OH 12.8-0.9: A New Water-Fountain Source

Abstract

We present observational evidence that the OH/IR star OH 12.80.9 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 12.80.9. 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) masers located to the north 1 and the redshifted (32.0 to 35.5 km s) masers to the south. In addition, we find that the blue-and redshifted 1 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 12.80.9, the observed spatiokinematic structure of the H 2 O masers provides strong evidence that OH 12.80.9 is indeed a member of the water-fountain class.