of 27'' (diameter of 0.38 pc at the distance of 2.9 kpc), a molecular hydrogen density of 5.2 × 105 cm-3, and a mass of 9.0 × 102 M☉. We propose that this dense massive core hosts a high-mass star in an early stage of evolution in which it is undergoing the ejection of a collimated stellar wind. The radio emission from the lobes arises in shocks resulting from the interaction of this collimated wind with the surrounding medium. Our observations indicate that the jets found in the formation of low-mass stars are also produced in high-mass stars, with IRAS 16547-4247 being the most luminous young stellar object presently known to host a jet.