VLBI aperture synthesis observations of the OH maser source W75 N

VLBI aperture synthesis observations of OH maser emission from the source W75 N, which is situated within the Cygnus X H II complex, are presented. A map of the maser emission and an accurate source position were obtained at 1665 MHz by a network of seven telescopes across the United States which provided a synthesized beam of approximately 0.015 arcsec diameter. The maser emission is found to be along an approximately north-south axis, with a velocity gradient from 13.2 km/sec in the south to 3.8 km/sec in the north, suggesting that the OH masers are contained in a rotating disk surrounding the ultracompact H II region. Two Zeeman pairs are identified in the maser emission, indicating magnetic field intensities of from approximately 3 to 5 milligauss. Observations of the continuum emission from W75 N made using the VLA suggest a complex structure for the ultracompact H II region, which is explained by a model of W75 N as a young binary stellar system.