2 00 3 A Class of Interstellar OH Masers Associated with Protostellar Outflows Alice

Using the Very Large Array, we have detected weak OH maser emission near the Turner–Welch protostellar source in the W3 OH region. Unlike typical interstellar OH masers, which are associated with ultra-compact HII regions, our measured positions and proper motions (from Very Long Baseline Interferometry) indicate that these OH masers are associated with a bipolar outflow traced by strong H2O masers. These OH masers may be part of a class of interstellar OH masers that are associated with very young stars which have yet to, or may never, create ultra-compact HII regions. This class of OH masers appears to form near the edges of very dense material (within which H2O masers form), where total densities drop precipitously and interstellar UV radiation is sufficient to dissociate the H2O molecules. Observations of this class of OH masers may be an important way to probe the distribution of this important molecule in interstellar shocks at arcsecond resolution or better. Subject headings: ISM: individual (W3)—ISM: jets and outflows—masers—radiation mechanisms: nonthermal—radio lines: ISM—stars: formation