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 H 2 O 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 H 2 O 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 H 2 O masers provides strong evidence that OH 12.8-0.9 is indeed a member of the water-fountain class.