Detection of radio emission from the Becklin-Neugebauer object

Observations of the Becklin-Neugebauer object (BN) in the Orion-KL region made with the VLA (at 4.9, 15.0, and 22.8 GHz) and with the Hat Creek Millimeter Interferometer (HCMI) (at 87.6 GHz) during 1981 and 1982 are reported. No emission was detected with HCMI, implying a flux-density limit of 70 mJy. Emissions detected at 15 and 23 GHz correspond to a size less than 0.07 arcsec and a brightness temperature greater than 11,000 K; a VLA map of the region at 15 GHz is shown. The emission is considered optically thick (spectral index about 2) at 15-23 GHz, but thin above about 40 GHz. Two models which could explain the BN emissions are discussed: a compact H II region of uniform electron density (about 10 to the 7th/cu cm), or an ionized stellar wind (volume emission measure = about 10 to the 60th/cu cm) with a finite recombination radius. For either model the H mass is calculated as approximately 10 to the -6th solar mass, with a radius of about 3 x 10 to the 14th cm. A second radio source (3 mJy at 15 GHz) not coincident with an IR source was detected in the region, while no radio emission was detected from IRc2.