SENSITIVE VLA OBSERVATIONS OF OH-127.8-0.0 AND OH-26.5+0.6

VLA maps with the highest signal-to-noise ratio and dynamic range thus far observed for OH/IR stars are presented throughout the velocity range of the outer envelopes for the bright 1612 MHz sources OH 127.8-0.0 and OH 26.5+0.6. The maps are compared to VLBI and MERLIN data, and the shell parameters are determined to the highest accuracy obtainable with the assumptions of the standard expanding shell model. The linear radius of the maser shell of OH 127.8-0.0 is constant to within ±10% (rms) as a function of direction from the star, but that of OH 26.5+0.6 differs by as much as 50% on opposite sides of the shell, possibly because of excess ultraviolet radiation contributed by an O8 star in its vicinity. We consider the extent to which rotational components, radial acceleration, or random velocity fluctuations may be present in the envelopes. OH 127.8-0.0 appears to be a supergiant star, but its OH profile and light curve are unlike those of known supergiants.