Interferometric confirmation of "water fountain" candidates
  Water fountain stars (WFs) are evolved objects with water masers tracing
high-velocity jets (up to several hundreds of km s$^{-1}$). They could
represent one of the first manifestations of collimated mass-loss in evolved
objects and thus, be a key to understanding the shaping mechanisms of planetary
nebulae. Only 13 objects had been confirmed so far as WFs with interferometer
observations. We present new observations with the Australia Telescope Compact
Array and archival observations with the Very Large Array of four objects that
are considered to be WF candidates, mainly based on single-dish observations.
We confirm IRAS 17291-2147 and IRAS 18596+0315 (OH 37.1-0.8) as bona fide
members of the WF class, with high-velocity water maser emission consistent
with tracing bipolar jets. We argue that IRAS 15544-5332 has been wrongly
considered as a WF in previous works, since we see no evidence in our data nor
in the literature that this object harbours high-velocity water maser emission.
In the case of IRAS 19067+0811, we did not detect any water maser emission, so
its confirmation as a WF is still pending. With the result of this work, there
are 15 objects that can be considered confirmed WFs. We speculate that there is
no significant physical difference between WFs and obscured post-AGB stars in
general. The absence of high-velocity water maser emission in some obscured
post-AGB stars could be attributed to a variability or orientation effect.
