OH 12.8–0.9: A New Water-Fountain Source

We present observational evidence that the OH/IR star OH 12.8-0.9 is the fourth in a class of objects previously dubbed "water-fountain" sources. Using the Very Long Baseline Array, we produced the first images of the H2O maser emission associated with OH 12.8-0.9. We find that the masers are located in two compact regions with an angular separation of ~109 mas on the sky. The axis of separation between the two maser regions is at a position angle of 1.°5 east of north, with the blueshifted (-80.5 to -85.5 km s-1) masers located to the north and the redshifted (-32.0 to -35.5 km s-1) masers to the south. In addition, we find that the blue- and redshifted masers are distributed along arclike structures ~10-12 mas across, oriented roughly perpendicular to the separation axis. The morphology exhibited by the H2O masers is suggestive of an axisymmetric wind with the masers tracing bow shocks formed as the wind impacts the ambient medium. This bipolar jet-like structure is typical of the three other confirmed water-fountain sources. When combined with the previously observed spectral characteristics of OH 12.8-0.9, the observed spatiokinematic structure of the H2O masers provides strong evidence that OH 12.8-0.9 is indeed a member of the water-fountain class.