IRAS 18113-2503: the water fountain with the fastest jet?
  We present Expanded Very Large Array (EVLA) water maser observations at 22
GHz toward the source IRAS 18113-2503. Maser components span over a very high
velocity range of ~500 km/s, the second largest found in a Galactic maser, only
surpassed by the high-mass star forming region W49N. Maser components are
grouped into a blue and a redshifted cluster, separated by 0.12". Further
mid-IR and radio data suggest that IRAS 18113-2503 is a post-AGB star, thus a
new bona fide member of the rare class of "water fountains". It is the evolved
object with the largest total velocity spread in its water masers, and with the
highest velocity dispersion within its red- and blue-shifted lobes (~170 km/s).
The large total velocity range of emission probably indicates that IRAS
18113-2503 has the fastest jet among the known water fountain stars. On the
other hand, the remarkably high velocity dispersion within each lobe may be
interpreted in terms of shocks produced by an episode of mass ejection whose
velocity increased up to very high values or, alternatively, by projection
effects in a jet with a large opening angle and/or precessing motions.
