Accurate water maser positions from HOPS
  We report on high spatial resolution water maser observations, using the
Australia Telescope Compact Array, towards water maser sites previously
identified in the H2O southern Galactic Plane Survey (HOPS). Of the 540 masers
identified in the single-dish observations of Walsh et al. (2011), we detect
emission in all but 31 fields. We report on 2790 spectral features (maser
spots), with brightnesses ranging from 0.06 Jy to 576Jy and with velocities
ranging from -238.5 to +300.5km/s. These spectral features are grouped into 631
maser sites. We have compared the positions of these sites to the literature to
associate the sites with astrophysical objects. We identify 433 (69 per cent)
with star formation, 121 (19 per cent) with evolved stars and 77 (12 per cent)
as unknown. We find that maser sites associated with evolved stars tend to have
more maser spots and have smaller angular sizes than those associated with star
formation. We present evidence that maser sites associated with evolved stars
show an increased likelihood of having a velocity range between 15 and 35 km/s
compared to other maser sites. Of the 31 non-detections, we conclude they were
not detected due to intrinsic variability and confirm previous results showing
that such variable masers tend to be weaker and have simpler spectra with fewer
peaks.
