VLBI aperture synthesis observations of the OH maser source W75 N

Abstract

We conducted very long baseline interferometric (VLBI) observations of the OH maser source in W75 N at 1665 MHz. The OH emission was mapped with aperture synthesis techniques using a seven station array of telescopes across the United States which provided a synthesized beam of approx.0.''015 diameter. The maser emission consists of nine components in an elongated region that has a major axis of 1.''5 (0.15 pc) and a position angle of 20/sup 0/. The maser components systematically increase in velocity from 3.8 to 13.2 km s/sup -1/ along this axis. The absolute position of the OH maser source was measured to an accuracy of 0.''2, confirming the association of the OH maser with the ultracompact H II region W75 N. Very large array observations of the continuum emission from W75 N at 4885 MHz indicate that the OH maser components are aligned with an extension of the ultracompact H II region. Our observations suggest that a binary protostellar system may excite the H II region, and that the OH maser reside in a rotating disk of remnant material out of which the binary formed.