Interstellar Hydroxyl Masers in the Galaxy. I. The VLA Survey

Interstellar OH masers are bright signposts for recently formed massive stars, and the maser emission can be used to study the kinematic and physical conditions of dense molecular material surrounding these stars. We present interferometric maps of 91 interstellar OH maser sources in one or both of the ground-state, main-line, ²Π_3/2J=3/2 OH transitions near 18 cm wavelength. The maps comprising this large, uniformly processed, survey have a spectral resolution of 0.14 km s^-1 and an angular resolution of ~1.5". We measured the absolute positions of the masers to an accuracy of ~0.3" in the E-W direction and ~0.5" in the N-S direction, except for those sources with declinations below about -30°, and relative positions of isolated OH maser spots within each source and OH transition to an accuracy of ~0.01". This survey forms a nearly complete sample of interstellar OH masers that are stronger than 1 Jy in both right- and left-circular polarization in at least one of the ground-state OH transitions.